How to find the Linux kernel version?

The ‘uname’ command is use to determine certain system information in all the Linux/Unix flavours like CentOS,
Ubuntu, Debian, Fedora, FreeBSD etc. With specific ‘uname’ options, you can display all the details of the
current working kernel on the server.
To display the working kernel name, version, date and time, system architecture type, use:
[root@vps ~]# uname -a
Linux vps.vpsbus.net 2.6.18-238.12.1.el5.pony6-1 #3 SMP Fri Jun 3 16:37:31 PDT 2011 i686 i686 i386 GNU/Linux
To print only the kernel version along with it’s major and minor versions:
[root@vps ~]# uname -r
2.6.18-238.12.1.el5.pony6-1
To print the system architecture type i.e. whether the machine is 32 or 64 bit, use:
[root@vps ~]# uname -p
i686
The /proc/version file also contains the kernel information:
[root@vps ~]# cat /proc/version
Linux version 2.6.18-238.12.1.el5.pony6-1 (root@dev.buyvm.net) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-50)) #3