Some Basic commands to check System status:

  • uptime – shows how long the system has been up

  • who - shows who is logged into the system

  • uname - print system information

  • runlevel – report previous and current Unix OS runlevel

uptime:

uptime is one of the basic Unix commands which allows you to quickly confirm how long your Unix system has been up and running since it was last rebooted or powered on. For Example:

[root@server]# uptime
 11:52:22 up 3 days 32 min,  4 users,  load average: 0.02, 0.04, 0.11

Details:
11:52:22 – that's the current Unix system time
up 3 days, 32 min – shows for how long your system has been running
4 users – number of users currently logged into your Unix system
load average: 0.02, 0.04, 0.11 – the average CPU load (average number of jobs in your system's run queue)for the 1, 5 and 15 minutes


who:

who is one of basic commands, which allows you to quickly see who else is logged in. When you run who without any parameters, it returns you a list of users on your Unix system, along with terminals they're using, the time of the start for each session, and the hostnames where these users are logged in from.

[root@server ~]# who
jeet     tty7         2011-06-21 11:21 (:0)
groot     tty1       2011-06-21 11:10  (:0)


uname:

uname is one of the most useful commands when it comes to gathering basic information about your system. You can use it to find out the hostname of the system you're on, the hardware architectures supported by the currently used kernel and the exact release of your system.

For Example:
1) To see the node (host) name of your system:

[root@server ~]# uname -n
server.example.com

2) To find out the hardware platform of your system:
For Linux, it will return i386 for 32-bit processors or x86_64 for 64-bit ones:

[root@server ~]# uname -i
x86_64

3) To find out the release and version of your kernel, you can use uname -r and uname -v.

[root@server ~]# uname -r
2.6.38-8-server

[root@server ~]# uname -v
#42-Ubuntu SMP Mon Apr 11 03:49:04 UTC 2011

4) You can use uname -a to output everything it knows about your system.

[root@server ~]# uname -a
Linux server 2.6.38-8-server #42-Ubuntu SMP Mon Apr 11 03:49:04 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux


runlevel:

runlevel reports the runlevel of your Linux system. runlevel command reads /var/run/utmp file and extracts the most recent login entry. It then uses this entry to extract the current and previous runlevel information from it.

For Example:

[root@server ~]# runlevel
N 5

Note: The two numbers shown are supposed to be previous and current Unix runlevels. However, the previous runlevel information is not usually found in the most recent login entry simply because runlevel hasn't changed, so the command prints "N" instead of it. Looking at the output above, you can see that the current runlevel is 5.