103.6. Modify process execution priorities
Weight: 2
Candidates should be able to manage process execution priorities.
Objectives
- Know the default priority of a job that is created.
- Run a program with higher or lower priority than the default..
- Change the priority of a running process.
- nice
- ps
- renice
- top
On a Linux system, we are running a lot of processes and programs on a few CPUs. So you need a way to tell your OS to give more priority to some tasks or give less resources to some others. In last section you saw the top command to check the CPU usage of each process:
$ top
top - 08:44:51 up 13:00, 5 users, load average: 0.57, 1.50, 1.50
Tasks: 290 total, 2 running, 288 sleeping, 0 stopped, 0 zombie
%Cpu(s): 38.4 us, 9.4 sy, 0.0 ni, 49.3 id, 2.8 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem: 8060264 total, 7858348 used, 201916 free, 360144 buffers
KiB Swap: 7811068 total, 0 used, 7811068 free. 2842344 cached Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
13605 jadi 25 5 1473652 530700 91128 R 54.5 6.6 3:25.50 firefox
11157 root 20 0 572004 112652 94484 S 6.1 1.4 3:26.18 Xorg
12265 jadi 20 0 1210484 75848 42264 S 6.1 0.9 0:32.06 Telegram
12671 jadi 20 0 1800508 274564 80300 S 6.1 3.4 1:27.35 compiz
15035 jadi 20 0 768688 54920 34228 S 6.1 0.7 0:00.93 /usr/bin/termin
15066 jadi 20 0 33796 3076 2448 R 6.1 0.0 0:00.02 top
1 root 20 0 29528 4320 2584 S 0.0 0.1 0:02.27 init
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root 20 0 0 0 0 S 0.0 0.0 0:00.27 ksoftirqd/0
5 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H ```
Chkecn th
There is NI column, it shows how nice the process is. The nicer the process, the less CPU it asks. Nice can be from -20 to 19 (a process with nice = -20 is ANGRY and asking for a lot of CPU while a process with nice = 19 is SUPER NICE and lets other processes use most of the CPU).
If you do not use nice command, processes will have nice level of 0. This can be checked with
nicecommand:$ nice 0
It is also possible to tell ps command to write the nice parameter of processes:
$ ps -l
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
0 S 1000 15044 15035 0 80 0 - 7453 wait pts/29 00:00:00 bash
0 S 1000 15052 15044 0 60 -20 - 3976 hrtime pts/29 00:00:00 sleep
0 R 1000 15080 15044 0 80 0 - 4680 - pts/29 00:00:00 ps
Setting priorities when running commands
If you need to change the niceness level of a program you can running it with nice command and -n switch (for nice):
$ nice -n -20 echo "I am running!"
nice: cannot set niceness: Permission denied
I am running!
$ sudo nice -n -20 echo "I am running!"
I am running!
$ sudo nice -n 19 echo "I am running!"
I am running!
Please note to two points:
- Give high priorities (less than 0) needs root access
- If you are not root and asking for nice level lower than 0 you'll get an error message but the process will run with normal nice level (0).
If you run a command with nice without any parameters, the nice value will be 10:
$ nice xeyes &
[1] 15217
$ ps -l
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
0 S 1000 15044 15035 0 80 0 - 7455 wait pts/29 00:00:00 bash
0 S 1000 15217 15044 0 90 10 - 12522 poll_s pts/29 00:00:00 xeyes
0 R 1000 15218 15044 0 80 0 - 4680 - pts/29 00:00:00 ps
Changing priorities
The renice command can change the niceness of running processes:
$ ps -ef | grep firefox
jadi 13605 11226 30 08:28 ? 00:10:13 /usr/lib/firefox/firefox
jadi 15192 15044 0 09:01 pts/29 00:00:00 grep firefox
$ sudo renice -n -10 13605
13605 (process ID) old priority 5, new priority -10
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