Shell script that keeps SSH connections open

This is somewhat like autossh but written as portable Bourne shell script, which makes life a bit easier to us poor folks who have to deal with old UNIX systems.

Keeps a SSH connection open no matter what, reconnecting when necessary. When port forwarding is requested, keepssh will make sure it is successful as well. If it's not we will drop the session and reconnect until forwarding is up, with special provisions for older OpenSSH clients that can't monitor port forwarding themselves.

This is of course mostly useful for setting up tunnels but keepssh can be used interactively too; works pretty well on a laptop when you need to move around. Close the lid, connection times out; open the lid, it is back up.

keepssh is intended to be easy to use. Run it as you would run ssh, there are no special arguments; e.g. instead of:

    ssh -o foo=yes -i ~/.ssh/identity -p 2222 [email protected]

Use this:

keepssh -o foo=yes -i ~/.ssh/identity -p 2222 [email protected]

All arguments are passed through to ssh transparently, except -f and -q; these are handled internally to produce the same behavior:

• -f will tell keepssh to drop into background; combined with KEEPSSH_PIDFILE variable (see below) this allows for easier scripting because ssh can be restarted many times and its PID will change every time but keepssh process will stay the same until terminated.

• -q will tell keepssh to be quiet. No errors or warnings are printed to stderr, just like ssh does.

There are a few extra features and behaviors controlled via env variables:

• KEEPSSH_SSH=<path> will force using SSH client at the specified path instead of the default ssh.

• KEEPSSH_VERBOSE=<level> will make keepssh log non-essential information on stderr to help with troubleshooting. Values of can be 1 or 2, with greater verbosity at 2.

• KEEPSSH_DEBUG=<level> will add debugging information to usual log messages. Level=1 will set -x and level=2 will set -xv, which is a lot of output. When debugging is requested, -q option is ignored.

• KEEPSSH_TIMEOUT=<seconds> will change the timeout between reconnect attempts (default is 5). If the time since last reconnect attempt is less than this value, the timeout is multiplied by 2 for each subsequent failed attempt, until KEEPSSH_MAX_TIMEOUT is reached. The timeout will be reset back to original KEEPSSH_TIMEOUT value after a successful connection. This is useful for preventing network flooding.

• KEEPSSH_MAX_TIMEOUT=<seconds> will change the maximum timeout betweeen reconnect attempts (default is 300).

• KEEPSSH_PIDFILE=<path> will print the PID of the process to specified file. Use this process id to stop keepssh.

• KEEPSSH_LOGFILE=<path> will divert stderr to the specified file, including ssh output on stderr. When both log file and -q option are used, keepssh will create the file but won't print anything in it.

• KEEPSSH_NO_TIMESTAMP=1 will tell keepssh not to timestamp log file messages. This variable is only meaningful when KEEPSSH_LOGFILE is used; log messages on stderr are never timestamped.

• KEEPSSH_FIFO=<path> will use the path (or mktemp pattern) to create named pipe where ssh stderr will be redirected. This is used on old systems where OpenSSH doesn't support ExitOnForwardFailure option and we have to parse its stderr for errors. Default is whatever your local mktemp command comes up with.

There are no special instructions for keepssh, it is designed to be simple and portable. Drop the script into your ~/bin and run chmod +x ~/bin/keepssh and you're all set. Something like this:

curl -L https://raw.github.com/nohuhu/keepssh/master/keepssh > ~/bin/keepssh
chmod 755 ~/bin/keepssh

Obviously you will need a SSH client to use this script. So far keepssh was tested with OpenSSH in Linux, Mac OS X and Solaris 10; there is a reasonable expectation that it might work in other systems, too.

I would very much like to make keepssh compatible with any UNIX system out there but I don't have access to anything beyond listed above. Patches and bug reports are always welcome.

Please report issues here: https://github.com/nohuhu/keepssh/issues