Quick SSH Tip | Articles - Fabien Potencier

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If you need to regularly connect to a lot of different servers like I do, you probably use SSH to connect to them, and you also probably use your personal SSH identity file to ease the connection.

Some time ago, I re-discover a neat trick to simplify the connection by using the .ssh/config file. I don't know why I forgot about it, but as it seems that a lot of people around me do not know about this file either, here is a small post on how it can be used to your advantage.

Let's say you have a host at 1.2.3.4 you need to connect to and the username you need to use is fabien. Each time you want to connect to it, you need to type something like the following:

$ ssh fabien@1.2.3.4

Simple enough, even if you need to remember the remote user you need to use for each server. However, if you need to specify a specific key, it becomes more verbose:

$ ssh -i /Users/fabien/keys/myserver.key fabien@1.2.3.4

That's difficult to remember, quite tedious to write and error prone. Instead, I want to be able to just type:

$ ssh myserver

It's quite easy. Create a .ssh/config file under your home directory and put something like this inside:

Host myserver
  HostName 1.2.3.4
  User root
  IdentityFile /Users/fabien/keys/myserver.key

That's all there is to it. Now, connecting to the server is as easy as typing:

$ ssh myserver

And it works everywhere SSH is involved. For instance, when you use scp to copy a file:

$ scp localfile.txt myserver:/tmp/

It is also a great way to not give sensitive information in configuration files. For instance, in a symfony project, the properties.ini file can contain the information to connect to the production servers used for deployment. Instead of having to hardcode the real host name, the login and the password like this:

[production]
host=www.myserver.com
port=22
user=someusername
pass=somepassword
dir=/var/www/mysite/

You can simply reference the name you gave in the config file and keep the details secret on your local machine:

[production]
host=myserver
port=22
dir=/var/www/mysite/

Unix is really powerful thanks to little things like this one. By the way, if you want to know more about the Unix history, you can read the really interesting "Unix turns 40: The past, present and future of a revolutionary OS" article published on ComputerWorld.com earlier this month.