In Linux you can control the priority of a process with the commands nice and renice. There are limitations if you are a non-root user. The nice and renice commands have the values in the range of -20 to +19. The higher the numbers the higher the priority, or the nicer the process is meaning the less CPU it would use, so it's kind of the opposite of what you are thinking. So it's like nice guys finished last?
So if we run the sleep process again let's see what happens by default
sleep 1500&
[root@cent7 jhuynh]# sleep 1500&
[1] 3401
[root@cent7 jhuynh]# ps -l
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
4 S 0 3358 3315 0 80 0 - 68658 poll_s pts/0 00:00:00 sudo
4 S 0 3365 3358 0 80 0 - 58056 do_wai pts/0 00:00:00 su
4 S 0 3368 3365 0 80 0 - 29107 do_wai pts/0 00:00:00 bash
4 S 0 3401 3368 0 80 0 - 27014 hrtime pts/0 00:00:00 sleep
0 R 0 3402 3368 0 80 0 - 38332 - pts/0 00:00:00 ps
As you can see the priority(PRI) is set to 80 percent by default
Now let's be a nice guy and assign the sleep process to the nicest value -19
[root@cent7 jhuynh]# nice -n 19 sleep 1500&
[2] 3438
[root@cent7 jhuynh]# ps -l
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
4 S 0 3358 3315 0 80 0 - 68658 poll_s pts/0 00:00:00 sudo
4 S 0 3365 3358 0 80 0 - 58056 do_wai pts/0 00:00:00 su
4 S 0 3368 3365 0 80 0 - 29107 do_wai pts/0 00:00:00 bash
4 S 0 3401 3368 0 80 0 - 27014 hrtime pts/0 00:00:00 sleep
4 S 0 3438 3368 0 99 19 - 27014 hrtime pts/0 00:00:00 sleep
0 R 0 3439 3368 0 80 0 - 38332 - pts/0 00:00:00 ps
As you can see the new sleep process is set to priority 99 meaning only run the process if processes with the a lower number is ran first. It's like being the 99th person in line.
If you run it at the highest nice value, not so nice. Let's see what happens
[root@cent7 jhuynh]# nice -n -20 sleep 1500&
[2] 3546
[root@cent7 jhuynh]# ps -l
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
4 S 0 3358 3315 0 80 0 - 68658 poll_s pts/0 00:00:00 sudo
4 S 0 3365 3358 0 80 0 - 58056 do_wai pts/0 00:00:00 su
4 S 0 3368 3365 0 80 0 - 29107 do_wai pts/0 00:00:00 bash
4 S 0 3543 3368 0 99 19 - 27014 hrtime pts/0 00:00:00 sleep
4 S 0 3546 3368 0 60 -20 - 27014 hrtime pts/0 00:00:00 sleep
0 R 0 3547 3368 0 80 0 - 38332 - pts/0 00:00:00 ps
You can also reassign the priority of an existing process with renice command, with the renice command you have to specify the process id
[root@cent7 jhuynh]# renice -n 5 -p 3543
3543 (process ID) old priority 19, new priority 5
[root@cent7 jhuynh]# ps -l
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
4 S 0 3358 3315 0 80 0 - 68658 poll_s pts/0 00:00:00 sudo
4 S 0 3365 3358 0 80 0 - 58056 do_wai pts/0 00:00:00 su
4 S 0 3368 3365 0 80 0 - 29107 do_wai pts/0 00:00:00 bash
4 S 0 3543 3368 0 85 5 - 27014 hrtime pts/0 00:00:00 sleep
4 S 0 3546 3368 0 60 -20 - 27014 hrtime pts/0 00:00:00 sleep
0 R 0 3589 3368 0 80 0 - 38332 - pts/0 00:00:00 ps
Linux was nice enough to tell you that the process has been changed from priority of 19 to 5, so now the process is assigned a priority value of 85. Still the nicest priority!
The caveat on the renice command is that if you are not a user with root privileges, you cannot set a higher priority than the original priority of a process.
If you are root you can also control other user's priority settings by editing the /etc/security/limits.conf. Priority is the last item or settings that you can set limits on, so move to the end of the line and type in the following for user limit, if you want group limits you just prefix it with the @ sign
#* soft core 0
#* hard rss 10000
#@student hard nproc 20
#@faculty soft nproc 20
#@faculty hard nproc 50
#ftp hard nproc 0
#@student - maxlogins 4
# End of file
techjunkie - priority 5
Now the next time techjunkie sets a priority he will be limited to priority number 5 nice value. Since he is not a root user he cannot renice the process to be anything higher than 5. Therefore he is a pretty nice guy.
No comments:
Post a Comment