The top Command

You can monitor the amount of memory and CPU resources your system is using with the top command:

     [root@bigboy tmp]# top
     top - 20:00:54 up 61 days, 23:35, 2 users, load average: 0.00, 0.00
     Tasks: 72 total, 1 running, 71 sleeping, 0 stopped, 0 zombie
     Cpu(s): 4.3% us, 0.5% sy, 0.0% ni, 95.1% id, 0.1% wa, 0.0% hi,
     Mem:  1027784k total, 868484k used,  159300k free, 276272k
     Swap: 4192924k total,     80k used, 4192844k free, 356256k
     PID USER PR NI VIRT RES   SHR  S %CPU %MEM TIME+   COMMAND
       1 root 16  0 2268 516  1420  S  0.0  0.1 0:03.85 init
       2 root 34 19    0   0     0  S  0.0  0.0 0:00.32 ksoftirqd/0
       3 root 5 -10    0   0     0  S  0.0  0.0 0:00.00 events/0
       4 root 7 -10    0   0     0  S  0.0  0.0 0:00.02 khelper
     [root@bigboy tmp]#

Here the CPU usage is running 95.1% idle and 15% of memory (159300k) is free. The amount of free memory may appear low, but in this case, the server doesn't seem to be swapping idle processes from memory to the swap disk partition as it isn't being used at all. Excessive swapping can cause your system to slow down dramatically, the simplest ways to avoid this is to add more RAM or reduce the number of processes or users that are active on your system.

If your system seems slow but the CPU and memory usage is low, then start looking at networking problems, such as poor duplex negotiation, bad cables, and network congestion due to excessive traffic.