It’s somewhat trivial job to get details about how much of CPU time is consumed by Linux OSs, its parts or numerous software it runs, but fortunately there are numerous utilities making it doable to get it. A few of them are included into sure Linux distribution, other are not however most of tools listed below can be used to find out CPU utilization stats:
1. top
top is very old and important core utility coming with almost any Linux and Unix operating systems. It shows real-time system resources utilization (CPU, RAM, swap file etc.) to administrators via console, here is the part of it’s output:
top - 16:05:38 up 3 days, 6:08, 2 users, load average: 0.54, 0.54, 0.61
Tasks: 100 total, 2 running, 98 sleeping, 0 stopped, 0 zombie
Cpu(s): 5.3%us, 1.0%sy, 0.0%ni, 93.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 515984k total, 497928k used, 18056k free, 13988k buffers
Swap: 1502068k total, 92956k used, 1409112k free, 129096k cached
As this tool provides a lot of useful information, it makes sense to read its manual page: type man top.
2. atsar
sar, atsar are other old tools providing system activity reports including CPU load we need. Here is an example of sar’s usage:
viper@viper-desktop:~$ sar -u 2 5
Linux viper-desktop 2.6.20-17-generic #2 SMP Mon Jun 9 22:08:13 UTC 2008 i686 07/04/2008
16:13:58 cpu %usr %nice %sys %irq %softirq %wait %idle _cpu_
16:14:00 all 3 0 0 0 0 1 97
16:14:02 all 0 0 0 0 0 0 99
16:14:04 all 0 0 0 0 0 0 100
16:14:06 all 23 0 0 0 0 0 76
16:14:08 all 0 0 0 0 0 0 100
As you might see CPU utilization was almost 0% for two seconds after the command was executed. BTW, here is the description of the options sar was started with:
-u showed statistics about CPU utilization (average and per cpu) with 5 intervals of 2 seconds.
3. ps
ps is one the most used core utilities every Linux or Unix administrator uses as this utility with short name shows processes run in the system. If you need to get information about how much CPU or RAM resources are consumed by certain process, just run this:
viper@viper-desktop:~$ ps u 23988
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
viper 23988 0.0 0.6 5760 3280 pts/0 Ss 15:54 0:00 bash
where 23988 is PID of the process (can be get from the output of ps ax).
And be sure look the manual of those commands for ore details.
