When doing an audit of an existing Linux server a good first step is to find out what distribution is running and if the server is running a 32 or 64 bit architecture.
To find out what architecture a server is running you can run the uname command, which will print out certain system information. This must be supplied with the -a flag in order to print out as much information as possible.
This will print out a line similar to the following on an Ubuntu system.
Linux vlad 3.2.0-23-generic #36-Ubuntu SMP Tue Apr 10 20:39:51 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
This can be broken down bit by bit and will contain the following information.