It’s rather trivial task to get information about how much of CPU time is consumed by Linux operating system, its components or various software it runs, but thankfully there are numerous utilities making it possible to get it. Some of them are included into certain Linux distribution, other aren’t but most of tools listed below can be used to find out CPU utilization statistics:
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).
Of course it makes sense to read manuals of above mentioned commands ps, top, sar, atsar, iostat. Good luck!
