Top command is utility to monitor system activity interactively. When you run top from shell window, it will display all the activity processes and updates the screen. In this post i will show the usage of top command on CentOS 5/CentOS 6/RHEL 5/ RHEL 6 server to keep track system activity and to optimize the system performance.
Display top command on RHEL 6 :
[root@rhel6 ~]# top
top - 18:54:19 up 13:29, 2 users, load average: 0.00, 0.00, 0.00
Tasks: 93 total, 1 running, 90 sleeping, 2 stopped, 0 zombie
Cpu(s): 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 1031320k total, 225804k used, 805516k free, 31120k buffers
Swap: 2064376k total, 0k used, 2064376k free, 116716k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1375 root 20 0 97768 9796 5768 S 0.3 0.9 0:03.43 httpd
3974 root 20 0 2632 1076 868 R 0.3 0.1 0:00.08 top
1 root 20 0 2828 1392 1196 S 0.0 0.1 0:01.81 init
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
4 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0
5 root RT 0 0 0 0 S 0.0 0.0 0:00.00 watchdog/0
6 root 20 0 0 0 0 S 0.0 0.0 0:00.25 events/0
7 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuset
8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khelper
9 root 20 0 0 0 0 S 0.0 0.0 0:00.00 netns
10 root 20 0 0 0 0 S 0.0 0.0 0:00.00 async/mgr
11 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pm
12 root 20 0 0 0 0 S 0.0 0.0 0:00.00 sync_supers
13 root 20 0 0 0 0 S 0.0 0.0 0:00.00 bdi-default
14 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kintegrityd/0
15 root 20 0 0 0 0 S 0.0 0.0 0:00.02 kblockd/0
16 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpid
17 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpi_notify
18 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpi_hotplug
19 root 20 0 0 0 0 S 0.0 0.0 0:00.01 ata/0
20 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ata_aux
21 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksuspend_usbd
22 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khubd
23 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kseriod
25 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khungtaskd
26 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kswapd0
27 root 25 5 0 0 0 S 0.0 0.0 0:00.00 ksmd
28 root 20 0 0 0 0 S 0.0 0.0 0:00.00 aio/0
29 root 20 0 0 0 0 S 0.0 0.0 0:00.00 crypto/0
34 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pciehpd
36 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kpsmoused
37 root 20 0 0 0 0 S 0.0 0.0 0:00.00 usbhid_resumer
67 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kstriped
267 root 20 0 0 0 0 S 0.0 0.0 0:00.00 scsi_eh_0
268 root 20 0 0 0 0 S 0.0 0.0 0:00.00 scsi_eh_1
279 root 20 0 0 0 0 S 0.0 0.0 0:00.20 mpt_poll_0
Display top command on CentOS 5.7 :
[root@CentOS57 ~]# top
top - 18:57:39 up 10:04, 2 users, load average: 0.00, 0.00, 0.00
Tasks: 73 total, 1 running, 70 sleeping, 2 stopped, 0 zombie
Cpu(s): 0.0%us, 0.1%sy, 0.0%ni, 99.8%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 1034700k total, 86916k used, 947784k free, 7292k buffers
Swap: 2096472k total, 0k used, 2096472k free, 36104k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 15 0 2160 676 584 S 0.0 0.1 0:00.93 init
2 root RT -5 0 0 0 S 0.0 0.0 0:00.00 migration/0
3 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0
4 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/0
5 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 khelper
6 root 20 -5 0 0 0 S 0.0 0.0 0:00.00 kthread
9 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/0
10 root 20 -5 0 0 0 S 0.0 0.0 0:00.00 kacpid
173 root 17 -5 0 0 0 S 0.0 0.0 0:00.00 cqueue/0
176 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 khubd
178 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kseriod
244 root 21 0 0 0 0 S 0.0 0.0 0:00.00 khungtaskd
245 root 22 0 0 0 0 S 0.0 0.0 0:00.00 pdflush
246 root 15 0 0 0 0 S 0.0 0.0 0:00.01 pdflush
247 root 17 -5 0 0 0 S 0.0 0.0 0:00.00 kswapd0
248 root 17 -5 0 0 0 S 0.0 0.0 0:00.00 aio/0
466 root 11 -5 0 0 0 S 0.0 0.0 0:00.00 kpsmoused
492 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 mpt_poll_0
493 root 19 -5 0 0 0 S 0.0 0.0 0:00.00 mpt/0
494 root 19 -5 0 0 0 S 0.0 0.0 0:00.00 scsi_eh_0
497 root 19 -5 0 0 0 S 0.0 0.0 0:00.00 ata/0
498 root 19 -5 0 0 0 S 0.0 0.0 0:00.00 ata_aux
505 root 20 -5 0 0 0 S 0.0 0.0 0:00.00 kstriped
514 root 10 -5 0 0 0 S 0.0 0.0 0:00.17 kjournald
544 root 11 -5 0 0 0 S 0.0 0.0 0:00.00 kauditd
577 root 21 -4 3004 1468 504 S 0.0 0.1 0:00.62 udevd
1730 root 20 -5 0 0 0 S 0.0 0.0 0:00.00 kmpathd/0
1731 root 20 -5 0 0 0 S 0.0 0.0 0:00.00 kmpath_handlerd
1790 root 11 -5 0 0 0 S 0.0 0.0 0:00.00 kjournald
1868 root 13 -5 0 0 0 S 0.0 0.0 0:00.00 iscsi_eh
1896 root 18 -5 0 0 0 S 0.0 0.0 0:00.00 cnic_wq
1911 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 ib_addr
1918 root 20 -5 0 0 0 S 0.0 0.0 0:00.00 ib_mcast
1919 root 20 -5 0 0 0 S 0.0 0.0 0:00.00 ib_inform
1920 root 20 -5 0 0 0 S 0.0 0.0 0:00.00 local_sa
1923 root 20 -5 0 0 0 S 0.0 0.0 0:00.00 iw_cm_wq
By default, top will update its screen in every seconds. You can change this interval by using d seconds options as below :
To update the screen every 5 seconds, run the “top d 5” command :
[root@rhel6 ~]# top d 5 top - 18:56:51 up 13:32, 2 users, load average: 0.00, 0.00, 0.00 Tasks: 94 total, 1 running, 90 sleeping, 3 stopped, 0 zombie Cpu(s): 0.0%us, 0.1%sy, 0.0%ni, 99.7%id, 0.2%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 1031320k total, 226064k used, 805256k free, 31136k buffers Swap: 2064376k total, 0k used, 2064376k free, 116716k cached
To update the screen every 10 seconds, run the “top d 10” command :
[root@rhel6 ~]# top d 10 top - 18:57:21 up 13:32, 2 users, load average: 0.00, 0.00, 0.00 Tasks: 95 total, 1 running, 90 sleeping, 4 stopped, 0 zombie Cpu(s): 0.0%us, 0.1%sy, 0.0%ni, 99.7%id, 0.2%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 1031320k total, 226448k used, 804872k free, 31144k buffers Swap: 2064376k total, 0k used, 2064376k free, 116716k cached
The screen updates every 5 to 20 seconds interval is more usefull tha the default setting, 1 second. This because update every 1 second will lists itself in its own output as the main resource consumer. If you press the h key while top is running, you will see the following output screen :
