Debian/Ubuntu Tips and Tricks

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Debian/Ubuntu Tips and Tricks

How-To: Customizing SSH client

Posted by chantra on April 12th, 2008

SSH is great. There is so many thing you can do with it other than just a remote secure shell like X forwarding, port forwarding, authenticate using a private/public key, compress the transmitted stream....

If you have different account that you use on an every day basis, it becomes quickly cumbersome to type those lengthly command lines.

One could work around this by using aliases, the right way would be to use ~/.ssh/config

This tutorial will show some customization examples that should cover most ssh use cases.

All along this tutorial, the changes will be made in ~/.ssh/config and will therefore be available only for your user.
If you wish to make changes server wide, you will have to edit /etc/ssh/ssh_config .

1. A simple example

Most of your ssh connection might look like:

$ ssh user1@server1.example.com

By adding the following to your ~/.ssh/config :

Host server1
Hostname server1.example.com
User user1

You can shorten the typing to:

$ ssh server1

2. Adding Public/Private key authentication

If you identity file is named ~/.ssh/id_rsa or ~/.ssh/id_dsa , those file will be tried automatically by ssh.
In case you have different key files, you have to inform ssh about it with -i , which look like:

$ ssh -i ~/.ssh/id_rsa_server2 user2@server2.example.com

Adding the following to ~/.ssh/config :

Host server2
Hostname server2.example.com
User user2
IdentityFile ~/.ssh/id_rsa_server2

will allow you to type:

$ ssh server2

to get the same result.

3. Port Forwarding

Forwarding port with ssh requires a command line like:

$ ssh -L 8888:127.0.0.1:7777 -i .ssh/id_rsa_server3 user3@server3.example.com

The following in ~/.ssh/config :

Host server3
Hostname server3.example.com
User user3
IdentityFile ~/.ssh/id_rsa_server3
Localforward 8888 127.0.0.1:7777

will shorten the command to:

$ ssh server3

4. More options

The 3 examples above cover my needs with for my day to day use of ssh. There is plenty of other options that you might find useful.
You can find more info from :

$ man ssh_config

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