Fundamental SSH tricks when working across multiple hosts

Time to note down some SSH tricks. Vim, Git, Unix, SSH! All very efficient when you spend some time learning the ins and outs.

Key-based login

It is hard to keep up with many hostnames and passwords so first thing to set up is a key-based login. First run ssh-keygen -t dsa and then ssh-copy-id (if not present check out this one-liner)

The power of ~/.ssh/config

Man. Check out this nice intro. Using this file is more convenient than shell aliases. I even used this file to solve a mysterious "Too many authentication failures for [user]" which happened (ssh -v) when multiple keys were offered to the remote host!

X11 forwarding

Run ssh -X host to show remote X applications on your local screen (if X is running on your local machine)

Run commands on a remote server

ssh user@remote_host 'cmd' - this is a powerful way to quickly analyze data on different hosts without the burden of logging in and copying terminal output. See a nice Perl loop example.

Pipe data from/to a remote system

One of my favorites: see this post for two powerful examples:

• 1. send a big directory to a another server compressing / uncompressing it via the pipe-to-ssh:

$ tar -cz content | ssh user@remote_host 'tar -xz'

The other way around works just as well to get files off a remote server: $ ssh remote_host tar c content/ | tar xv

• 2. backup a remote mysql database to STDOUT and receive it via pipe/SSH as STDIN to import it into a local DB:

$ ssh user@remote_host 'mysqldump -udbuser -ppassword dbname' | mysql -uroot -ppassword backup

Mount a remote directory

$ sshfs user@remote_host:/home/user/documents local_folder/ - see this ssh hacks post.

Practical example

This just happened trying to convert this post from text to html:

$ perl parsepost.pl 2013.05.12_ssh_tricks.txt 
Can't locate HTML/Entities.pm in @INC ...

Instead of fixing it right away I took the opportunity to try a quick workaround via ssh:

# cat the txt post to STDOUT,
# via pipe/ssh to remote server it goes into perl script as STDIN (-), 
# the result is redirected to a file on my local server,
# note that I can do "ssh bob" thanks to my .ssh/config setup ;)
$ cat 2013.05.12_ssh_tricks.txt | ssh bob <path>/perl/wordpress_parse_post.pl - > 2013.05.12_ssh_tricks.html

Only the beginning

Forwarding, tunneling, proxies, access to services through a firewall ... much more is possible. Check out SSH: More than secure shell for other SSH use cases.

Your favorite SSH trick/ hack?

Feel free to comment below ...