1. The kernel name (-s)
2. The Network node hostname (-n)
3. The kernel release (-r)
4. The kernel version (-v)
5. The machine hardware name (-m)
6. The processor type (-p)
7. The hardware platform (-i)
8. The operating system (-o)

CentOS / RHEL 6.x find kernel version command

Open a command-line terminal (select Applications > Accessories > Terminal), OR login to remote server using the ssh command and then type:
$ uname -r
Sample outputs:

2.6.32-220.2.1.el6.x86_6

The following provides a little more information:
$ uname -mrs
Sample outputs:

Linux 2.6.32-220.2.1.el6.x86_64 x86_64

You can see the complete information with the following command:
$ uname -a
Sample outputs:

Linux example.cyberciti.biz 2.6.32-220.2.1.el6.x86_64 #1 SMP Tue Dec 13 16:21:34 EST 2011 x86_64 x86_64 x86_64 GNU/Linux

The above output indicates that I am running kernel version 2.6.32. The number 220.2.1 indicates additional info such as security or bug fix kernel revision.

Find Red Hat Linux or CentOS Linux distribution version

Type the following cat command:
$ cat /etc/redhat-release
Sample outputs:

Red Hat Enterprise Linux Server release 6.2 (Santiago)

Or you can use lsb_release command as follows:
$ lsb_release -a
Sample outputs:

LSB Version:	:base-4.0-amd64:base-4.0-noarch:core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
Distributor ID:	RedHatEnterpriseServer
Description:	Red Hat Enterprise Linux Server release 6.4 (Santiago)
Release:	6.4
Codename:	Santiago

The lsb_release command supports the following options:

       -v, --version

              Display the version of the LSB specification against  which  the
              distribution is compliant.

       -i, --id

              Display the string id of the distributor.

       -d, --description

              Display the single line text description of the distribution.

       -r, --release

              Display the release number of the distribution.

       -c, --codename

              Display the codename according to the distribution release.

       -a, --all

              Display all of the above information.

       -s, --short

              Use  short  output  format  for  information  requested by other
              options (or version if none).

/etc/issue file

You can use /etc/issue file. But, many sysadmin customize this file. So I recommned that you only use uname command:

cat /etc/issue
 
Red Hat Enterprise Linux Server release 6.5 (Santiago)
Kernel \r on an \m

Related media

This tutorial is also available in a quick video format:

Putting it all together