We use top to continuously show the processes status, system uptime, processor loading, memory usage, etc. Normally, top doesn't need any command line options. For detailed usage, see the manpage.
e.g. Type top in the shell prompt.
[yuni@lovely-linux yuni]$ top
3:14pm up 14 days, 4:40, 6 users, load average: 0.00, 0.00, 0.00
93 processes: 82 sleeping, 1 running, 0 zombie, 10 stopped
CPU states: 0.3% user, 0.3% system, 0.0% nice, 99.2% idle
Mem: 127088K av, 124300K used, 2788K free, 0K shrd, 39528K buff
Swap: 787176K av, 9536K used, 777640K free 25852K cached
PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
3050 yuni 15 0 1192 1192 936 R 0.7 0.9 0:01 top
1 root 7 0 368 368 332 S 0.0 0.2 0:03 init
2 root 9 0 0 0 0 SW 0.0 0.0 0:00 keventd
3 root 9 0 0 0 0 SW 0.0 0.0 0:11 kswapd
4 root 9 0 0 0 0 SW 0.0 0.0 0:00 kreclaimd
5 root 9 0 0 0 0 SW 0.0 0.0 0:04 bdflush
6 root 9 0 0 0 0 SW 0.0 0.0 0:00 kupdated
In this example, the system has been up running for 14 days, with 6 users, 93 processes, 82 of which are sleeping, 1 of which is running, 10 are stopped. The total available memory is roughly 128M, nearly all (124300Kb) are used leaving 2788Kb free. The top process (the most CPU-intensive) is top itself, occupying 0.7 % of CPU load.