CPU Usage

• Note: If you are concerned about slowing the system down, you can use the nice command to lower your program's priority. For more information about the nice command, at the Unix prompt, enter:

man nice 

In Unix, you can see CPU usage on a job that is running in a number of ways, as described below:

If you want to see a grand total of CPU time for a program when it finishes running, you can use the time command. At the Unix prompt, enter:

time myprog 

Replace myprog with the name of the program you are running. The following is an output example for users in the csh or tcsh shells:

1.406u 0.042s 0:04.96 29.0% 2+5k 0+1io 0pf+0w 

The program myprog used 1.406 seconds of user time, 0.042 seconds of system time, and 4.96 seconds of real time. The sum of the user and system times is the total CPU time of the process. The percentage (29.0%) indicates the percentage of the CPU's time that the process used while it ran. The output will appear in a slightly different format when using sh, ksh, or bash, since the time command is not built into those shells.

You can also use the Unix command ps. At the Unix prompt, enter:

ps -u username 

Replace username with your username. You will see something like the following:

  PID TTY   TIME COMMAND
10005   ?   3:03  a.out
15852  rb   0:01 -tcsh (tcsh)
24980  rb   0:00 sh -c /usr/local/bin/emacs /usr1/mmouse/snd.18106
24981  rb   0:02 /usr/local/bin/emacs /usr1/mmouse/snd.18106
22311  rf   0:22 elm 

In this example, the “TIME” column shows that the process running Elm has used 22 CPU seconds.

You may also use the top command. At the Unix prompt, enter:

top 

You will see something similar to the following:

PID USERNAME PRI NICE   SIZE   RES STATE   TIME   WCPU    CPU COMMAND
28000 mmouse    96    4   276K  144K run   292:20 16.80% 16.80% desert.exe
27999 mmouse    96    4   276K  144K run   292:42 16.02% 16.02% denver.exe
19004 goofy     96    4   428K  160K run   357:11 15.63% 15.63% diskr

User mmouse is at the top of the list, and the “TIME” column shows that the program desert.exe has used 292 minutes and 20 seconds of CPU time. This is the most interactive way to see CPU usage.