uname -r
You should receive a result similar to the following:
2.6.32-431.11.2.el6.x86_64
The output can be interpreted with the following key:
2 – Kernel Version
6 – Major Revision
32 – Minor Revision
431.11.2.el6 – Fix/Revision Detail
Per the manual page, uname can also give the following information:
-a, --all print all information
-s, --kernel-name print the kernel name
-n, --nodename print the network node hostname
-r, --kernel-release print the kernel release
-v, --kernel-version print the kernel version
-m, --machine print the machine hardware name
-p, --processor print the processor type or "unknown"
-i, --hardware-platform print the hardware platform or "unknown"
-o, --operating-system print the operating system
--help display this help and exit
--version output version information and exit