When supporting systems you have inherited or in environments that have many different OS versions and distributions of Linux. There are times when you simply don't know off hand what OS version or distribution the server you are logged into is.
Luckily there is a simple way to figure that out.
$ cat /etc/lsb-release DISTRIB_ID=Ubuntu DISTRIB_RELEASE=13.04 DISTRIB_CODENAME=raring DISTRIB_DESCRIPTION="Ubuntu 13.04"
# cat /etc/redhat-release Red Hat Enterprise Linux Server release 5 (Tikanga)
If you are looking for a quick way and don't care what the output looks like, you can simply do this as well.
$ cat /etc/*-release DISTRIB_ID=Ubuntu DISTRIB_RELEASE=13.04 DISTRIB_CODENAME=raring DISTRIB_DESCRIPTION="Ubuntu 13.04" NAME="Ubuntu" VERSION="13.04, Raring Ringtail" ID=ubuntu ID_LIKE=debian PRETTY_NAME="Ubuntu 13.04" VERSION_ID="13.04" HOME_URL="http://www.ubuntu.com/" SUPPORT_URL="http://help.ubuntu.com/" BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"