From LQWiki

This page lists methods to determine which distribution a system belongs to. It is a pity but every distribution has its own way to find out what distribution you are using. So you have to try all of the below methods till you find a positive match:

• SUSE

Open a console and enter:

[ -e /etc/SuSE-release ] && echo This is a SuSE system.

• Red Hat

Open a console and enter:

[ -e /etc/redhat-release ] && echo This is a redhat system.

• Fedora

Open a console and enter:

[ -e /etc/fedora-release ] && echo This is a fedora system.

• Debian

Open a console and enter:

[ -e /etc/debian-version ] && echo This is a debian or ubuntu system.

• Slackware

Open a console and enter:

[ -e /etc/slackware-version ] && echo This is a slackware system.

• Ubuntu

Open a console and enter:

lsb_release -rd

Kernel version information

To find out your kernel version, use the command

uname -a

To find out additional info about the C compiler that built the kernel, use

cat /proc/version