Operating System OS Version Commands

Linux:

[root@myod~]# cat /proc/version
Linux version 2.6.32-220.el6.x86_64 (mockbuild@x86-004.build.bos.redhat.com) (gcc version 4.4.5 20110214 (Red Hat 4.4.5-6) (GCC) ) #1 SMP Wed Nov 9 08:03:13 EST 2011
[root@myod ~]#

AIX:

oslevel -s : shows the current status Service Pack of the OS.

root@orange-lpar:/ #oslevel -s
7100-00-01-1037
root@orange-lpar:/ #

The service pack level returned is in the format 7100-00-01-1037, 
where 7100 refers to base level 7.1.0.0; 
00 refers to technology level 0; 
01 refers to service pack 1; 
1037 refers to the yyww build date in year and weeks, 
in this case, the 37th week of the year 2010 

oslevel -r : determines the highest technology level reached for the current version of AIX(R) on the system

Solaris:

# uname -r
5.10

HP-UX:

uname -a
HP-UX  bmd350  B.10.20  D 9000/831  2011043966  64-user license

This example shows HP-UX running the 10.20 version