ssh 免手工输入密码

2018-02-02

免手工输入密码

我们可以使用 ssh 互信,sshpass 和 expect 等工具来避免手工输密码。使用过程可能会碰到如下需要手工输入 yes 的繁琐场景:

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$ ssh username@hostname
The authenticity of host ... can't be established.
ECDSA key fingerprint is ...
Are you sure you want to continue connecting (yes/no)?

为了避免出现上述场景,往 ssh 命令添加如下参数:

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$ ssh -o "StrictHostKeyChecking no" username@password

SSH 互信

SSH 互信的配置非常简单,首先生成 ssh key:

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$ ssh-keygen

把 public key 拷贝到信任方中:

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$ ssh-copy-id -i ~/.ssh/id_rsa.pub username@hostname

之后免密执行命令:

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$ ssh -o "StrictHostKeyChecking no" username@password cmd

sshpass

sshpass 是一个用于非交互的 ssh 密码验证工具,使用前先安装:

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$ yum install sshpass

使用如下:

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$ sshpass -p password ssh -o "StrictHostKeyChecking no" username@hostname cmd

expect

Expect 是用来进行自动化控制和测试的软件工具。虽然学习成本较高,但是 expect 的功能强大,利用 expect 可以方便的执行远程命令。使用前先安装:

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$ yum install expect

例如:

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#!/usr/bin/expect
 
spawn ssh -o "StrictHostKeyChecking no" username@hostname
expect "*assword*"
send "password\n"
expect "*$*"
send "command\n"
expect "*$*"
send "exit\n"
expect eof

Expect 不仅支持 ssh,还支持 scp, ftp 等工具。

支持多命令和脚本

执行多条命令

sshpass 和 expect 在支持多条命令上非常类似,只需用 && 连接命令即可:

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# ssh trust
$ ssh -o "StrictHostKeyChecking no" username@password "cmd1 && cmd2"

例如:

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# sshpass
$ sshpass -p password ssh -o "StrictHostKeyChecking no" username@password "ls -a && mkdir test"
 
# expect
......
expect "*$*"
send "ls -a && mkdir test\n"
......

执行本地脚本

对于执行本地脚本,ssh 和 sshpass 的用法类似。

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# ssh trust
$ ssh -o "StrictHostKeyChecking no" username@password bash -s < shell_script.sh
 
# sshpass
$ sshpass -p password ssh -o "StrictHostKeyChecking no" username@password bash -s < shell_script.sh

对于 expect,首先需要把脚本拷贝到远程主机,然后在远程主机执行该脚本,步骤如下:

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...
# Copy script to remote host
spawn scp -o "StrictHostKeyChecking no" shell_script.sh username@hostname:~/
expect "*assword*"
send "password\n"
expect "*100%*"
expect eof
 
# Execute the shell script at remote host
spawn ssh -o "StrictHostKeyChecking no" username@hostname
expect "*assword*"
send "password\n"
expect "*$*"
send "sh shell_script.sh\n"
......

支持执行 sudo 命令

有些命令需要 sudo 权限才能执行,但是我们不希望重复的输入密码,我们可以把每条命令修改为如下:

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cmd ---> 'echo password | sudo -S cmd'

例如:

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sshpass -p password ssh -o "StrictHostKeyChecking no" username@password "echo password | sudo -S mkdir /newdir"

对于如 echo, dd 等部分命令,有时会出现如下失败场景:

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$ sshpass -p password ssh -o "StrictHostKeyChecking no" username@password 'echo password | sudo -S echo hello > /newdir/newfile'
bash: /newdir/newfile: 权限不够

解决办法如下:

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cmd ---> 'echo password | sudo -S sh -c "cmd"'
 
# For example
$ sshpass -p password ssh -o "StrictHostKeyChecking no" username@password 'echo WSfdl097018= | sudo -S sh -c "echo hello >  /newdir/newfile"'

如果采用 expect,需要把脚本拷贝到远程主机,然后在远程主机采用 sudo 执行该脚本,相对 sshpass 更简便和健壮:

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...
# Copy script to remote host
spawn scp -o "StrictHostKeyChecking no" shell_script.sh username@hostname:~/
expect "*assword*"
send "password\n"
expect "*100%*"
expect eof
 
# Execute the shell script at remote host
spawn ssh -o "StrictHostKeyChecking no" username@hostname
expect "*assword*"
send "password\n"
expect "*$*"
send "sudo sh shell_script.sh\n"
expect "*assword*"
send "password\n"
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