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Linux System Administrator's Guide

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7.1.1. The top command.

The most common of these commands is top . The top will display a continually updating report of system resource usage.


   

 # top
  12:10:49 up 1 day, 3:47, 7 users, load average: 0.23, 0.19, 0.10
 125 processes: 105 sleeping, 2 running, 18 zombie, 0 stopped
 CPU states: 5.1% user 1.1% system 0.0% nice 0.0% iowait 93.6% idle
 Mem: 512716k av, 506176k used, 6540k free, 0k shrd, 21888k buff
 Swap: 1044216k av, 161672k used, 882544k free 199388k cached
 
 PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME CPU COMMAND
 2330 root 15 0 161M 70M 2132 S 4.9 14.0 1000m 0 X
 2605 weeksa 15 0 8240 6340 3804 S 0.3 1.2 1:12 0 kdeinit
 3413 weeksa 15 0 6668 5324 3216 R 0.3 1.0 0:20 0 kdeinit
 18734 root 15 0 1192 1192 868 R 0.3 0.2 0:00 0 top
 1619 root 15 0 776 608 504 S 0.1 0.1 0:53 0 dhclient
 1 root 15 0 480 448 424 S 0.0 0.0 0:03 0 init
 2 root 15 0 0 0 0 SW 0.0 0.0 0:00 0 keventd
 3 root 15 0 0 0 0 SW 0.0 0.0 0:00 0 kapmd
 4 root 35 19 0 0 0 SWN 0.0 0.0 0:00 0 ksoftirqd_CPU0
 9 root 25 0 0 0 0 SW 0.0 0.0 0:00 0 bdflush
 5 root 15 0 0 0 0 SW 0.0 0.0 0:00 0 kswapd
 10 root 15 0 0 0 0 SW 0.0 0.0 0:00 0 kupdated
 11 root 25 0 0 0 0 SW 0.0 0.0 0:00 0 mdrecoveryd
 15 root 15 0 0 0 0 SW 0.0 0.0 0:01 0 kjournald
 81 root 25 0 0 0 0 SW 0.0 0.0 0:00 0 khubd
 1188 root 15 0 0 0 0 SW 0.0 0.0 0:00 0 kjournald
 1675 root 15 0 604 572 520 S 0.0 0.1 0:00 0 syslogd
 1679 root 15 0 428 376 372 S 0.0 0.0 0:00 0 klogd
 1707 rpc 15 0 516 440 436 S 0.0 0.0 0:00 0 portmap
 1776 root 25 0 476 428 424 S 0.0 0.0 0:00 0 apmd
 1813 root 25 0 752 528 524 S 0.0 0.1 0:00 0 sshd
 1828 root 25 0 704 548 544 S 0.0 0.1 0:00 0 xinetd
 1847 ntp 15 0 2396 2396 2160 S 0.0 0.4 0:00 0 ntpd
 1930 root 24 0 76 4 0 S 0.0 0.0 0:00 0 rpc.rquotad 

The top portion of the report lists information such as the system time, uptime, CPU usage, physical ans swap memory usage, and number of processes. Below that is a list of the processes sorted by CPU utilization.

You can modify the output of top while is is running. If you hit an i , top will no longer display idle processes. Hit i again to see them again. Hitting M will sort by memory usage, S will sort by how long they processes have been running, and P will sort by CPU usage again.

In addition to viewing options, you can also modify processes from within the top command. You can use u to view processes owned by a specific user, k to kill processes, and r to renice them.

For more in-depth information about processes you can look in the /proc filesystem. In the /proc filesystem you will find a series of sub-directories with numeric names. These directories are associated with the processes ids of currently running processes. In each directory you will find a series of files containing information about the process.

YOU MUST TAKE EXTREME CAUTION TO NOT MODIFY THESE FILES, DOING SO MAY CAUSE SYSTEM PROBLEMS!

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