autossh - Automatically restart SSH sessions and tunnels
Update: Version 1.4e always sets the first poll time equal to the poll time, unless the first poll time is explicitly set with AUTOSSH_FIRST_POLL.
Previous update: version 1.4d fixes file descriptor issues when started without standard input available (for example, in system initialization scripts).
Previous update: version 1.4c disables the "gatetime" behaviour when -f is used, updates the list of OpenSSH options it knows about, and adds some fixes to configure.
Previous update: version 1.4b fixed a bug in polling, added a max lifetime option and a compile-time option to touch the pid file on each connection test.
FEATURES
- autossh is a program to start a copy of ssh and monitor it, restarting it as necessary should it die or stop passing traffic. The idea is from rstunnel (Reliable SSH Tunnel), but implemented in C.
- The author's view is that it is not as fiddly as rstunnel to get to work.
- Connection monitoring using a loop of port forwardings or a remote echo service.
- Backs off on rate of connection attempts when experiencing rapid failures such as connection refused.
- Compiled and tested on OpenBSD, Linux, Solaris, Mac OS X, Cygwin, and AIX; should work on other BSDs.
- Freeware.
FUN
- Use with "screen" for perpetual session (see included script "rscreen").
DEFICIENCIES
- Bugs still not found.
BUILD
If you use OpenBSD or FreeBSD, autossh is available in the ports tree, and as a package that can be FTP'd down. Cygwin and some Linux distros also have it available as a package.
To build from source:
- download autossh-1.4e.tgz (md5/sha1/sha256)
- gunzip -c autossh-1.4e.tgz | tar xvf -
- cd autossh-1.4e
- ./configure
- make
- copy binary to where you wish it, or "make install" will install it under /usr/local by default.
- examine autossh.host for example wrapper script and options
USE
- Read README for documentation.
- Or once installed, read the man page.
from http://www.harding.motd.ca/autossh/
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Build a wheel of autossh using expect
题目的意思是，用expect给autossh再造一个轮子。为什么又要造轮子呢？我们先从autossh说起。
autossh是个很方便的管理ssh连接的工具。但是出于安全性的考虑，ssh连接一段时间后没有活动，就会自动断开。对于我们这些把ssh主要用做穿墙代理工具的同学，无疑是很不方便的。所以很多人都使用autossh这个工具。autossh会运行一个ssh子进程，并每隔一段时间检测ssh连接的状态，当ssh进程意外退出或连接断开时，autossh会重启ssh进程。如果你的ssh服务器使用的是密钥认证的方式，autossh可以很完美的工作。但问题来了，如果你不得不使用密码认证的方式呢？当你用autossh登陆ssh服务器，输入密码，连接建立了，可以穿墙了！过了一会儿，ssh连接超时，自动断开。autossh也意识到了这一点，于是它重启了一个ssh进程，连接上服务器，接下来 - 输入密码… autossh可是不会帮你再输入密码的。所以，在密码认证的情况下，autossh基本算是废了。这也就是我们要再造一个autossh的轮子的原因，而且要比它更圆，能自动输入密码。
我的方案是使用expect这个工具。expect可以读取程序的输出，分析输出的内容，与期望的输出进行对比，并模拟输入。如果你玩什么基于文本的MUD游戏，就可以用它来来自动完成枯燥的练级过程。我们首先很自然的就想到，用expect脚本来给autossh输入密码。在我们的这个情景中，我们希望autossh作为expect脚本的子进程，当脚本结束时，autossh也跟着结束。否则再次运行expect脚本，由于autossh还在后台，就会出现错误，除非你手动结束它。但是经过实践，发现autossh有一个问题，当autossh的父进程被结束时，其自身并不会跟着结束，而是变成孤儿进程，被init收养（Mac OS下是launchd）。这在应用中就比较麻烦了。所以我们跳过autossh，直接用expect来控制ssh，实现autossh的功能，也就是给autossh再造一个轮子。
实现的expect脚本如下，或直接点击下载：
!/usr/bin/expect --
!/bin/sh
autossh.sh
SimpleSSHProxy
Created by ivan on 10-9-10.
http://twitter.com/ivan_wl
This is another wheel of autossh built using expect.
If you have to use ssh password authorizing,
use this instead of autossh.
WARNING: This script is NOT SAFE for your password,
DON'T USE THIS IF YOU HAVE SECURITY CONCERNS!
Usage: autossh.sh [foo] [foo] [bindingIP:port] [foo] [username]
[remoteHost] [password]
get arguments
set IPandPort [lrange $argv 2 2]
set username [lrange $argv 4 4]
set remoteHost [lrange $argv 5 5]
set password [lrange $argv 6 6]
set username [lrange $argv 4 4]
set remoteHost [lrange $argv 5 5]
set password [lrange $argv 6 6]
while (1) {
set connectedFlag 0;
spawn /usr/bin/ssh -D $IPandPort $username@$remoteHost;
match_max 100000;
set timeout 60;
expect {
"?sh: Error"
{ puts "CONNECTION_ERROR"; exit; }
"yes/no"
{ send "yes\r"; exp_continue; }
"?assword:" {
send "$password\r"; set timeout 4;
expect "?assword:*" { puts "WRONG_PASSWORD"; exit; }
set connectedFlag 1;
}
set connectedFlag 0;
spawn /usr/bin/ssh -D $IPandPort $username@$remoteHost;
match_max 100000;
set timeout 60;
expect {
"?sh: Error"
{ puts "CONNECTION_ERROR"; exit; }
"yes/no"
{ send "yes\r"; exp_continue; }
"?assword:" {
send "$password\r"; set timeout 4;
expect "?assword:*" { puts "WRONG_PASSWORD"; exit; }
set connectedFlag 1;
}
if no password
"~"
{ send "echo hello\r"; set connectedFlag 1; }
}
if { $connectedFlag == 0 } {
close;
puts "SSH server unavailable, retrying...";
continue;
}
{ send "echo hello\r"; set connectedFlag 1; }
}
if { $connectedFlag == 0 } {
close;
puts "SSH server unavailable, retrying...";
continue;
}
while (1) {
set conAliveFlag 0;
interact {
set conAliveFlag 0;
interact {
time interval for checking connection
timeout 60 {
set timeout 10;
send "echo hello\r";
expect "hello" { set conAliveFlag 1; }
if { $conAliveFlag == 1 } {
set timeout 10;
send "echo hello\r";
expect "hello" { set conAliveFlag 1; }
if { $conAliveFlag == 1 } {
connection is alive
continue;
} else { break; }
}
}
}
} else { break; }
}
}
}
close;
puts "SSH connection failed, restarting...";
}
puts "SSH connection failed, restarting...";
}
将上面的代码保存为一个文本文件，如autossh.sh，chmod加上x属性，使用方法为：
autossh.sh [foo] [foo] [bindingIP:port] [foo] [username] [remoteHost] [password]
其中的 foo 参数并无实际意义，可以用任何字符串代替，保留其的目的是使此脚本与autossh的参数调用方法兼容。
这个脚本可以自动输入ssh密码，并且实现autossh的主要功能，即ssh连接的断线检测和重连，但是无法实现ssh进程意外退出时重生ssh进程。当ssh进程意外退出（比如你手动杀掉）脚本进程也就退出了。不过这种情况实在比较难以遇到，所以也算是合格。如果实在需要ssh进程的重生，可以考虑这么一种思路：再用一层expect脚本来包裹这个脚本进程，在外层脚本中实现进程的重生功能，（这个用while循环和wait命令是非常容易实现的）这个问题就留给有心的读者自己研究吧。
from https://linuxtoy.org/archives/build-a-wheel-of-autossh-using-expect.html
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AutoSSH
AutoSSH 的使用方法和 SSH 类似，只是它提供了断线自动连接功能，这样就不必每次重新输入命令了。
安装
sudo apt-get install autossh
使用
autossh -M 2000 username@hostip -p ssh_port_no -D 7070
