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Linux运维-从vim编辑器开始
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LInux运维零基础入门到实战
小册名称：LInux运维零基础入门到实战
你可能已经知道，[SSH](https://en.wikipedia.org/wiki/Secure_Shell) 是一种网络协议，允许你通过网络登录到`vm1`。让我们详细研究一下。 > 安全 Shell（SSH）是一种网络协议，用于安全数据通信，远程 Shell 服务或命令执行，以及其它两个联网计算机之间的网络服务，它们通过不安全网络上的安全通道连接：服务器和客户端（运行 SSH 服务器和 SSH 客户端程序）。协议规范区分了两个主要版本，被称为 SSH-1 和 SSH-2。 > 协议最著名的应用是，访问类 Unix 操作系统上的 shell 帐户。它为替代 Telnet 和其他不安全的远程 shell 协议而设计，如 Berkeley rsh 和 rexec 协议，它们以明文形式发送信息，特别是密码，使得它们易于使用封包分析来拦截和暴露。SSH 使用的加密 旨在通过不安全的网络（如互联网）提供数据的机密性和完整性。 重要的 SSH 程序，概念和配置文件： + [OpenSSH](https://en.wikipedia.org/wiki/OpenSSH) - 开源的 ssh 程序实现。 + `ssh` - 允许你连接到 SSH 服务器的客户端程序。Putty 就是这样的客户端程序。 + `sshd` - 服务器程序，允许你使用`ssh`连接到它。 + `/etc/ssh/ssh_config` - 默认的客户端程序配置文件。 + `/etc/ssh/sshd_config` - 默认服务器程序配置文件。 + [公钥密码系统](https://en.wikipedia.org/wiki/Public-key_cryptography) - 一种需要两个单独密钥的加密系统，其中一个密钥是私钥，其中一个密钥是公钥。虽然不同，密钥对的两个部分在数学上是相关的。一旦密钥锁定或加密了明文，另一个密钥解锁或解密密文。两个密钥都不能执行这两个功能。其中一个密钥是公开发布的，另一个密钥是保密的。 + SSH 密钥 - SSH 使用公钥密码系统来认证远程计算机，并允许它对用户进行认证（如有必要）。任何人都可以生成一对匹配的不同密钥（公钥和私钥）。公钥放置在所有计算机上，它们允许访问匹配的私钥的所有者（所有者使私钥保密）。虽然认证基于私钥，但认证期间密钥本身不会通过网络传输。 + `/etc/ssh/moduli` - 质数及其生成器，由`sshd(8)`用于 Diffie-Hellman Group Exchange 密钥交换方法中。 + `/etc/ssh/ssh_host_dsa_key`, `/etc/ssh/ssh_host_rsa_key` - 主机 RSA 和 DSA 私钥。 + `/etc/ssh/ssh_host_dsa_key.pub`, `/etc/ssh/ssh_host_rsa_key.pub` - 主机 RSA 和 DSA 公钥。 SSH 协议非常重要，因此被广泛使用，并且具有如此多的功能，你必须了解它的一些工作原理。这是它的一些用途： + `scp` - 通过 SSH 传输文件。 + `sftp` - 类似 ftp 的协议，用于管理远程文件。 + `sshfs` - SSH 上的远程文件系统。 + SSH 隧道 - 一种通过安全连接，传输几乎任何数据的方法。这是非常重要的，因为它可以用于构建受保护系统的基础，以及许多其他用途。 为了了解这个协议，让我们看看，在 SSH 会话中会发生了什么。为此，我们将开始研究`vm1`到`vm1`的连接的带注解的输出（是的，这是可以做到的，也是完全有效的）。概述： ``` 你 输入 SSH VM1 控制权现在传递给 SSH 客户端 SSH 客户端 进入明文阶段 读取配置 与 SSH 服务器进行协议协商 进入 SSH 传输阶段 与 SSH 服务器进行协商 数据加密密码 数据完整性算法 数据压缩算法 使用 Diffie-Hellman 算法启动密钥交换 所得共享密钥用于建立安全连接 进入 SSH-userauth 阶段 要求你输入密码 控制权现在传递给你 你 输入密码 控制权现在传递给 SSH 客户端 SSH 客户端 在 SSH 服务器对你进行认证 进入 SSH 连接阶段 为你分配伪终端 为你启动 shell 控制权现在传递给你 你 在 vm1 上做一些（没）有用的事情 关闭 shell 控制全现在传递给 SSH 客户端 SSH 客户端 关闭伪终端 关闭连接 ``` 现在阅读这个： + [SSH 协议揭秘](https://www.linuxjournal.com/article/9566) + <http://www.cs.ust.hk/faculty/cding/COMP581/SLIDES/slide24.pdf> 并研究 SSH 会话的真实输出： ``` user1@vm1:~$ ssh -vv vm1 Protocol version selection, plaintext ------------------------------------- OpenSSH_5.5p1 Debian-6+squeeze2, OpenSSL 0.9.8o 01 Jun 2010 # Speaks for itself, I will mark such entries with -- below debug1: Reading configuration data /etc/ssh/ssh_config # Applying default options for all hosts. Additional options for each host may be # specified in the configuration file debug1: Applying options for * debug2: ssh_connect: needpriv 0 debug1: Connecting to vm1 [127.0.1.1] port 22. debug1: Connection established. debug1: identity file /home/user1/.ssh/id_rsa type -1 # no such files debug1: identity file /home/user1/.ssh/id_rsa-cert type -1 debug1: identity file /home/user1/.ssh/id_dsa type -1 debug1: identity file /home/user1/.ssh/id_dsa-cert type -1 debug1: Remote protocol version 2.0, remote software version OpenSSH_5.5p1 Debian-6+squeeze2 debug1: match: OpenSSH_5.5p1 Debian-6+squeeze2 pat OpenSSH* debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_5.5p1 Debian-6+squeeze2 debug2: fd 3 setting O_NONBLOCK SSH-transport, binary packet protocol ------------------------------------- debug1: SSH2_MSG_KEXINIT sent debug1: SSH2_MSG_KEXINIT received # Key exchange algorithms debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 # SSH host key types debug2: kex_parse_kexinit: ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,ssh-rsa,ssh-dss # Data encryption ciphers debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se # Data integrity algorithms debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 # Data compression algorithms debug2: kex_parse_kexinit: none,zlib@openssh.com,zlib debug2: kex_parse_kexinit: none,zlib@openssh.com,zlib debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: first_kex_follows debug2: kex_parse_kexinit: reserved 0 # Messages back from server debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 debug2: kex_parse_kexinit: ssh-rsa,ssh-dss debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: none,zlib@openssh.com debug2: kex_parse_kexinit: none,zlib@openssh.com debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: first_kex_follows 0 debug2: kex_parse_kexinit: reserved 0 # Message authentication code setup debug2: mac_setup: found hmac-md5 debug1: kex: server->client aes128-ctr hmac-md5 none debug2: mac_setup: found hmac-md5 debug1: kex: client->server aes128-ctr hmac-md5 none # Key exchange debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP debug2: dh_gen_key: priv key bits set: 135/256 debug2: bits set: 498/1024 debug1: SSH2_MSG_KEX_DH_GEX_INIT sent debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY # Server authentication. vm1 host key is not known because it is our first connection debug2: no key of type 0 for host vm1 debug2: no key of type 2 for host vm1 # Confirmation of host key acceptance The authenticity of host 'vm1 '(127.0.1.1)' can't be established. RSA key fingerprint is b6:06:92:5e:04:49:d9:e8:57:90:61:1b:16:87:bb:09. Are you sure you want to continue connecting (yes/no)? yes Warning: Permanently added 'vm1' (RSA) to the list of known hosts. # Key is added to /home/user1/.ssh/known_hosts and checked debug2: bits set: 499/1024 debug1: ssh_rsa_verify: signature correct # Based on shared master key, data encryption key and data integrity key are derived debug2: kex_derive_keys debug2: set_newkeys: mode 1 # Information about this is sent to server debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug2: set_newkeys: mode 0 debug1: SSH2_MSG_NEWKEYS received # IP roaming not enabled? Not sure about this. debug1: Roaming not allowed by server SSH-userauth ------------ debug1: SSH2_MSG_SERVICE_REQUEST sent debug2: service_accept: ssh-userauth debug1: SSH2_MSG_SERVICE_ACCEPT received debug2: key: /home/user1/.ssh/id_rsa ((nil)) debug2: key: /home/user1/.ssh/id_dsa ((nil)) debug1: Authentications that can continue: publickey,password debug1: Next authentication method: publickey debug1: Trying private key: /home/user1/.ssh/id_rsa debug1: Trying private key: /home/user1/.ssh/id_dsa debug2: we did not send a packet, disable method debug1: Next authentication method: password user1@vm1''s password: debug2: we sent a password packet, wait for reply debug1: Authentication succeeded (password). SSH-connection -------------- debug1: channel 0: new [client-session] debug2: channel 0: send open # Disable SSH mutiplexing. # More info: http://www.linuxjournal.com/content/speed-multiple-ssh-connections-same-server debug1: Requesting no-more-sessions@openssh.com debug1: Entering interactive session. debug2: callback start debug2: client_session2_setup: id 0 debug2: channel 0: request pty-req confirm 1 # Sending environment variables debug1: Sending environment. debug1: Sending env LANG = en_US.UTF-8 debug2: channel 0: request env confirm 0 debug2: channel 0: request shell confirm 1 # Set TCP_NODELAY flag: http://en.wikipedia.org/wiki/Nagle%27s_algorithm debug2: fd 3 setting TCP_NODELAY debug2: callback done # Connection opened debug2: channel 0: open confirm rwindow 0 rmax 32768 debug2: channel_input_status_confirm: type 99 id 0 # Pseudo terminal allocation debug2: PTY allocation request accepted on channel 0 debug2: channel 0: rcvd adjust 2097152 debug2: channel_input_status_confirm: type 99 id 0 # Shell is started debug2: shell request accepted on channel 0 # Loggin in is completed Linux vm1 2.6.32-5-amd64 #1 SMP Sun May 6 04:00:17 UTC 2012 x86_64 The programs included with the Debian GNU/Linux system are free software; the exact distribution terms for each program are described in the individual files in /usr/share/doc/*/copyright. Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law. You have mail. Last login: Thu Jul 19 05:14:40 2012 from 10.0.2.2 user1@vm1:~$ debug2: client_check_window_change: changed debug2: channel 0: request window-change confirm 0 user1@vm1:~$ debug2: client_check_window_change: changed debug2: channel 0: request window-change confirm 0 user1@vm1:~$ logout Ending ssh connection --------------------- debug2: channel 0: rcvd eof # end of file debug2: channel 0: output open -> drain debug2: channel 0: obuf empty debug2: channel 0: close_write debug2: channel 0: output drain -> closed debug1: client_input_channel_req: channel 0 rtype exit-status reply 0 # signalling that channels are half-closed for writing, through a channel protocol extension # notification "eow@openssh.com" http://www.openssh.com/txt/release-5.1 debug1: client_input_channel_req: channel 0 rtype eow@openssh.com reply 0 debug2: channel 0: rcvd eow # Ending connection debug2: channel 0: close_read debug2: channel 0: input open -> closed debug2: channel 0: rcvd close debug2: channel 0: almost dead debug2: channel 0: gc: notify user debug2: channel 0: gc: user detached debug2: channel 0: send close debug2: channel 0: is dead debug2: channel 0: garbage collecting debug1: channel 0: free: client-session, nchannels 1 Connection to vm1 closed. Transferred: sent 1928, received 2632 bytes, in 93.2 seconds Bytes per second: sent 20.7, received 28.2 debug1: Exit status 0 user1@vm1:~$ ``` 现在，你将学习如何在调试模式下启动`sshd`，使用`scp`建立公钥认证和复制文件。 ## 这样做 ``` 1: mkdir -v ssh_test 2: cd ssh_test 3: cp -v /etc/ssh/sshd_config . 4: sed -i'.bak' 's/^Port 22$/Port 1024/' sshd_config 5: sed -i 's/^HostKey \/etc\/ssh\/ssh_host_rsa_key$/Hostkey \/home\/user1\/ssh_test\/ssh_host_rsa_key/' sshd_config 6: sed -i 's/^HostKey \/etc\/ssh\/ssh_host_dsa_key$/Hostkey \/home\/user1\/ssh_test\/ssh_host_dsa_key/' sshd_config 7: diff sshd_config.bak sshd_config 8: ssh-keygen -b 4096 -t rsa -N '' -v -h -f ssh_host_rsa_key 9: ssh-keygen -b 1024 -t dsa -N '' -v -h -f ssh_host_dsa_key 10: ssh-keygen -b 4096 -t rsa -N '' -v -f ~/.ssh/id_rsa 11: cat ~/.ssh/id_rsa.pub > ~/.ssh/authorized_keys 12: /usr/sbin/sshd -Ddf sshd_config > sshd.out 2>&1 & 13: ssh-keyscan -H vm1 127.0.0.1 >> ~/.ssh/known_hosts 14: /usr/sbin/sshd -Ddf sshd_config >> sshd.out 2>&1 & 15: ssh vm1 -v -p 1024 2>ssh.out 16: ps au --forest 17: logout 18: /usr/sbin/sshd -Ddf sshd_config >> sshd.out 2>&1 & 19: scp -v -P 1024 vm1:.bashrc . 2>scp.out ``` ## 你会看到什么 ``` user1@vm1:~$ mkdir -v ssh_test mkdir: created directory 'ssh_test' user1@vm1:~$ cd ssh_test user1@vm1:~/ssh_test$ cp -v /etc/ssh/sshd_config . '/etc/ssh/sshd_config' -> './sshd_config' user1@vm1:~/ssh_test$ sed -i'.bak' 's/^Port 22$/Port 1024/' sshd_config user1@vm1:~/ssh_test$ sed -i 's/^HostKey \/etc\/ssh\/ssh_host_rsa_key$/Hostkey \/home\/user1\/ssh_test\/ssh_host_rsa_key/' sshd_config user1@vm1:~/ssh_test$ sed -i 's/^HostKey \/etc\/ssh\/ssh_host_dsa_key$/Hostkey \/home\/user1\/ssh_test\/ssh_host_dsa_key/' sshd_config user1@vm1:~/ssh_test$ diff sshd_config.bak sshd_config 5c5 < Port 22 --- > Port 1024 11,12c11,12 < HostKey /etc/ssh/ssh_host_rsa_key < HostKey /etc/ssh/ssh_host_dsa_key --- > Hostkey /home/user1/ssh_test/ssh_host_rsa_key > Hostkey /home/user1/ssh_test/ssh_host_dsa_key user1@vm1:~/ssh_test$ ssh-keygen -b 4096 -t rsa -N '' -v -h -f ssh_host_rsa_key Generating public/private rsa key pair. Your identification has been saved in ssh_host_rsa_key. Your public key has been saved in ssh_host_rsa_key.pub. The key fingerprint is: 8c:0a:8d:ae:c7:34:e6:29:9c:c2:14:29:b8:d9:1d:34 user1@vm1 'The key's randomart image is: +--[ RSA 4096]----+ | | | E | |. .. . | |oo o. o | |.++.... S | |oo=... | |+=oo. | |o== | |oo | +-----------------+ user1@vm1:~/ssh_test$ ssh-keygen -b 1024 -t dsa -N '' -v -h -f ssh_host_dsa_key Generating public/private dsa key pair. Your identification has been saved in ssh_host_dsa_key. Your public key has been saved in ssh_host_dsa_key.pub. The key fingerprint is: cd:6b:2a:a2:ba:80:65:71:85:ef:2e:6a:c0:a7:d9:aa user1@vm1 'The key's randomart image is: +--[ DSA 1024]----+ | .. | | .. | | . .. | | o . o | |. o . S o | |o+ . . . | |o.= . o | |.o..o o o | |E=+o o .. | +-----------------+ user1@vm1:~/ssh_test$ ssh-keygen -b 4096 -t rsa -N '' -v -f ~/.ssh/id_rsa Generating public/private rsa key pair. Your identification has been saved in /home/user1/.ssh/id_rsa. Your public key has been saved in /home/user1/.ssh/id_rsa.pub. The key fingerprint is: 50:65:18:61:3f:41:36:07:4f:40:36:a7:4b:6d:64:28 user1@vm1 'The key's randomart image is: +--[ RSA 4096]----+ | =B&+* | | oE=.& | | . .= + | | . . + | | S . | | | | | | | | | +-----------------+ user1@vm1:~/ssh_test$ cat ~/.ssh/id_rsa.pub > ~/.ssh/authorized_keys user1@vm1:~/ssh_test$ /usr/sbin/sshd -Ddf sshd_config > sshd.out 2>&1 & [2] 26896 user1@vm1:~/ssh_test$ ssh-keyscan -H vm1 127.0.0.1 >> ~/.ssh/known_hosts # 127.0.0.1 SSH-2.0-OpenSSH_5.5p1 Debian-6+squeeze2 # vm1 SSH-2.0-OpenSSH_5.5p1 Debian-6+squeeze2 [2]+ Exit 255 /usr/sbin/sshd -Ddf sshd_config > sshd.out 2>&1 user1@vm1:~/ssh_test$ /usr/sbin/sshd -Ddf sshd_config >> sshd.out 2>&1 & [1] 26957 user1@vm1:~/ssh_test$ ssh vm1 -v -p 1024 2>ssh.out Linux vm1 2.6.32-5-amd64 #1 SMP Sun May 6 04:00:17 UTC 2012 x86_64 The programs included with the Debian GNU/Linux system are free software; the exact distribution terms for each program are described in the individual files in /usr/share/doc/*/copyright. Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law. You have mail. Last login: Fri Jul 20 09:10:30 2012 from vm1.site Environment: LANG=en_US.UTF-8 USER=user1 LOGNAME=user1 HOME=/home/user1 PATH=/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games MAIL=/var/mail/user1 SHELL=/bin/bash SSH_CLIENT=127.0.1.1 47456 1024 SSH_CONNECTION=127.0.1.1 47456 127.0.1.1 1024 SSH_TTY=/dev/pts/0 TERM=xterm user1@vm1:~$ ps au --forest USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND user1 26224 0.0 1.2 23660 6576 pts/2 Ss 09:09 0:01 -bash user1 27020 1.0 0.6 68392 3236 pts/2 S 09:50 0:00 \_ sshd: user1 [priv] user1 27025 0.0 0.2 68392 1412 pts/2 S 09:50 0:00 | \_ sshd: user1@pts/0 user1 27026 9.0 1.2 23564 6404 pts/0 Ss 09:50 0:00 | \_ -bash user1 27051 0.0 0.2 16308 1060 pts/0 R+ 09:50 0:00 | \_ ps au --forest user1 27021 1.1 0.5 38504 2880 pts/2 S+ 09:50 0:00 \_ ssh vm1 -v -p 1024 root 1107 0.0 0.1 5932 620 tty6 Ss+ Jul18 0:00 /sbin/getty 38400 tty6 root 1106 0.0 0.1 5932 616 tty5 Ss+ Jul18 0:00 /sbin/getty 38400 tty5 root 1105 0.0 0.1 5932 620 tty4 Ss+ Jul18 0:00 /sbin/getty 38400 tty4 root 1104 0.0 0.1 5932 620 tty3 Ss+ Jul18 0:00 /sbin/getty 38400 tty3 root 1103 0.0 0.1 5932 616 tty2 Ss+ Jul18 0:00 /sbin/getty 38400 tty2 root 1102 0.0 0.1 5932 616 tty1 Ss+ Jul18 0:00 /sbin/getty 38400 tty1 user1@vm1:~$ logout user1@vm1:~/ssh_test$ [1]+ Exit 255 /usr/sbin/sshd -Ddf sshd_config > sshd.out 2>&1 user1@vm1:~/ssh_test$ /usr/sbin/sshd -Ddf sshd_config >> sshd.out 2>&1 & [1] 27067 user1@vm1:~/ssh_test$ scp -v -P 1024 vm1:.bashrc . 2>scp.out Environment: LANG=en_US.UTF-8 USER=user1 LOGNAME=user1 HOME=/home/user1 PATH=/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games MAIL=/var/mail/user1 SHELL=/bin/bash SSH_CLIENT=127.0.1.1 47459 1024 SSH_CONNECTION=127.0.1.1 47459 127.0.1.1 1024 .bashrc 100% 3184 3.1KB/s 00:00 [1]+ Exit 255 /usr/sbin/sshd -Ddf sshd_config >> sshd.out 2>&1 ``` ## 解释 1. 创建`/home/user1/ssh_test`目录。 1. 使其成为当前工作目录。 1. 将`sshd_config`复制到此目录。 1. 将`sshd`监听端口从 22 更改为 1024，将副本命名为`sshd_config.bak`。 1. 替换 RSA 主机密钥位置。 1. 替换 DSA 主机密钥位置。 1. 显示`sshd_config`的旧版本和新版本之间的差异。 1. 生成具有空密码的，新的 4096 位 RSA 主机密钥对，将其保存到`/home/user1/ssh_test/ssh_host_rsa_key`和`/home/user1/ssh_test/ssh_host_rsa_key.pub`。 1. 同样的，但是对 DSA 密钥执行。 1. 生成新的认证密钥对，将其保存到`/home/user1/.ssh/id_rsa`和`/home/user1/.ssh/id_rsa.pub`。 1. 将`id_rsa.pub`复制到`/home/user1/.ssh/authorized_keys`，来允许无密码认证。 1. 在调试模式下，在端口 1024 上启动新的 SSH 服务器，将所有输出保存到`sshd.log`。 1. 提取 SSH 客户端的主机认证密钥，并将其提供给`/home/user1/.ssh/known_hosts`。 1. 在调试模式下，在端口 1024 上启动新的 SSH 服务器，将所有输出附加到`sshd.log`。这是因为在调试模式下， SSH 服务器只维护一个连接。 1. 使用`ssh`客户端连接到此服务器。 1. 以树形式打印当前正在运行的进程。你可以看到，你正在使用`sshd`启动的 bash，它服务于你的连接，而`sshd`又是由`sshd`启动，你在几行之前启动了你自己。。 1. 退出`ssh`会话。 1. 再次启动 SSH 服务器。 1. 将文件`.bashrc`从你的主目录复制到当前目录。 ## 附加题 观看此视频，它解释了加密如何工作：<http://www.youtube.com/watch?v=3QnD2c4Xovk> 阅读：<http://docstore.mik.ua/orelly/networking_2ndEd/ssh/ch03_04.htm> 阅读文件`ssh.out`，`scp.out`和`sshd.out`中的调试输出。向你自己解释发生了什么。
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