In server administration, it’s crucial to have a comprehensive understanding of your system’s activity. This knowledge allows you to optimize performance, troubleshoot issues, and ensure the smooth operation of your web server.
One of the most effective tools for this purpose is the top command, a utility that provides a dynamic, real-time view of a running system. It displays system summary information as well as a list of tasks currently managed by the Linux kernel.
This guide will walk you through the usage of the top command on CentOS 5/CentOS 6/RHEL 5/ RHEL 6 servers.
For a more in-depth understanding of web server types, you may want to explore our articles on Apache, Nginx, and LiteSpeed. Understanding the type of server you’re working with can greatly enhance your ability to optimize and troubleshoot it.
Using the `top` Command
The top command is a utility that allows you to monitor system activity interactively. When you run top from a shell window, it displays all active processes and updates the screen in real time. This is particularly useful for keeping track of system activity and optimizing system performance.
To display the top command on RHEL 6, you would use the following command:
[root@rhel6 ~]# top
This will display a variety of information, including the total number of tasks, the number of running tasks, CPU usage, memory usage, and a list of all active processes.
[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
Adjusting the Update Interval
By default, top will update its screen every second. However, you can change this interval by using the d option followed by the number of seconds you want as the new interval. For example, to update the screen every 5 seconds, you would use the following command:
[root@rhel6 ~]# top d 5
[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, you would use:
[root@rhel6 ~]# top d 10
[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
Updating the screen at an interval of 5 to 20 seconds is often more useful than the default setting of 1 second. This is because when top updates every second, it often lists itself in its own output as the main resource consumer.
Getting Help
If you need help while using top, you can press the h key while top is running to display a help screen.
Z,B,E,e Global: 'Z' colors; 'B' bold; 'E'/'e' summary/task memory scale l,t,m Toggle Summary: 'l' load avg; 't' task/cpu stats; 'm' memory info 0,1,2,3,I Toggle: '0' zeros; '1/2/3' cpus or numa node views; 'I' Irix mode f,F,X Fields: 'f'/'F' add/remove/order/sort; 'X' increase fixed-width L,&,<,> . Locate: 'L'/'&' find/again; Move sort column: '<'/'>' left/right R,H,V,J . Toggle: 'R' Sort; 'H' Threads; 'V' Forest view; 'J' Num justify c,i,S,j . Toggle: 'c' Cmd name/line; 'i' Idle; 'S' Time; 'j' Str justify x,y . Toggle highlights: 'x' sort field; 'y' running tasks z,b . Toggle: 'z' color/mono; 'b' bold/reverse (only if 'x' or 'y') u,U,o,O . Filter by: 'u'/'U' effective/any user; 'o'/'O' other criteria n,#,^O . Set: 'n'/'#' max tasks displayed; Show: Ctrl+'O' other filter(s) C,... . Toggle scroll coordinates msg for: up,down,left,right,home,end k,r Manipulate tasks: 'k' kill; 'r' renice d or s Set update interval W,Y Write configuration file 'W'; Inspect other output 'Y' q Quit
Commands Mentioned
- top – Displays real-time system activity
- top -d [seconds] – Changes the update interval of `top`
Conclusion
The top command is a powerful tool for server administrators, providing a real-time view of system activity and allowing for the optimization of system performance. By understanding how to use this command and adjust its settings, you can gain a comprehensive understanding of your server’s activity.
This knowledge is crucial for troubleshooting issues, optimizing performance, and ensuring the smooth operation of your server. Whether you’re working with a dedicated server, a VPS server, cloud hosting, or shared hosting, mastering the top command is a valuable skill for any webmaster or website administrator.
Remember, the key to effective server administration is not just about knowing the right commands, but understanding how to interpret the data they provide. With the top command, you have a powerful tool at your disposal to monitor, analyze, and optimize your server’s performance.
Happy server managing!
FAQ
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What is the `top` command used for?
The `top` command is used to monitor system activity interactively. It provides a dynamic, real-time view of a running system, displaying system summary information and a list of tasks currently managed by the Linux kernel. This is particularly useful for keeping track of system activity and optimizing system performance.
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How can I change the update interval of the `top` command?
You can change the update interval of the `top` command by using the `d` option followed by the number of seconds you want as the new interval. For example, `top -d 5` will update the screen every 5 seconds.
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Why is it recommended to change the update interval of the `top` command?
Changing the update interval of the `top` command can prevent it from listing itself in its own output as the main resource consumer, which often happens when `top` updates every second (the default setting). Updating the screen at an interval of 5 to 20 seconds can provide a more useful view of system activity.
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What information does the `top` command display?
The `top` command displays a variety of information, including the total number of tasks, the number of running tasks, CPU usage, memory usage, and a list of all active processes. This information is updated in real time (or at the interval specified with the `d` option).
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How can I get help while using the `top` command?
If you need help while using the `top` command, you can press the `h` key while `top` is running to display a help screen. This screen provides a summary of the command’s options and how to use them.
