"Stupid" SSH Tricks

SSH is typically used to log into a remote machine and start up a shell session. This lets users run command line programs just as if they were sitting at a local terminal. That is a very useful ability to have in and of itself. However, some of the coolest things you can do with SSH don't involve starting an interactive session.

Here's a shortened version of the options ssh takes:

localhost$ ssh [misc. options] [user@]host [commands]

Normally, you'll see something simple along the lines of

localhost$ ssh remotehost

but, you can tack on an arbitrary command afterward to run it remotely. Let's say you need to get a list of all the users on a particular machine; there's no need to pull up a remote bash session. Just run this off:

localhost$ ssh -x remotehost 'cut -d: -f1 /etc/passwd'

    ...
    gandalf
    frodo
    ...
    localhost$

As indicated in the last line, this will leave you in your original session on the local machine. The -x option is used to turn of x forwarding; this will speed things up significantly.

Just using this method opens up a lot of options. If you have your authentication keys set up correctly, you can start running commands like this in shell scripts as well.

Also, you can poll many machines all at once. Let's say you want to check your group memberships on a bunch of machines. Use your shell's looping mechanism to do the trick.

localhost$ for box in host0{1,2,3,4}; do
  ssh -x ${box} groups
done

Nice.

Bonus stupid trick: if you want to run a remote command that requires user interaction—perhaps an ncurses application—you can have ssh request a pseudo terminal. For instance, you can open an editor on a remote file thus:

localhost$ ssh -xt vi somefile.txt

I'm sure you can come up with more interesting examples.