SSH Tricks: Working With a Config

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Eric Hansen

Guest
SSH is pretty much the go-to method of remotely logging into a machine in terms of Linux. Its so vital that it often comes installed by default for server-intended OSes. Its even used for code versioning systems (CVS) such as Git to do a bulk of what its use is for.

What happens, however, when you have too many hosts that you need to connect to, or even have too many connections to make on one host (using different credentials)? Well, you can either do it the old fashioned long-hand way, or use a custom SSH config file!

Here's a real life scenario I experience daily that will give you some idea as to how effective this can be. There's 5 servers I need to manage at any given point. On top of that, I have 3 different CVS accounts that I need to use as well (2 for GitHub and 1 for BitBucket). That means I have 8 different SSH profiles I need to manage. Even with using keyfiles for authentication it gets annoying having to type "ssh [email protected]" or "scp some.tar.gz [email protected]:." Being able to connect via "ssh server1" or "scp some.tar.gz server1:." is a lot easier, no?

What File To Edit?
You need to edit the ~/.ssh/config file. If it doesn't already exist that's fine (typically isn't unless you've done this already).

Where To Start?
Lets take my server1.example.tld as a sample here. We'll want to be able to reference this host by the name of "server1" and use the keyfile ~/.ssh/server1 for authentication and log in as "ehansen". Here's what we need to have:
Code:
Host server1
    HostName server1.example.tld
    IdentityFile /home/ehansen/.ssh/server1
    User ehansen

If "Host" would be "server1.example.tld" or we added an entry to our resolv.conf file to point server1 to a specific location, then we wouldn't have to add the HostName field, but that's not the point of this article. :)

HostName is the FQDN of the server we want to connect to. IdentityFile is the keyfile (via ssh-keygen) that we want to use for authentication. The "User" option isn't necessary if you're already logged in on your machine as that user, but its always nice to specify regardless.

Now, instead of having to even type "ssh server1.example.tld" we can just type "ssh server1". SSH will then parse the config file and see we're wanting the Host server1 and use the settings made from there.

You can do this for as many hosts as you want, and if you're curious what other options you can set just read the man page for ssh_config (5) and it will give you all the information you need.
 

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OP
C

CesarCara

Guest
If I can only access my server by IP?
Would it be like this?

Code:
Host server1
    HostName 192.168.x.x
    IdentityFile /home/ehansen/.ssh/server1
    User ehansen
 
OP
E

Eric Hansen

Guest
If I can only access my server by IP?
Would it be like this?

Code:
Host server1
    HostName 192.168.x.x
    IdentityFile /home/ehansen/.ssh/server1
    User ehansen
Yeaup! Of course changing the IdentityFile and User of the server information, but overall that'd be correct. ;)
 
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