后端开发技术文章列表

详解http协议之使用抓包工具分析三次握手流程

后端
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<h1 style="box-sizing: border-box; margin: 0.3em 0px 1.25em; font-weight: 300; line-height: 1.2; font-size: 2.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.75em; border-bottom: 1px solid rgb(238, 238, 238);">抓包工具，查看TCP/IP的三次握手</h1><blockquote style="box-sizing: border-box; margin: 0px 0px 16px; border-left: 4px solid rgb(238, 238, 238); font-size: 14px; padding: 0px 15px 0px 20px; color: rgb(102, 102, 102); font-style: italic;"><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">经典的问题，你了解TCP/IP的三次握手吗？</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 0px;">四次挥手</p></blockquote><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">具体数据包的报文格式，暂时不用过多去琢磨；</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">什么时候需要琢磨数据包的序列号，只有当你在生产环境下，遇见的及其棘手的问题，比如一些数据不同步，交易数据丢失等极端情况，需要去抓取数据包，逐个分析，数据包的完整性，序列号。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">目前只需要大致了解数据包的类型，以及作用即可。</p><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>三次握手示意图</h3><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><img src="https://www.maxiaoke.com/uploads/images/20231227/9bd577cbd8517ce69239a961720090fc.png" alt=""/></p><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>模拟三次握手</h3><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">通过SSH登录过程，建立连接，从中抓取三次握手过程：</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">1. 抓取ssh登录的数据包，查看 tcp/ip协议基础之上的 SSH应用层协议登录web-7机器windows(192.168.xx.xx)  ↓vmnet8(nat虚拟网卡，10.0.0.1)    ↓web-7(nat 10.0.0.7)两个ip:port的数据包交互10.0.0.1:随机端口      >   10.0.0.7:22wireshark大鲨鱼抓包工具查看ssh登录数据包收发情况在window去登录 web-7ssh远程连接，也是建立的tcp/ip的三次握手之上2. 查看网站访问的数据包，基于 tcp/ip 基础之上的 HTTP应用层协议由于捕捉的是 vmnet8的网卡流量，检测http协议，只能给这个网段内的机器，发http请求这里需要注意，如果你多次访问nginx，你可能会抓不到默认的tcp三次握手tcp三次握手，是用于首次连接的访问nginx页面的请求，第一次以及建立好连接，默认会有一个保持连接你后续的请求，。就不会再继续tcp三次握手，而是直接发送http请求你和nginx服务器已经建立好tcp连接了。使用firefox另一个浏览器，重新去建立tcp连接</pre><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>通过wireshark工具查看</h3><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><img src="https://www.maxiaoke.com/uploads/images/20231227/7e1cda57cf9f9436f23bb997302da00d.png" alt=""/></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><img src="https://www.maxiaoke.com/uploads/images/20231227/cf2b08a712d2254d534fdd93970fc9b8.png" alt=""/></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><img src="https://www.maxiaoke.com/uploads/images/20231227/be7f6a95f29f863a4b0907c97fc2c9b7.png" alt=""/></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><img src="https://www.maxiaoke.com/uploads/images/20231227/047b5eccbed99cd728b54105323eea50.png" alt=""/></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 0px !important;"><img src="https://www.maxiaoke.com/uploads/images/20231227/31208141e08f9608070e98f32f656cac.png" alt=""/></p><p><br/></p><p><br/></p>

mysql数据库实战之详解DQL语句详细用法

后端
26713 阅读

<p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><span style="font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 1.75em; letter-spacing: 0.5px;">1.1、什么是DQL</span></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">DQL：数据查询语言，用于从数据库表中查询数据，并不会修改数据，只是一种显示数据的方式。由select语句构成。</p><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>1.2、记录查询格式</h3><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：select */字段列表 from 数据库表名 [where 条件表达式];</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">格式说明：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">select */字段列表：查询完后需要展示的字段</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">from 数据库表名：指定要查询的数据库表</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">[where 条件表达式]：查询满足条件的记录</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>二、记录查询</h2><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>2.1、简单查询</h3><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">查询表中的记录和列</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：select * from 数据库表名;   #查询表中所有记录,显示所有列或select 字段名1,字段名2,...,字段名n from 数据库表名;   #查询表中所有记录，显示指定列</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">案例：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">查询student表中的所有记录，显示所有列</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#显示所有记录mysql> select * from student;+------+-----------+------------+------+| id   | sname     | birthday   | sex  |+------+-----------+------------+------+| 1    | 郭德纲 | 1973-01-18 | 男  || 2    | 林志颖 | 1974-10-18 | 男  || 3    | 柳岩    | 1980-11-08 | 女  |+------+-----------+------------+------+3 行于数据集 (0.01 秒)</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">查询student表中的所有记录，显示所有姓名、性别列</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#显示所有记录,显示列为姓名、性别mysql> select sname,sex from student;+-----------+------+| sname     | sex  |+-----------+------+| 郭德纲 | 男  || 林志颖 | 男  || 柳岩    | 女  |+-----------+------+3 行于数据集 (0.01 秒)</pre><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>2.2、别名查询</h3><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">别名有二种：字段别名、表别名</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">作用：</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">字段别名查询出记录显示新的名字，并不影响表的结构。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">表别名取了一个新的名字，可以代替表名使用。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">字段别名</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：select 字段名1 as 别名1,字段名2 as 别名2,...,字段名n as 别名n from 数据库表名;</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">案例：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">查询student表中的sname和sex，以别名’姓名’和’性别’显示</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#使用字段别名显示姓名、性别mysql> select sname as 姓名,sex as 性别 from student;+-----------+------+| 姓名        | 性别   |+-----------+------+| 郭德纲 | 男  || 林志颖 | 男  || 柳岩    | 女  |+-----------+------+3 行于数据集 (0.01 秒)</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">表别名</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：select 字段名1 as 别名1,字段名2 as 别名2,...,字段名n as 别名n from 数据库表名 as 别名;</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">案例：</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">查询student表中的sname和sex，以别名’姓名’和’性别’显示，并为student表取了一个别名 s</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#使用字段别名显示姓名、性别，表别名没有具体表现mysql> select sname as 姓名,sex as 性别 from student as s;+-----------+------+| 姓名        | 性别   |+-----------+------+| 郭德纲 | 男  || 林志颖 | 男  || 柳岩    | 女  |+-----------+------+3 行于数据集 (0.01 秒)</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">注意：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">表别名一般用于多表查询，单表查询中没有具体体现。</p><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>2.3、清除重复记录查询</h3><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：select distinct 字段名 from 数据库表名;</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">案例：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">去掉性别重复的记录</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">去掉性别和姓名同时重复的记录</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#查看所有记录mysql> select * from student;+------+-----------+------------+------+| id   | sname     | birthday   | sex  |+------+-----------+------------+------+| 1    | 郭德纲 | 1973-01-18 | 男  || 2    | 林志颖 | 1974-10-18 | 男  || 3    | 柳岩    | 1980-11-08 | 女  |+------+-----------+------------+------+3 行于数据集 (0.01 秒)#查看sex不重复的记录mysql> select distinct sex from student;+------+| sex  |+------+| 男  || 女  |+------+2 行于数据集 (0.01 秒)#查看sex,sname都不重复的记录mysql> select distinct sex,sname from student;+------+-----------+| sex  | sname     |+------+-----------+| 男  | 郭德纲 || 男  | 林志颖 || 女  | 柳岩    |+------+-----------+3 行于数据集 (0.01 秒)</pre><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>2.4、运算查询</h3><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">字段与固定值运算</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：select 字段名+固定值 from 数据库表名;</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">注意：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">运算的字段必须是数值型</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">案例：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">查询student表中年龄减10岁，并显示sname和age</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">mysql> select age-10 as age ,sname from student;+-----+--------+| age | sname  |+-----+--------+|  37 | 郭德纲 ||  36 | 林志颖 ||  30 | 柳岩   |+-----+--------+3 rows in set</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">字段与字段运算</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：select 字段名+字段名 from 数据库表名;</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">注意：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">运算的字段必须是数值型</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">案例：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">查询student表中age与id的和，并显示出来age和id</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">mysql> select age+id,age,id from student;+--------+-----+----+| age+id | age | id |+--------+-----+----+|     48 |  47 |  1 ||     48 |  46 |  2 ||     43 |  40 |  3 |+--------+-----+----+3 rows in set</pre><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>三、条件查询</h2><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>3.1、条件查询前准备</h3><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">新建学生信息表（students）</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">字段：</strong>学生ID（sid）、学生姓名(sname)、学生性别(sex)、学生年龄(age)、英语成绩(english)、数学成绩(math)、入学时间(entertime)、备注(remark)</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">create table students(    sid int,    sname varchar(20),    sex varchar(2),    age int,    english double(4,1),    math double(4,1),    entertime date,    remark text);</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><img src="https://www.maxiaoke.com/uploads/images/20231229/86d18ea4c38a34028847b79e1fb1c7ac.png" alt=""/></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">记录：</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">insert into students values(1,'张三','男',19,98.5,88,'2017-09-01','他来自四川'),(2,'李四','男',20,80,88,'2017-09-01','他来自重庆'),(3,'张红','女',19,86,80,'2017-09-01','他来自北京'),(4,'张八','男',18,80,85,'2017-09-01','他来自天津'),(5,'李三','男',19,60,88,'2017-09-01','他来自湖北'),(6,'王六','女',20,50,70,'2017-09-01','他来自湖南'),(7,'刘红','女',18,90,98,'2017-09-01','他来自甘肃');</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><img src="https://www.maxiaoke.com/uploads/images/20231229/63b55469e767cf464a14ddd839d63aac.png" alt=""/></p>

Mysql数据库实战之详解DDL语句

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<p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">数据操纵语言DML（Data Manipulation Language），用户通过它可以实现对数据库的基本操作。就是我们最经常用到的UPDATE、INSERT、DELETE。主要用来对数据库的数据进行一些操作。</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>一、表记录操作-上</h2><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>1.1、DML概述</h3><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">DML 操作是指对数据库中表记录的操作，主要包括表记录的插入（insert）、更新（update）和删除（delete），是开发人员日常使用最频繁的操作。</p><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>1.2、插入记录</h3><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：insert into 数据库表名 [字段名列表] values(字段值列表)</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">说明：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">insert into 数据库表名：</strong>指定增加记录的表</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">[字段名列表]：</strong>表示要给那些字段加入字段值，没有，就为所有字段</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">values（字段值列表）：</strong>表示为对应的字段加入对应的字段值</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">为所有字段插入值</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：insert into 数据库表名(字段名1,字段名2...,字段名n)values(字段值1,字段值2...,字段值n);或insert into 数据库表名 values(字段值1,字段值2...,字段值n);</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">案例：</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#指定所有字段插入记录mysql> insert into student(id,sname,birthday)values(1,"林志颖","1974-10-18");Query OK, 1 rows affected (0.03 秒)#不指定字段，默认所有字段插入记录mysql> insert into student values(2,"郭德纲","1973-01-18");Query OK, 1 rows affected (0.01 秒)#查看数据库表中所有记录mysql> select * from student;+------+-----------+------------+| id   | sname     | birthday   |+------+-----------+------------+| 1    | 林志颖 | 1974-10-18 || 2    | 郭德纲 | 1973-01-18 |+------+-----------+------------+2 行于数据集 (0.01 秒)</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">插入部分字段值</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：insert into 数据库表名(字段名1,字段名2...)values(字段值1,字段值2...);#注意：没有给定字段的值，为null;</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">案例：</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#插入部分字段值mysql> insert into student(id,sname)values(3,"柳岩");Query OK, 1 rows affected (0.01 秒)#查看数据库表中所有记录mysql> select * from student;+------+-----------+------------+| id   | sname     | birthday   |+------+-----------+------------+| 1    | 林志颖 | 1974-10-18 || 2    | 郭德纲 | 1973-01-18 || 3    | 柳岩    | NULL       |+------+-----------+------------+3 行于数据集 (0.01 秒)</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">注意：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">只插入部份字段值时，前面必须带字段名字。</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">mysql> insert into student values(4,"王宝强");Column count doesn't match value count at row 1#列计数与第1行的值计数不匹配</pre><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>二、表记录操作-下</h2><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>2.1、更新记录</h3><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：update 数据库表名 set 字段名1=字段值1,字段名2=字段值2...,字段名n=字段值n [where 条件表达式];#注意：更新的数据可以是0-N条记录</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">说明：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">update 数据库表名：</strong>指定需要更新的数据库表</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">set 字段名=字段值：</strong>修改指定的数据库表中字段的值</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">[where 条件表达式]：</strong>修改满足条件的记录的字段值，可省略</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">不带条件记录更新</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：update 数据库表名 set 字段名1=字段值1,字段名2=字段值2...,字段名n=字段值n;  #表示修改表中所有记录</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">案例：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">加入一个性别（sex varchar(2)）字段，将sex的值都改为“男”</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#在student表中增加字段sexmysql> alter table student add sex varchar(2);Query OK, 0 rows affected (0.24 秒)#查看表结构mysql> desc student;+----------+-------------+------+-----+---------+-------+| Field    | Type        | Null | Key | Default | Extra |+----------+-------------+------+-----+---------+-------+| id       | int(11)     | YES  |     | NULL    |       || sname    | varchar(20) | YES  |     | NULL    |       || birthday | date        | YES  |     | NULL    |       || sex      | varchar(2)  | YES  |     | NULL    |       |+----------+-------------+------+-----+---------+-------+4 行于数据集 (0.01 秒)#修改student表中sex字段的值为'男'mysql> update student set sex='男';Query OK, 3 rows affected (0.09 秒)#查看表中所有记录mysql> select * from student;+------+-----------+------------+------+| id   | sname     | birthday   | sex  |+------+-----------+------------+------+| 1    | 林志颖 | 1974-10-18 | 男  || 2    | 郭德纲 | 1973-01-18 | 男  || 3    | 柳岩    | NULL       | 男  |+------+-----------+------------+------+3 行于数据集 (0.01 秒)</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">带条件记录更新</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：update 数据库表名 set 字段名1=字段值1,字段名2=字段值2...,字段名n=字段值n [where 条件表达式];   #表示修改表中满足条件的记录</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">案例：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">修改id=3的记录，将sex改为’女’</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#修改id为3记录中的sex改为'女'mysql> update student set sex='女' where id=3;Query OK, 1 rows affected (0.01 秒)#查看表中所有记录mysql> select * from student;+------+-----------+------------+------+| id   | sname     | birthday   | sex  |+------+-----------+------------+------+| 1    | 林志颖 | 1974-10-18 | 男  || 2    | 郭德纲 | 1973-01-18 | 男  || 3    | 柳岩    | NULL       | 女  |+------+-----------+------------+------+3 行于数据集 (0.01 秒)</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">修改id=3的记录，将sex改为’女’，birthday改为1980-11-08</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#修改id为3记录中的sex改为'女',birthday改为1980-11-08mysql> update student set sex='女',birthday='1980-11-08' where id=3;Query OK, 1 rows affected (0.11 秒)#查看表中所有记录mysql> select * from student;+------+-----------+------------+------+| id   | sname     | birthday   | sex  |+------+-----------+------------+------+| 1    | 林志颖 | 1974-10-18 | 男  || 2    | 郭德纲 | 1973-01-18 | 男  || 3    | 柳岩    | 1980-11-08 | 女  |+------+-----------+------------+------+3 行于数据集 (0.01 秒)</pre><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>2.2、删除记录</h3><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：delete from 数据库表名 [where 条件表达式];</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">说明：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">delete from 数据库表名：</strong>指定删除记录的表</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">[where 条件表达式]：</strong>删除满足条件的记录的字段值，可省略</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">带条件删除记录</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：delete from 数据库表名 [where 条件表达式]; #删除满足条件的记录</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">案例：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">删除id为1的记录</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#删除id=1的记录mysql> delete from student where id=1;Query OK, 1 rows affected (0.08 秒)#查看所有记录mysql> select * from student;+------+-----------+------------+------+| id   | sname     | birthday   | sex  |+------+-----------+------------+------+| 2    | 郭德纲 | 1973-01-18 | 男  || 3    | 柳岩    | 1980-11-08 | 女  |+------+-----------+------------+------+2 行于数据集 (0.02 秒)</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">不带条件删除记录</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式：delete from 数据库表名;    #删除表中所有的记录或truncate table 数据库表名;   #删除表中所有的记录</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">案例：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">删除表中所有记录</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#删除所有记录mysql> delete from student;Query OK, 2 rows affected (0.08 秒)#查看所有记录mysql> select * from student;空的数据集 (0.01 秒)#删除所有记录mysql> truncate table student;Query OK, 0 rows affected (0.08 秒)#查看所有记录mysql> select * from student;空的数据集 (0.01 秒)</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">注意：</strong></p><p style="box-sizing: border-box; margin-top: 0px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap; margin-bottom: 0px !important;">truncate删除的是表的结构，再创建一张表；delete删除的是表的记录；</p><p><br/></p>

Linux服务器常用服务部署之keepalived服务部署

后端
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<h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;">一、什么是高可用</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">通过前面课程的学习，我们知道LVS、Nginx可以实现很多种不同类型的分发，我们还知道，集群系统存在的作用就是为了解决单点故障的问题。</p><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>LVS、Nginx集群的单点故障问题</h3><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">这个单点故障主要体现在两个方面</p><ul style="box-sizing: border-box; margin-bottom: 16px; padding: 0px 0px 0px 2em; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;" class=" list-paddingleft-2"><li><p style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">分发器宕机怎么处理？<br/>假如nginx服务器挂掉了，那么所有的服务也会跟着瘫痪。<br/>一种方法是人为监控，发现主分发器宕机后，立马登录备分发器，并给它分配虚ip。</p><p style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">另一种办法是用软件来替代人来监控，自动登录备分发器，分配虚ip。</p></li><li><p style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">数据服务器宕机怎么处理？<br/>分发器可以自动判断数据服务器的存活状态，不对宕机服务器要数据。</p></li></ul><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>二、Keepalived介绍</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">keepalived是使用C语言编写的路由热备软件，该项目主要目标是为linux系统提供简单高效的负载均衡及高可用解决方案。keepalived由一组检查器，根据服务器的健康状况动态的维护和管理服务器池，另外keepalived通过vrrp协议实现高可用架构，vrrp是路由灾备的实现基础。通过前面的课程我们知道，在lvs中只解决了真实服务器的单点故障，但是如果分发器也就是lvs主机发生故障的话，整个集群系统都会崩溃，所以我们需要keepalived来实现集群系统的高可用。我们可以部署两台或更多的分发器，仅有一台调度器做为主服务器，其它的做为备用，当主调度器发生故障时，keepalived可以自动将备用调度器升级为主调度器，从而实现整个集群系统的高负载，高可用。</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>三、vrrp协议</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">vrrp协议是为了静态路由环境下防止单点故障而设计的主从灾备协议，在主设备发生故障时业务自动切换至从设备，而这一切对于用户而言是透明的。vrrp将两台或多台设备虚拟成一个设备，对外仅提供一个虚拟的IP地址，这些设备在同一时刻仅有一台设备可有拥有该IP地址，而拥有该IP地址的设备就是主设备,其它的就是备用设备。主设备会不断发送自己的状态信息给备用设备，当备用设备接收不到主设备的状态信息时，多个备用设备会根据自身的优先级选择出新的主设备，并拥有所有的业务功能。vrrp协议需要为每个路由设备定义一个虚拟路由ID（VRID）以及优先，所有主备路由设备的VRID必须一样，这样才会被视为同一组设备，而优先级最高的设备就是主路由设备，VRID和优先级的范围为0-255之间的整数，数值越大优先级越高，如果优先级相等，则会对比IP地址，地址越大优先级越高</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>四、部署keepalived</h2><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">[root@lvs1 ~]# dnf install keepalived -y</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">配置文件说明</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap; margin-bottom: 0px !important;">[root@lvs1 ~]# vim /etc/keepalived/keepalived.conf! Configuration File for keepalivedglobal_defs {                    #全局配置    notification_email {        #指定keepalived在发生切换时需要发送email到的对象，一行一个        acassen@firewall.loc    #指定收件人邮箱        failover@firewall.loc        sysadmin@firewall.loc    }    notification_email_from Alexandre.Cassen@firewall.loc #指定发件人    smtp_server 192.168.200.1    #指定smtp服务器地址    smtp_connect_timeout 30        #指定smtp连接超时时间    router_id LVS_DEVEL            #此处注意router_id为负载均衡标识，在局域网内应该是唯一的。    vrrp_skip_check_adv_addr    vrrp_strict    vrrp_garp_interval 0    vrrp_gna_interval 0}vrrp_instance VI_1 {        #虚拟路由的标识符    state MASTER            #状态只有MASTER和BACKUP两种，并且要大写，MASTER为工作状态，BACKUP是备用状态    interface eth0            #通信所使用的网络接口  virtual_router_id 51    #虚拟路由的ID号，是虚拟路由MAC的最后一位地址  priority 100            #此节点的优先级，主节点的优先级需要比其他节点高  advert_int 1            #通告的间隔时间  authentication {        #认证配置                auth_type PASS        #认证方式        auth_pass 1111        #认证密码    }    virtual_ipaddress {        #虚拟ip地址,可以有多个地址，每个地址占一行，不需要子网掩码，同时这个ip 必须与我们在lvs 客户端设定的vip 相一致！        192.168.200.16        192.168.200.17        192.168.200.18    }}virtual_server 192.168.200.100 443 { #集群所使用的VIP和端口    delay_loop 6                    #健康检查间隔，单位为秒    lb_algo rr                        #lvs调度算法rr|wrr|lc|wlc|lblc|sh|dh    nat_mask 255.255.255.0            #VIP掩码    lb_kind NAT                        #负载均衡转发规则。一般包括DR,NAT,TUN 3种    persistence_timeout 50            #会话保持时间，会话保持，就是把用户请求转发给同一个服务器，不然刚在1上提交完帐号密码，就跳转到另一台服务器2上了    protocol TCP                    #转发协议，有TCP和UDP两种，一般用TCP，没用过UDP    real_server 192.168.200.100 443 { #真实服务器，包括IP和端口号        weight 1                    #权重        TCP_CHECK {                    #通过tcpcheck判断RealServer的健康状态            connect_timeout 3        #连接超时时间            nb_get_retry 3            #重连次数            delay_before_retry 3    #重连间隔时间            connect_port 23            #健康检查的端口的端口            bindto <ip>          }        HTTP_GET  {        #健康检测方式，可选有 SSL_GET、TCP_CHECK、HTTP_GET            url {                    #检查url，可以指定多个              path /        #检查的url路径              digest ff20ad2481f97b1754ef3e12ecd3a9cc  #需要检查到的内容。检查后的摘要信息。            }            url {              path /mrtg              digest 9b3a0c85a887a256d6939da88aabd8cd            }            url {              path /testurl3/test.jsp              digest 640205b7b0fc66c1ea91c463fac6334d            }            connect_timeout 3        #连接超时时间            nb_get_retry 3            #检测尝试几次            delay_before_retry 3    #检测的时间间隔        }    }}</pre><p><br/></p>

Linux服务器常用服务部署之FTP服务器搭建

后端
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<h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;">一、FTP介绍</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">FTP (File transfer protocol) 是TCP/IP 协议组中的协议之一。他最主要的功能是在服务器与客户端之间进行文件的传输。FTP就是实现两台计算机之间的拷贝，从远程计算机拷贝文件至自己的计算机上，称之为“下载（download）”文件。将文件从自己计算机中拷贝至远程计算机上，则称之为“上传（upload）”文件。这个古老的协议使用的是明码传输方式，且过去有相当多的安全危机历史。为了更安全的使用 FTP 协议，我们主要介绍较为安全但功能较少的 vsftpd(very secure File transfer protocol ) 这个软件。FTP是一个C/S类型的软件，FTP监听TCP端口号为21，数据端口为20。</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>二、应用场景</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">下载服务器：提供对外的下载服务</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">文件服务器：提供上传和下载服务</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>三、FTP的权限</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">FTP 服务器的功能除了单纯的进行文件的传输与管理之外，依据服务器软件的设定架构，它还可以提供几个主要的功能。：<br/>不同等级的用户身份：user, guest, anonymous<br/>FTP 服务器在默认的情况下，依据使用者登录的情况而分为三种不同的身份，分别是：</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">(1)本地用户：系统中真实存在的用户</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">(2)来宾, guest；</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">(3)匿名登录者, anonymous</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">这三种身份的用户在系统上面的权限差异很大！例如实体用户取得系统的权限比较完整，所以可以进行比较多的动作；至于匿名登录者，大概我们就仅提供他下载资源的能力而已，并不许匿名者使用太多主机的资源！当然，这三种人物因为权限的不同能够使用的【在线命令】自然也就不相同！</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>四、FTP的工作模式</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">FTP支持两种模式，一种方式叫做Standard (也就是 PORT方式，主动方式)，一种是 Passive (也就是PASV，被动方式)。 Standard模式 FTP的客户端发送 PORT 命令到FTP服务器。Passive模式FTP的客户端发送 PASV命令到 FTP Server。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">下面介绍一个这两种方式的工作原理：</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">Port模式FTP 客户端首先和FTP服务器的TCP 21端口建立连接，通过这个通道发送命令，客户端需要接收数据的时候在这个通道上发送PORT命令。 PORT命令包含了客户端用什么端口接收数据。在传送数据的时候，服务器端通过自己的TCP 20端口连接至客户端的指定端口发送数据。 FTP server必须和客户端建立一个新的连接用来传送数据。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">Passive模式在建立控制通道的时候和Standard模式类似，但建立连接后发送的不是Port命令，而是Pasv命令。FTP服务器收到Pasv命令后，随机打开一个高端端口（端口号大于1024）并且通知客户端在这个端口上传送数据的请求，客户端连接FTP服务器此端口，然后FTP服务器将通过这个端口进行数据的传送，这个时候FTP server不再需要建立一个新的和客户端之间的连接。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">很多防火墙在设置的时候都是不允许接受外部发起的连接的，所以许多位于防火墙后或内网的FTP服务器不支持PASV模式，因为客户端无法穿过防火墙打开FTP服务器的高端端口；而许多内网的客户端不能用PORT模式登陆FTP服务器，因为从服务器的TCP 20无法和内部网络的客户端建立一个新的连接，造成无法工作。</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>五、FTP安装部署</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">约定：本实验中使用过的机器为centos8.0_x86_64系统，IP地址192.168.11.16/24.请关闭防火墙和SELINUX。</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">vsftp安装[root@localhost ~]# dnf -y install vsftpd ftpvsftp开机启动[root@localhost ~]# systemctl enable vsftpdCreated symlink from /etc/systemd/system/multi-user.target.wants/vsftpd.service to /usr/lib/systemd/system/vsftpd.service.启动vsftp服务[root@localhost ~]# systemctl start vsftpd验证启动[root@localhost ~]# lsof -i :21COMMAND  PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAMEvsftpd  1951 root    4u  IPv6  32837      0t0  TCP *:ftp (LISTEN)</pre><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>六、FTP配置文件</h2><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>6.1）相关文件</h3><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">主配文件:/etc/vsftpd/vsftpd.conf</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">下载目录:/var/ftp/</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">FTP日志:/var/log/xferlog</p><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>6.2）主配文件详解</h3><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;"># Example config file /etc/vsftpd/vsftpd.conf## The default compiled in settings are fairly paranoid. This sample file# loosens things up a bit, to make the ftp daemon more usable.# Please see vsftpd.conf.5 for all compiled in defaults.## READ THIS: This example file is NOT an exhaustive list of vsftpd options.# Please read the vsftpd.conf.5 manual page to get a full idea of vsftpd's# capabilities.##匿名用户访问,YES是允许，NO是拒绝# Allow anonymous FTP? (Beware - allowed by default if you comment this out).anonymous_enable=NO## Uncomment this to allow local users to log in.# 本地用户登录,YES是允许，NO是拒绝.默认访问的是本地用户家目录，如果你开启了selinux# 请设置开启布尔值ftp_home_dir为ON# When SELinux is enforcing check for SE bool ftp_home_dirlocal_enable=YES##允许本地用户上传# Uncomment this to enable any form of FTP write command.write_enable=YES## Default umask for local users is 077. You may wish to change this to 022,# 上传的权限是022，使用的是umask权限。对应的目录是755，文件是644# if your users expect that (022 is used by most other ftpd's)local_umask=022## Uncomment this to allow the anonymous FTP user to upload files. This only# has an effect if the above global write enable is activated. Also, you will# obviously need to create a directory writable by the FTP user.# When SELinux is enforcing check for SE bool allow_ftpd_anon_write, allow_ftpd_full_access# 开启匿名用户上传功能，默认是拒绝的#anon_upload_enable=YES## Uncomment this if you want the anonymous FTP user to be able to create# new directories.# 开启匿名用户创建文件或文件夹权限#anon_mkdir_write_enable=YES## Activate directory messages - messages given to remote users when they# go into a certain directory.# 开启目录欢迎消息，一般对命令行登陆有效dirmessage_enable=YES## Activate logging of uploads/downloads.# 开启上传和下载日志记录功能xferlog_enable=YES##使用标准模式# Make sure PORT transfer connections originate from port 20 (ftp-data).connect_from_port_20=YES## If you want, you can arrange for uploaded anonymous files to be owned by# a different user. Note! Using "root" for uploaded files is not# recommended!# 声明匿名用户上传文件的所有者# 允许更改匿名用户上传文件的所有者#chown_uploads=YES#所有者为whoever#chown_username=whoever## You may override where the log file goes if you like. The default is shown# below.# 日志文件路径#xferlog_file=/var/log/xferlog## If you want, you can have your log file in standard ftpd xferlog format.# Note that the default log file location is /var/log/xferlog in this case.# 日志文件采用标准格斯xferlog_std_format=YES## You may change the default value for timing out an idle session.# 会话超时时间#idle_session_timeout=600## You may change the default value for timing out a data connection.# 数据传输超时时间#data_connection_timeout=120## It is recommended that you define on your system a unique user which the# ftp server can use as a totally isolated and unprivileged user.# FTP子进程管理用户#nopriv_user=ftpsecure## Enable this and the server will recognise asynchronous ABOR requests. Not# recommended for security (the code is non-trivial). Not enabling it,# however, may confuse older FTP clients.# 是否允许客户端发起“async ABOR”请求，该操作是不安全的默认禁止。#async_abor_enable=YES## By default the server will pretend to allow ASCII mode but in fact ignore# the request. Turn on the below options to have the server actually do ASCII# mangling on files when in ASCII mode. The vsftpd.conf(5) man page explains# the behaviour when these options are disabled.# Beware that on some FTP servers, ASCII support allows a denial of service# attack (DoS) via the command "SIZE /big/file" in ASCII mode. vsftpd# predicted this attack and has always been safe, reporting the size of the# raw file.# ASCII mangling is a horrible feature of the protocol.# 该选项用于指定是否允许上传时以ASCII模式传输数据#ascii_upload_enable=YES#该选项用于指定是否允许下载时以ASCII模式传输数据#ascii_download_enable=YES## You may fully customise the login banner string:# FTP文本界面登陆欢迎词#ftpd_banner=Welcome to blah FTP service.## You may specify a file of disallowed anonymous e-mail addresses. Apparently# useful for combatting certain DoS attacks.# 是否开启拒绝的Email功能#deny_email_enable=YES# (default follows)# 指定保存被拒接的Email地址的文件#banned_email_file=/etc/vsftpd/banned_emails## You may specify an explicit list of local users to chroot() to their home# directory. If chroot_local_user is YES, then this list becomes a list of# users to NOT chroot().# (Warning! chroot'ing can be very dangerous. If using chroot, make sure that# the user does not have write access to the top level directory within the# chroot)# 是否开启对本地用户chroot的限制，YES为默认所有用户都不能切出家目录，NO代表默认用户都可以切出家目录# 设置方法类似于：YES拒绝所有，允许个别    NO  允许所有拒绝个别#chroot_local_user=YES#开启特例列表#chroot_list_enable=YES# (default follows)# 如果chroot_local_user的值是YES则该文件中的用户是可以切出家目录，如果是NO，该文件中的用户则不能切出家目录# 一行一个用户。#chroot_list_file=/etc/vsftpd/chroot_list## You may activate the "-R" option to the builtin ls. This is disabled by# default to avoid remote users being able to cause excessive I/O on large# sites. However, some broken FTP clients such as "ncftp" and "mirror" assume# the presence of the "-R" option, so there is a strong case for enabling it.# 是否开启ls 递归查询功能 ls -R#ls_recurse_enable=YES## When "listen" directive is enabled, vsftpd runs in standalone mode and# listens on IPv4 sockets. This directive cannot be used in conjunction# with the listen_ipv6 directive.# 是否开启ftp独立模式在IPV4listen=NO## This directive enables listening on IPv6 sockets. By default, listening# on the IPv6 "any" address (::) will accept connections from both IPv6# and IPv4 clients. It is not necessary to listen on *both* IPv4 and IPv6# sockets. If you want that (perhaps because you want to listen on specific# addresses) then you must run two copies of vsftpd with two configuration# files.# Make sure, that one of the listen options is commented !!# 是否开启ftp独立模式在ipv6listen_ipv6=YES#启用pam模块验证pam_service_name=vsftpd#是否开启userlist功能.#是否启用用户列表功能userlist_enable=YES</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">通过配置文件的分析，VSFTP不允许匿名访问，本地用户可以下载和上传。如果允许匿名用户登录的话需要将anonymous_enable=YES，然后重新启动服务</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">我们可以通过修改配置文件的内容即可配置FTP的相关登陆情况。</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>七、FTP客户端访问</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">FTP是一个C/S类型的软件,连接服务端需要FTP客户端才能完成，常见的FTP客户端有以下几种:</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">浏览器：可以通过浏览器中输入 ftp://ip或者ftp://域名的方式来访问FTP</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">自带客户端:命令行下可以使用ftp命令去连接</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">三方客户端：FileZilla 8uftp 图形软件或者文本界面的lftp等</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">三种方式中，文本界面是比较麻烦的，无法鼠标流。所以我重点给大家讲解一下</p><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>7.1）文本界面登陆</h3><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">文本界面匿名登陆[root@localhost ~]# ftp 192.168.11.16Connected to 192.168.11.16 (192.168.11.16).220 (vsFTPd 3.0.3)Name (192.168.11.16:root): ftp    #用户名可以是ftp也可以是anonymous331 Please specify the password.Password:                            #密码为空230 Login successful. #显示登陆成功Remote system type is UNIX.Using binary mode to transfer files.ftp> ls227 Entering Passive Mode (192,168,11,16,90,35).150 Here comes the directory listing.drwxr-xr-x    2 0        0               6 May 14  2019 pub226 Directory send OK.通过ls可以列出当前目录下有哪些内容 看到有一个目录叫pubftp> pwd257 "/"   通过pwd命令查看当前路径  注意这里显示的是FTP的根目录ftp> bye221 Goodbye.退出使用bye命令文本界面本地用户登录[root@localhost ~]# ftp 192.168.11.16Connected to 192.168.11.16 (192.168.11.16).220 (vsFTPd 3.0.3)Name (192.168.11.16:root): hello331 Please specify the password.Password:230 Login successful.Remote system type is UNIX.Using binary mode to transfer files.ftp> ls227 Entering Passive Mode (192,168,11,16,130,240).150 Here comes the directory listing.drwxr-xr-x    2 1001     1001            6 Jan 15 08:56 下载drwxr-xr-x    2 1001     1001            6 Jan 15 08:56 公共drwxr-xr-x    2 1001     1001            6 Jan 15 08:56 图片drwxr-xr-x    2 1001     1001            6 Jan 15 08:56 文档drwxr-xr-x    2 1001     1001            6 Jan 15 08:56 桌面drwxr-xr-x    2 1001     1001            6 Jan 15 08:56 模板drwxr-xr-x    2 1001     1001            6 Jan 15 08:56 视频drwxr-xr-x    2 1001     1001            6 Jan 15 08:56 音乐226 Directory send OK.ftp> pwd257 "/home/hello" is the current directory</pre><h3 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.43; font-size: 1.5em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>7.2）FTP客户端常用命令</h3><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">键入help命令可以查看所有可使用的命令ftp> helpCommands may be abbreviated.  Commands are:!                debug         mdir           sendport     site$                dir           mget           put          sizeaccount          disconnect    mkdir          pwd          statusappend           exit          mls            quit         structascii            form          mode           quote        systembell             get           modtime        recv         suniquebinary           glob          mput           reget        tenexbye              hash          newer          rstatus      tickcase             help          nmap           rhelp        tracecd               idle          nlist          rename       typecdup             image         ntrans         reset        userchmod            lcd           open           restart      umaskclose            ls            prompt         rmdir        verbosecr               macdef        passive        runique        ?delete           mdelete       proxy          send!+linux命令   执行系统命令!ls /opt  显示linux系统中/opt目录下的内容ftp> !ls /optdhcp  dns  rhlcd linux系统中的当前目录lcd /root  将linux系统中的当前目录切换到/root下ftp> lcd /rootLocal directory now /rootput 上传命令，mput批量上传命令上传initial-setup-ks.cfg文件到hello家目录下ftp> put initial-setup-ks.cfg local: initial-setup-ks.cfg remote: initial-setup-ks.cfg227 Entering Passive Mode (192,168,11,16,96,132).150 Ok to send data.226 Transfer complete.1803 bytes sent in 0.00135 secs (1333.58 Kbytes/sec)可以看到上传成功了验证一下上传结果ftp> ls227 Entering Passive Mode (192,168,11,16,173,142).150 Here comes the directory listing.-rw-r--r--    1 1000     1000         1803 Feb 26 07:01 initial-setup-ks.cfgdrwxr-xr-x    2 1000     1000            6 Jan 11 01:37 下载drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 公共drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 图片drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 文档drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 桌面drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 模板drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 视频drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 音乐226 Directory send OK.看见了吧切换linux当前目录到/tmpftp> lcd /tmpLocal directory now /tmpget下载命令，mget批量下载下载initial-setup-ks.cfg到linux系统当前目录/tmpftp> get initial-setup-ks.cfglocal: initial-setup-ks.cfg remote: initial-setup-ks.cfg227 Entering Passive Mode (192,168,11,16,229,134).150 Opening BINARY mode data connection for initial-setup-ks.cfg (1803 bytes).226 Transfer complete.1803 bytes received in 2.9e-05 secs (62172.41 Kbytes/sec)列出linux目录/tmp的内容，看到了下载的文件initial-setup-ks.cfgftp> !ls /tmp/dhcp                                          tracker-extract-files.0initial-setup-ks.cfg                                  VMwareDnDsystemd-private-8e7a99ea89c14ab396d66116970fe04d-chronyd.service-sghHHs       vmware-rootsystemd-private-8e7a99ea89c14ab396d66116970fe04d-colord.service-wK7h08      yum_save_tx.2019-02-20.16-10.Z6uXqR.yumtxsystemd-private-8e7a99ea89c14ab396d66116970fe04d-cups.service-cokBro          yum_save_tx.2019-02-21.09-03.08zIbU.yumtxsystemd-private-8e7a99ea89c14ab396d66116970fe04d-rtkit-daemon.service-6wt1S0  yum_save_tx.2019-02-22.11-10.prawAT.yumtxftp> close221 Goodbye.ftp> lsNot connected.可以使用close断开连接，当连接断开希望再次连接直接使用open命令即可ftp> open 192.168.11.16Connected to 192.168.11.16 (192.168.11.16).220 (vsFTPd 3.0.2)Name (192.168.11.16:root): hello331 Please specify the password.Password:230 Login successful.Remote system type is UNIX.Using binary mode to transfer files.ftp> ls227 Entering Passive Mode (192,168,11,16,192,88).150 Here comes the directory listing.-rw-r--r--    1 1000     1000         1803 Feb 26 07:01 initial-setup-ks.cfgdrwxr-xr-x    2 1000     1000            6 Jan 11 01:37 下载drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 公共drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 图片drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 文档drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 桌面drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 模板drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 视频drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 音乐226 Directory send OK.delete命令可以删除属于自己的文件删除initial-setup-ks.cfg文件ftp> delete initial-setup-ks.cfg250 Delete operation successful.ftp> ls227 Entering Passive Mode (192,168,11,16,168,142).150 Here comes the directory listing.drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 下载drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 公共drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 图片drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 文档drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 桌面drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 模板drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 视频drwxr-xr-x    2 1000     1000            6 Jan 11 01:37 音乐226 Directory send OK.</pre><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>八、基于虚拟用户配置安全的ftp</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">在ftp中不论是匿名用户还是实名用户都是系统中真实存在的用户，或多或少都会有一些安全方面的风险，为了避免这个风险，开发者在ftp中加入了一个虚拟用户的概念，所有虚拟用户都会被统一映射为一个系统账号，免去了管理过多账户的麻烦，那么这个虚拟用户如何实现呢？</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap; margin-bottom: 0px !important;">a、修改配置文件 [root@zutuanxue pam.d]# egrep -v "^#" /etc/vsftpd/vsftpd.conf anonymous_enable=YESlocal_enable=YESwrite_enable=YESlocal_umask=022dirmessage_enable=YESxferlog_enable=YESconnect_from_port_20=YESxferlog_std_format=YESchroot_local_user=YESlisten=NOlisten_ipv6=YES#虚拟用户配置选项#pam登陆验证pam_service_name=vftp#允许虚拟用户功能guest_enable=YES#虚拟用户映射到本地用户helloguest_username=hello#这里我通过指令改变了默认设置，允许虚拟用户写allow_writeable_chroot=YES #本地用户的根目录#这里是定义虚拟用户主目录，用户和组必须指定为宿主用户hellolocal_root=/home/hello#允许虚拟用户和本地用户权限一致virtual_use_local_privs=YES#如果虚拟用户和本地用户权限不同，可以通过以下的指令来设置指令，配置文件和登陆名同步即可。#user_config_dir=/etc/vsftpd/vconf.d/b、生成虚拟用户账号密码文件奇数行数账户，偶数行是密码[root@zutuanxue ~]# cat /etc/vsftpd/vuservuser01123456vuser02123456使用db_load转成db格式[root@zutuanxue ~]# db_load -T -t hash -f /etc/vsftpd/vuser /etc/vsftpd/vuser.db要求权限是600[root@zutuanxue ~]# chmod 600 /etc/vsftpd/vuser.dbc、配置pam认证，注意先后顺序[root@zutuanxue ~]# cat /etc/pam.d/vftp #虚拟用户登录auth       sufficient     /lib64/security/pam_userdb.so db=/etc/vsftpd/vuseraccount    sufficient     /lib64/security/pam_userdb.so db=/etc/vsftpd/vuser#本地登陆session    optional     pam_keyinit.so    force revokeauth       required    pam_listfile.so item=user sense=deny file=/etc/vsftpd/ftpusers onerr=succeedauth       required    pam_shells.soauth       include    password-authaccount    include    password-authsession    required     pam_loginuid.sosession    include    password-authd、重启服务生效[root@zutuanxue ~]# systemctl restart vsftpd[root@zutuanxue ~]# cat /etc/vsftpd/chroot_list vuser01vuser02e、验证登陆[root@zutuanxue ~]# ftp 192.168.11.16Connected to 192.168.11.16 (192.168.11.16).220 Welcome to ayitula FTP service.Name (192.168.11.16:root): vuser01331 Please specify the password.Password:230 Login successful.Remote system type is UNIX.Using binary mode to transfer files.ftp> ls227 Entering Passive Mode (192,168,11,16,82,91).150 Here comes the directory listing.226 Transfer done (but failed to open directory).登陆成功了.</pre><p><br/></p>

详细介绍Apache服务器优化之长连接优化

后端
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<h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;">一、长连接介绍</h2><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a><strong style="box-sizing: border-box;">面临问题：</strong></h4><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">http是一个面向连接的协议，用户完成一次请求需要以下步骤</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">三次握手</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">发起请求</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">响应请求</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">四次断开</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">N个请求就重复N次，如果希望用户能够更快的拿到数据，服务器的压力降到最低，让你去优化这个请求过程。</p><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a><strong style="box-sizing: border-box;">解决方案：</strong></h4><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">答案很明确，那就是建设每次执行的三次握手和四次断开，最好是一次三次握手建立成功后，在这个数据通道完成所有的请求后，然后在四次断开，这就是优化思路–理想中应该是这样。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">三次握手</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">发起请求</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">响应请求</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">发起请求</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">响应请求</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">。。。。。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">请求全部完成后，四次断开</p><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a><strong style="box-sizing: border-box;">优化目的：</strong></h4><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">减少了三次握手和四次断开的次数。</p><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>注意事项：</h4><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">长连接需要服务器和客户端浏览器都支持</p><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>长连接特点：</h4><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">提升用户访问速度</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">降低服务器压力</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">大量空闲长连接可能造成服务器压力过大</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>二、长连接实现</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">apache2.4默认开启了长连接，长连接时间为5s，修改子配置文件httpd-default.conf可以定义该选项</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">#开启长连接功能 On为开启 Off为关闭</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">KeepAlive On</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">#当keepalive打开时，maxkeepaliverequests指令限制每个连接允许的请求数。如果设置为0，则允许无限请求。我们建议将此设置保持为高值以获得最大服务器性能。不建议大家将这个数值设置为0，防止内存溢出。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">MaxKeepAliveRequests 100</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">长连接时间，默认单位是秒，也可以使用ms 只需在数值后面添加单位就行了。这个值如果你服务器速度快，网络稳定，建议设置小一点，比如3s，因为目前单个请求都是毫秒级的。避免大量空闲长连接消耗你的系统资源。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">KeepAliveTimeout 5</p><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>实验总结：</h4><p style="box-sizing: border-box; margin-top: 0px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap; margin-bottom: 0px !important;">一次用户访问的长连接数根据用户浏览器的不同建立的数量不同，比如chrome,每次会同时建立5个长连接，也就是五个数据通道，然后完成数据请求，所以大家都反应chrome浏览器好用，其他浏览器要看情况，不同浏览器的连接数不同。</p><p><br/></p>

lamp环境安装部署之php平台集成

后端
11931 阅读

<h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238);">一、平台集成</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">单个软件是无法直接完成我们发布PHP站点的既定任务的，需要我们通过多个软件的通力合作才可以完成，所以我们需要将多个软件关联起来，让彼此各司其职，各干其活。一起完成我们的工作。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">linux：系统软件，应用软件平台</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">apache：接受用户请求，处理静态数据，响应用户请求</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">php：处理用户的PHP请求</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">mysql：存储数据</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238);"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>二、平台集成方法</h2><ul style="box-sizing: border-box; margin-bottom: 16px; padding: 0px 0px 0px 2em;" class=" list-paddingleft-2"><li><p>PHP作为模块</p></li><li><p>PHP作为服务</p></li></ul><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>1.PHP作为模块</h4><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">这种方式是历史最悠久的关联方法，PHP模块默认出于休眠状态，和apache是上下级关系。apache接受了用户PHP请求后去唤醒PHP模块，PHP模块再去处理请求。</p><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>2.PHP作为服务</h4><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">这种是apache2.4新增功能，PHP是一个服务，常驻内存。和apache是平级关系，apache接受了用户请求直接通过socket或tcp/ip的方式发送给PHP服务，PHP服务直接处理。如果是在同一台机器安装了apache和php建议使用socket方式关联，系统开销最小，并发更大。</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238);"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>三、PHP作为模块</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">[root@zutuanxue php-7.3.4]# ./configure —prefix=/usr/local/php —with-config-file-path=/usr/local/php/etc —with-mysqli=mysqlnd —enable-pdo —with-pdo-mysql=mysqlnd —with-iconv-dir=/usr/local/ —enable-fpm —with-fpm-user=www —with-fpm-group=www —with-pcre-regex —with-zlib —with-bz2 —enable-calendar —disable-phar —with-curl —enable-dba —with-libxml-dir —enable-ftp —with-gd —with-jpeg-dir —with-png-dir —with-zlib-dir —with-freetype-dir —enable-gd-jis-conv —with-mhash —enable-mbstring —enable-opcache=yes —enable-pcntl —enable-xml —disable-rpath —enable-shmop —enable-sockets —enable-zip —enable-bcmath —with-snmp —disable-ipv6 —with-gettext —disable-rpath —disable-debug —enable-embedded-mysqli —with-mysql-sock=/usr/local/mysql/<strong style="box-sizing: border-box;"> —with-apxs2=/usr/local/apache2/bin/apxs</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">在PHP编译的时候需要加上–with-apxs2=/usr/local/apache2/bin/apxs语句，意思是通过apache的apxs命令将PHP生成为一个apache模块。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">配置方法</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">apache修改主配置文件，添加以下行Include conf/extra/php.conf[root@zutuanxue conf]# cat extra/php.conf LoadModule php7_module        modules/libphp7.soAddType application/x-httpd-php .php<VirtualHost *:80>    DocumentRoot "/usr/local/apache/htdocs/web1"</VirtualHost><Directory "/usr/local/apache/htdocs/web1">    Options Indexes FollowSymLinks    AllowOverride None    Require all granted</Directory><IfModule dir_module>    DirectoryIndex index.php index.html</IfModule></pre><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238);"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>四、PHP作为服务</h2><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>tcp sock 模式</h4><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">1）修改apache子配置文件apache修改主配置文件，添加以下行Include conf/extra/php-fpm.conf[root@zutuanxue conf]# cat extra/php-fpm.confLoadModule proxy_module modules/mod_proxy.soLoadModule proxy_fcgi_module modules/mod_proxy_fcgi.so2）设置虚拟主机 关联php<VirtualHost *:80>    DocumentRoot "/usr/local/apache/htdocs/web1"</VirtualHost><Directory "/usr/local/apache/htdocs/web1">    Options Indexes FollowSymLinks    AllowOverride None    Require all granted</Directory><IfModule dir_module>    DirectoryIndex index.php index.html</IfModule><FilesMatch \.php$>         SetHandler "proxy:fcgi://127.0.0.1:9000"</FilesMatch></pre><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>unix sock模式</h4><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">1）apache修改主配置文件，添加以下行Include conf/extra/php-fpm.conf[root@zutuanxue conf]# cat extra/php-fpm.confLoadModule proxy_module modules/mod_proxy.soLoadModule proxy_fcgi_module modules/mod_proxy_fcgi.so2）修改PHP-FPM配置文件[root@zutuanxue extra]# egrep "^listen" /usr/local/php/etc/php-fpm.d/www.conflisten = /usr/local/php/etc/php-fpm.socketlisten.backlog = 511#设置UNIX socket 权限listen.owner = www     listen.group = wwwlisten.mode = 06603）设置虚拟主机 关联php-fpm<VirtualHost *:80>    DocumentRoot "/usr/local/apache/htdocs/web1"<FilesMatch "\.php$">    # Unix sockets require 2.4.7 or later    SetHandler  "proxy:unix:/usr/local/php/etc/php-fpm.socket|fcgi://localhost/"</FilesMatch></VirtualHost></pre><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238);"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>五、测试页面</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">1）生成测试页面</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">echo “<?php phpinfo(); ?>” /DR/phpinfo.php</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">2）测试</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">打开浏览器输入</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><a href="http://xn--ip-on6cx8lt2pxx7b/phpinfo.php" style="box-sizing: border-box; color: rgb(51, 202, 187); text-decoration-line: none; background: transparent; transition: all 0.3s linear 0s; outline: none !important;">http://ip或者域名/phpinfo.php</a></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 0px !important;"><img src="https://www.maxiaoke.com/uploads/images/20231230/1558e115d620e5ce62cfb2db4f85f083.png" alt=""/></p><p><br/></p>

详解讲解shell脚本编程之与用户输入交互

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<p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">学会了输出，那么输出什么呢？当然是人类让计算机运算的数据，那么运算的数据来自哪里？</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">可以肯定是你或其他人给的，那如何给程序数据呢？</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><strong style="box-sizing: border-box;">那么我们就得看看如何实现人机交互了。</strong></p><ul style="box-sizing: border-box; margin-bottom: 16px; padding: 0px 0px 0px 2em;" class=" list-paddingleft-2"><li><p>比如计算机程序</p></li><li><p>比如信息录入系统</p></li></ul><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238);"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>一、read命令</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;">功能：默认接受键盘的输入，回车符代表输入结束<br/>应用场景：人机交互<br/>命令选项</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">-p打印信息-t限定时间-s不回显-n输入字符个数</pre><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238);"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background: transparent; transition: all 0.3s linear 0s; outline: none !important;"></a>二、交互输入案例</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><strong style="box-sizing: border-box;">案例需求：</strong><br/>写一个系统用户交互登录界面脚本，仿linux文本界面登录<br/><strong style="box-sizing: border-box;">案例要点：</strong><br/>了解linux文本界面登陆所需要的输出信息及界面布局</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><img src="https://www.maxiaoke.com/uploads/images/20231230/fb6b82682d96cc2d9f6eca6cd7ca212e.gif" alt=""/></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><strong style="box-sizing: border-box;">job实现步骤：</strong><br/>1、根据linux文本界面登陆窗口输出信息，打印登陆提示信息<br/>2、交互输入登陆账号<br/>3、交互输入登陆密码</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><strong style="box-sizing: border-box;">代码实现：</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">#job实现代码   02_login.sh#!/bin/bash# #Author: www.zutuanxue.com#Release: #Description: 仿真登陆IP=`ifconfig ens33|egrep -w "inet"|awk '{print $2}'`#1、清屏clear#2、输出提示信息echo "CentOS Linux 8 (Core)"echo -e "Kernel `uname -r` on an `uname -m`\n"echo -e "Web console: https://localhost:9090/ or https://$IP:9090/ \n"#3、交互输入登陆名echo -n "$HOSTNAME login: "read account#4、交互输入密码read -s -t30 -p "Password: " pwecho</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px;"><strong style="box-sizing: border-box;">实现效果：</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 0px !important;"><img src="https://www.maxiaoke.com/uploads/images/20231230/814f705a3462f8c426faf3550eec5896.gif" alt=""/></p><p><br/></p><p><br/></p>

shell脚本编程之格式化输出

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<p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">计算机程序其实就是三步:输入、运算、输出，这个理论也适应于shell编程。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">那么计算机是如何将信息按照比较舒服的格式输出到屏幕或者KFC的打印纸上的呢！如果让计算机能够输出一种格式，让人看起来很舒服，那么我们就要学习一下计算机的格式化输出，让计算机程序将信息输出的时候美美哒！让人一目了然看到需要的信息。</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>一、shell格式化输出</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">一个赏心悦目的界面是一个程序给用户的第一个映像，好的界面可以让用户更加容易上手使用。windows之所以能被个人用户喜欢就是因为它的界面更加容易和用户交互，只要用户能识别文字，懂得点击鼠标就能操作电脑；而linux之所以无法被广大个人用户使用的瓶颈就是图形界面无法完成所有工作，需要命令配合才可以，这就把非专业用户拒之门外了，想用就必须去学习命令。<br/>我们在使用shell写一个程序的时候，如果想让广大的用户都能使用，都能快速上手，那么好的交互界面就太重要了。我们可以使用多种方法开发好的、易交互的界面，常用的工具有：dialog、echo、printf等命令。<br/>本节课主要给大家介绍一个最简单易用的命令：echo</p><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>1、echo命令</h4><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">功能：将内容输出到默认显示设备</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><strong style="box-sizing: border-box;">应用场景：需要计算机程序输出的地方</strong></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">echo命令的功能是在显示器上显示一段文字，一般起到一个提示的作用。功能说明:显示文字。</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">语法:echo [-ne][字符串]补充说明:1、echo会将输入的字符串送往标准输出。2、输出的字符串间以空白字符隔开,并在最后加上换行号。OPTIONS：-n    不要在最后自动换行-e    若字符串中出现以下字符，则特别加以处理，而不会将它当成一般文字输出:转义字符\a    发出警告声;\b    删除前一个字符;\t    插入tab;\n    换行且光标移至行首;\c    最后不加上换行符号;\f    换行但光标仍旧停留在原来的位置;\r    光标移至行首，但不换行;\v    与\f相同;\        插入\字符;\0nnn    打印nnn(八进制)所代表的ASCII字符;  备注：数字0  不要理解成字母o\xNN  打印NN(十六进制)所代表的ASCII字符;-–help    显示帮助-–version显示版本信息你的进制转换过关吗？[root@zutuanxue ~]# echo -e "\0123"   #ot(123) = 83  对应ascii表的SS[root@zutuanxue ~]# echo -e "\x61"   #ox(61) = 97  对应ascii表的aa</pre><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>2、输出颜色字体</h4><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">脚本中echo显示内容带颜色显示,echo显示带颜色，<strong style="box-sizing: border-box;">需要使用参数-e</strong></p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">格式如下：echo -e "\033[字背景颜色；文字颜色m字符串\033[0m"</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">例如： echo -e “\033[41;36m something here \033[0m”</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">其中41的位置代表底色， 36m的位置是代表字的颜色</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">1、字背景颜色和文字颜色之间是英文的</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">2、文字颜色后面有个m</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">3、字符串前后可以没有空格，如果有的话，输出也是同样有空格</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">下面是相应的字和背景颜色，可以自己来尝试找出不同颜色搭配　　例　　echo -e “\033[31m 红色字 \033[0m”　　echo -e “\033[34m 黄色字 \033[0m”　　echo -e “\033[41;33m 红底黄字 \033[0m”　　echo -e “\033[41;37m 红底白字 \033[0m”　　字颜色：30—–37　　echo -e “\033[30m 黑色字 \033[0m”　　echo -e “\033[31m 红色字 \033[0m”　　echo -e “\033[32m 绿色字 \033[0m”　　echo -e “\033[33m 黄色字 \033[0m”　　echo -e “\033[34m 蓝色字 \033[0m”　　echo -e “\033[35m 紫色字 \033[0m”　　echo -e “\033[36m 天蓝字 \033[0m”　　echo -e “\033[37m 白色字 \033[0m”　　字背景颜色范围：40—–47　　echo -e “\033[40;37m 黑底白字 \033[0m”　　echo -e “\033[41;37m 红底白字 \033[0m”　　echo -e “\033[42;37m 绿底白字 \033[0m”　　echo -e “\033[43;37m 黄底白字 \033[0m”　　echo -e “\033[44;37m 蓝底白字 \033[0m”　　echo -e “\033[45;37m 紫底白字 \033[0m”　　echo -e “\033[46;37m 天蓝底白字 \033[0m”　　echo -e “\033[47;30m 白底黑字 \033[0m”　　最后面控制选项说明　　\033[0m 关闭所有属性　　\033[1m 设置高亮度　　\033[4m 下划线　　\033[5m 闪烁　　\033[7m 反显　　\033[8m 消隐　　\033[30m — \33[37m 设置前景色　　\033[40m — \33[47m 设置背景色　　　　　　\033[nA 光标上移n行　　\033[nB 光标下移n行　　\033[nC 光标右移n行　　\033[nD 光标左移n行　　\033[y;xH设置光标位置　　\033[2J 清屏　　\033[K 清除从光标到行尾的内容　　\33[s 保存光标位置　　\033[u 恢复光标位置　　\033[?25l 隐藏光标　　\033[?25h 显示光标　　用法例子  光标下移三行　　[root@zutuanxue ~]# echo -e "\033[0m today is fine \033[3B" today is fine</pre><h4 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 16px; font-weight: 300; line-height: 1.4; font-size: 1.25em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>3、jobs</h4><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">需求：输出一个水果购物界面 fruits_shop.sh</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><img src="https://www.maxiaoke.com/uploads/images/20231230/714fbb7050a1799d29ae48a8c1de45d2.png" alt=""/></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">案例要点：</p><ul style="box-sizing: border-box; margin-bottom: 16px; padding: 0px 0px 0px 2em; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;" class=" list-paddingleft-2"><li><p>echo输出缩进问题</p></li><li><p>字体颜色输出</p></li></ul><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">代码实现：</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap; margin-bottom: 0px !important;">job代码    01_fruits_shop.sh#!/bin/bash# #Author: www.zutuanxue.com#Release: #Description:打印水果超市列表echo -e "\t\t    \033[32m Fruits List \033[0m      \n"echo -e "\t   \033[31mFruit\033[0m   \t\t \033[31mPrice\033[0m \t\t\033[31mWeight\033[0m"echo -e "\t\033[34m1)Apple\t\t￥10.00\t\t1KG\033[0m"echo -e "\t\033[34m2)Banana\t￥9.00\t\t1KG\033[0m"echo -e "\t\033[34m3)Orange\t￥15.20\t\t1KG\033[0m"</pre><p><br/></p>

深入解析go语言中的map数据类型实现原理

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<p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">Go中的map在底层是用哈希表实现的，你可以在 $GOROOT/src/pkg/runtime/hashmap.goc 找到它的实现。</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>数据结构</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">哈希表的数据结构中一些关键的域如下所示：</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">struct Hmap{    uint8   B;    // 可以容纳2^B个项    uint16  bucketsize;   // 每个桶的大小    byte    *buckets;     // 2^B个Buckets的数组    byte    *oldbuckets;  // 前一个buckets，只有当正在扩容时才不为空};</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">上面给出的结构体只是Hmap的部分的域。需要注意到的是，这里直接使用的是Bucket的数组，而不是Bucket*指针的数组。这意味着，第一个Bucket和后面溢出链的Bucket分配有些不同。第一个Bucket是用的一段连续的内存空间，而后面溢出链的Bucket的空间是使用mallocgc分配的。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">这个hash结构使用的是一个可扩展哈希的算法，由hash值mod当前hash表大小决定某一个值属于哪个桶，而hash表大小是2的指数，即上面结构体中的2^B。每次扩容，会增大到上次大小的两倍。结构体中有一个buckets和一个oldbuckets是用来实现增量扩容的。正常情况下直接使用buckets，而oldbuckets为空。如果当前哈希表正在扩容中，则oldbuckets不为空，并且buckets大小是oldbuckets大小的两倍。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">具体的Bucket结构如下所示：</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">struct Bucket{    uint8  tophash[BUCKETSIZE]; // hash值的高8位....低位从bucket的array定位到bucket    Bucket *overflow;           // 溢出桶链表，如果有    byte   data[1];             // BUCKETSIZE keys followed by BUCKETSIZE values};</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">其中BUCKETSIZE是用宏定义的8，每个bucket中存放最多8个key/value对, 如果多于8个，那么会申请一个新的bucket，并将它与之前的bucket链起来。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">按key的类型采用相应的hash算法得到key的hash值。将hash值的低位当作Hmap结构体中buckets数组的index，找到key所在的bucket。将hash的高8位存储在了bucket的tophash中。<strong style="box-sizing: border-box;">注意，这里高8位不是用来当作key/value在bucket内部的offset的，而是作为一个主键，在查找时对tophash数组的每一项进行顺序匹配的</strong>。先比较hash值高位与bucket的tophash[i]是否相等，如果相等则再比较bucket的第i个的key与所给的key是否相等。如果相等，则返回其对应的value，反之，在overflow buckets中按照上述方法继续寻找。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">整个hash的存储如下图所示(临时先采用了XX同学画的图，这个图有点问题)：</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;"><img src="https://www.maxiaoke.com/uploads/images/20231217/d3c5ab4f6f0459e5402c019694a9831d.png" alt=""/></p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">图2.2 HMap的存储结构</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">注意一个细节是Bucket中key/value的放置顺序，是将keys放在一起，values放在一起，为什么不将key和对应的value放在一起呢？如果那么做，存储结构将变成key1/value1/key2/value2… 设想如果是这样的一个map[int64]int8，考虑到字节对齐，会浪费很多存储空间。不得不说通过上述的一个小细节，可以看出Go在设计上的深思熟虑。</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>增量扩容</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">大家都知道哈希表表就是以空间换时间，访问速度是直接跟填充因子相关的，所以当哈希表太满之后就需要进行扩容。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">如果扩容前的哈希表大小为2^B，扩容之后的大小为2^(B+1)，每次扩容都变为原来大小的两倍，哈希表大小始终为2的指数倍，则有(hash mod 2^B)等价于(hash & (2^B-1))。这样可以简化运算，避免了取余操作。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">假设扩容之前容量为X，扩容之后容量为Y，对于某个哈希值hash，一般情况下(hash mod X)不等于(hash mod Y)，所以扩容之后要重新计算每一项在哈希表中的新位置。当hash表扩容之后，需要将那些旧的pair重新哈希到新的table上(源代码中称之为evacuate)，这个工作并没有在扩容之后一次性完成，而是逐步的完成（在insert和remove时每次搬移1-2个pair），Go语言使用的是增量扩容。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">为什么会增量扩容呢？主要是缩短map容器的响应时间。假如我们直接将map用作某个响应实时性要求非常高的web应用存储，如果不采用增量扩容，当map里面存储的元素很多之后，扩容时系统就会卡往，导致较长一段时间内无法响应请求。不过增量扩容本质上还是将总的扩容时间分摊到了每一次哈希操作上面。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">扩容会建立一个大小是原来2倍的新的表，将旧的bucket搬到新的表中之后，并不会将旧的bucket从oldbucket中删除，而是加上一个已删除的标记。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">正是由于这个工作是逐渐完成的，这样就会导致一部分数据在old table中，一部分在new table中，所以对于hash table的insert, remove, lookup操作的处理逻辑产生影响。只有当所有的bucket都从旧表移到新表之后，才会将oldbucket释放掉。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">扩容的填充因子是多少呢？如果grow的太频繁，会造成空间的利用率很低，如果很久才grow，会形成很多的overflow buckets，查找的效率也会下降。这个平衡点如何选取呢(在go中，这个平衡点是有一个宏控制的(#define LOAD 6.5), 它的意思是这样的，如果table中元素的个数大于table中能容纳的元素的个数，那么就触发一次grow动作。那么这个6.5是怎么得到的呢？原来这个值来源于作者的一个测试程序，遗憾的是没能找到相关的源码，不过作者给出了测试的结果：</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">        LOAD    %overflow  bytes/entry     hitprobe    missprobe        4.00         2.13        20.77         3.00         4.00        4.50         4.05        17.30         3.25         4.50        5.00         6.85        14.77         3.50         5.00        5.50        10.55        12.94         3.75         5.50        6.00        15.27        11.67         4.00         6.00        6.50        20.90        10.79         4.25         6.50        7.00        27.14        10.15         4.50         7.00        7.50        34.03         9.73         4.75         7.50        8.00        41.10         9.40         5.00         8.00 %overflow   = percentage of buckets which have an overflow bucket bytes/entry = overhead bytes used per key/value pair hitprobe    = # of entries to check when looking up a present key missprobe   = # of entries to check when looking up an absent key</pre><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">可以看出作者取了一个相对适中的值。</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>查找过程</h2><ol style="box-sizing: border-box; margin-bottom: 16px; padding: 0px 0px 0px 2em; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;" class=" list-paddingleft-2"><li><p>根据key计算出hash值。</p></li><li><p>如果存在old table, 首先在old table中查找，如果找到的bucket已经evacuated，转到步骤3。反之，返回其对应的value。</p></li><li><p>在new table中查找对应的value。</p></li></ol><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">这里一个细节需要注意一下。不认真看可能会以为低位用于定位bucket在数组的index，那么高位就是用于key/valule在bucket内部的offset。事实上高8位不是用作offset的，而是用于加快key的比较的。</p><pre class="prettyprint linenums prettyprinted" style="box-sizing: border-box; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-stretch: normal; font-size: 13.6px; line-height: 1.6; font-family: "YaHei Consolas Hybrid", Consolas, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Helvetica, monospace, monospace; margin-top: 0px; margin-bottom: 16px; overflow: auto; color: rgb(47, 111, 159); background-color: rgb(246, 246, 246); border: 1px solid rgb(238, 238, 238); padding: 10px; border-radius: 3px; overflow-wrap: break-word; text-wrap: wrap;">do { //对每个桶b    //依次比较桶内的每一项存放的tophash与所求的hash值高位是否相等    for(i = 0, k = b->data, v = k + h->keysize * BUCKETSIZE; i < BUCKETSIZE; i++, k += h->keysize, v += h->valuesize) {        if(b->tophash[i] == top) {             k2 = IK(h, k);            t->key->alg->equal(&eq, t->key->size, key, k2);            if(eq) { //相等的情况下再去做key比较...                *keyp = k2;                return IV(h, v);            }        }    }    b = b->overflow; //b设置为它的下一下溢出链} while(b != nil);</pre><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>插入过程分析</h2><ol style="box-sizing: border-box; margin-bottom: 16px; padding: 0px 0px 0px 2em; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;" class=" list-paddingleft-2"><li><p>根据key算出hash值，进而得出对应的bucket。</p></li><li><p>如果bucket在old table中，将其重新散列到new table中。</p></li><li><p>在bucket中，查找空闲的位置，如果已经存在需要插入的key，更新其对应的value。</p></li><li><p>根据table中元素的个数，判断是否grow table。</p></li><li><p>如果对应的bucket已经full，重新申请新的bucket作为overbucket。</p></li><li><p>将key/value pair插入到bucket中。</p></li></ol><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">这里也有几个细节需要注意一下。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">在扩容过程中，oldbucket是被冻结的，查找时会在oldbucket中查找，但不会在oldbucket中插入数据。如果在oldbucket是找到了相应的key，做法是将它迁移到新bucket后加入evalucated标记。并且还会额外的迁移另一个pair。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">然后就是只要在某个bucket中找到第一个空位，就会将key/value插入到这个位置。也就是位置位于bucket前面的会覆盖后面的(类似于存储系统设计中做删除时的常用的技巧之一，直接用新数据追加方式写，新版本数据覆盖老版本数据)。找到了相同的key或者找到第一个空位就可以结束遍历了。不过这也意味着做删除时必须完全的遍历bucket所有溢出链，将所有的相同key数据都删除。所以目前map的设计是为插入而优化的，删除效率会比插入低一些。</p><h2 style="box-sizing: border-box; margin-top: 0.3em; margin-bottom: 1em; font-weight: 300; line-height: 1.225; font-size: 1.75em; font-family: Raleway, 微軟正黑體, "Helvetica Neue", Helvetica, Arial, sans-serif; letter-spacing: 0.5px; position: relative; padding-bottom: 0.5em; border-bottom: 1px solid rgb(238, 238, 238); color: rgb(77, 82, 89); text-wrap: wrap;"><a class="reference-link" style="box-sizing: border-box; color: rgb(51, 202, 187); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; transition: all 0.3s linear 0s; outline: none !important;"></a>map设计中的性能优化</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">读完map源代码发现作者还是做了很多设计上的选择的。本人水平有限，谈不上优劣的点评，这里只是拿出来与读者分享。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">HMap中是Bucket的数组，而不是Bucket指针的数组。好的方面是可以一次分配较大内存，减少了分配次数，避免多次调用mallocgc。但相应的缺点，其一是可扩展哈希的算法并没有发生作用，扩容时会造成对整个数组的值拷贝(如果实现上用Bucket指针的数组就是指针拷贝了，代价小很多)。其二是首个bucket与后面产生了不一致性。这个会使删除逻辑变得复杂一点。比如删除后面的溢出链可以直接删除，而对于首个bucket，要等到evalucated完毕后，整个oldbucket删除时进行。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">没有重用设freelist重用删除的结点。作者把这个加了一个TODO的注释，不过想了一下觉得这个做的意义不大。因为一方面，bucket大小并不一致，重用比较麻烦。另一方面，下层存储已经做过内存池的实现了，所以这里不做重用也会在内存分配那一层被重用的，</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">bucket直接key/value和间接key/value优化。这个优化做得蛮好的。注意看代码会发现，如果key或value小于128字节，则它们的值是直接使用的bucket作为存储的。否则bucket中存储的是指向实际key/value数据的指针，</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">bucket存8个key/value对。查找时进行顺序比较。第一次发现高位居然不是用作offset，而是用于加快比较的。定位到bucket之后，居然是一个顺序比较的查找过程。后面仔细想了想，觉得还行。由于bucket只有8个，顺序比较下来也不算过分。仍然是O(1)只不过前面系数大一点点罢了。相当于hash到一个小范围之后，在这个小范围内顺序查找。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">插入删除的优化。前面已经提过了，插入只要找到相同的key或者第一个空位，bucket中如果存在一个以上的相同key，前面覆盖后面的(只是如果，实际上不会发生)。而删除就需要遍历完所有bucket溢出链了。这样map的设计就是为插入优化的。考虑到一般的应用场景，这个应该算是很合理的。</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(77, 82, 89); font-family: "Microsoft YaHei", Helvetica, "Meiryo UI", "Malgun Gothic", "Segoe UI", "Trebuchet MS", Monaco, monospace, Tahoma, STXihei, 华文细黑, STHeiti, "Helvetica Neue", "Droid Sans", "wenquanyi micro hei", FreeSans, Arimo, Arial, SimSun, 宋体, Heiti, 黑体, sans-serif; text-wrap: wrap;">作者还列了另个2个TODO：将多个几乎要empty的bucket合并；如果table中元素很少，考虑shrink table。(毕竟现在的实现只是单纯的grow)。</p><p><br/></p>