Introduction to Process Management
Processes on computer systems are nothing but the applications or programs which are running.
In this lesson we will learn how to see those processes, manage processes i.e kill, change priorities etc
Lets start with the ps command
ps
ps gives you the information of all the current processes running in the system
lets see some of the examples
dbit@Tayyabali:~$ ps
PID TTY TIME CMD
29600 pts/1 00:00:00 bash
29609 pts/1 00:00:00 ps
As you can see it displays Process ID (PID), Terminal (TTY) from which its running and time(TIME) since process has been running CMD is nothing but command which started this process.
To see all the processes started by all users you can use -A option. You can also use -e option to do the same job as -A
dbit@Tayyabali:~$ ps -A
PID TTY TIME CMD
1 ? 00:00:02 systemd
2 ? 00:00:00 kthreadd
3 ? 00:00:00 rcu_gp
4 ? 00:00:00 rcu_par_gp
6 ? 00:00:00 kworker/0:0H-events_highpri
9 ? 00:00:00 mm_percpu_wq
As you can notice PID 1 is for system processes which started the OS itself
You can also use ps -ax to see all the processes running. This is BSD format, it will also show the state of the process
dbit@Tayyabali:~$ ps -ax
PID TTY STAT TIME COMMAND
1 ? Ss 0:02 /sbin/init splash
2 ? S 0:00 [kthreadd]
3 ? I< 0:00 [rcu_gp]
4 ? I< 0:00 [rcu_par_gp]
6 ? I< 0:00 [kworker/0:0H-events_highpri]
To see more information of process you can also use ps aux which will give you information about user who started it, how much is memory consumption etc
You can get more information about various advanced options using man command
You can following command
List processes by user
ps -u user
Display certain columns
ps -e -o pid,uname,pcpu,pmem,comm
Display how much time process is running, run these command and find out meaning of each option we have specified
ps -e -o pid,comm,etime
pstree
This command is useful if you find out the processes relationships, You can clearly see the parent and child processes.
dbit@Tayyabali:~$ pstree
systemd─┬─ModemManager───2*[{ModemManager}]
├─NetworkManager───2*[{NetworkManager}]
├─accounts-daemon───2*[{accounts-daemon}]
├─acpid
├─avahi-daemon───avahi-daemon
├─bluetoothd
├─boltd───2*[{boltd}]
├─colord───2*[{colord}]
├─containerd───14*[{containerd}]
You can use various options like ps -t to display threads information, ps -p to display the process ids.
You can also see the owners of the processes using -u option.
If you want to process tree of a specific user then use ps username.
nice and renice
Nice command allows you to change the priority of the process. Every process have a scheduling priority in the system. Using the nice command you can change the scheduling priority of the process.
Simple way to check the nice value of the process is to use top or htop command as shown below
top - 13:36:36 up 4:36, 1 user, load average: 0.71, 1.03, 0.90
Tasks: 344 total, 1 running, 343 sleeping, 0 stopped, 0 zombie
%Cpu(s): 2.6 us, 0.7 sy, 0.0 ni, 96.5 id, 0.1 wa, 0.0 hi, 0.0 si, 0.0 st
MiB Mem : 15702.4 total, 5945.5 free, 3563.7 used, 6193.3 buff/cache
MiB Swap: 37275.0 total, 37275.0 free, 0.0 used. 11011.6 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
33697 dbit 20 0 24.4g 157768 99700 S 16.6 1.0 1:07.02 chrome
1891 dbit 20 0 5481220 329456 112620 S 6.3 2.0 9:35.99 gnome-shell
1756 dbit 20 0 627652 112860 70404 S 4.6 0.7 7:21.56 Xorg
28603
As you can see in fourth column nice value is 0 for process 33697 process ID
You can also check NI value using ps -l
dbit@Tayyabali:~$ ps -l
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
0 S 1000 30108 28603 0 80 0 - 4911 do_wai pts/2 00:00:00 bash
4 R 1000 37432 30108 0 80 0 - 5013 - pts/2 00:00:00 ps
Highest priority process can have -20 and lowest can have +19, default priority fr user created process is 0
You can check default nice value set for you using simple nice command also as shown below
dbit@Tayyabali:~$ nice
0
You can set the nice value as shown below
dbit@Tayyabali:~$ nice -10 firefox
Firefox process will be started with 10 nice value you can verify it using
dbit@Tayyabali:~$ ps -l
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
0 S 1000 21012 21004 0 80 0 - 2753 do_wai pts/0 00:00:00 bash
4 S 1000 21019 21012 4 90 10 - 871423 poll_s pts/0 00:00:06 firefox
4 S 1000 21088 21019 0 90 10 - 49607 poll_s pts/0 00:00:00 Socket Process
4 S 1000 21121 21019 0 90 10 - 608625 poll_s pts/0 00:00:01 Privileged Cont
4 S 1000 21197 21019 0 90 10 - 607810 poll_s pts/0 00:00:00 WebExtensions
4 S 1000 21261 21019 0 90 10 - 598673 poll_s pts/0 00:00:00 Web Content
4 S 1000 21264 21019 0 90 10 - 598673 poll_s pts/0 00:00:00 Web Content
4 S 1000 21268 21019 0 90 10 - 598673 poll_s pts/0 00:00:00 Web Content
4 R 1000 21650 21012 0 80 0 - 2854 - pts/0 00:00:00 ps
You can start the process with a specified priority but what if you want to change the priority of already running process, to do this we use renice command
renice: failed to set priority for 21954 (process ID): Permission denied
dbit@Tayyabali:~$ sudo renice -n -10 -p 21954
[sudo] password for dbit:
21954 (process ID) old priority 10, new priority -10
Note you need sudoers permission to use this command
-n is to specify the priority and -p is specify the process id of the running process.
kill
Kill command is siply used to terminate the running processes. You need to know the process id to kill the process.
Using ps aux and filtering it easily find out the process ID or you can also make use of pidof command with application name to find out pid of process
as shown below
dbit@Tayyabali:~$ pidof firefox
24002 23998 23995 23922 23874 23845 23778
dbit@Tayyabali:~$ pidof gedit
24182
dbit@Tayyabali:~$ pidof chrome
24198 24061 22974 22959 22944 22915 22873 22859 22835 22819 22805 22783 22756 22739 22733 22728 22709 22696 22679 22664 22651 22630 22577 22557 4126 3989 3976 3956 3812 3801 3799 3777 3773 3772 3756
Finding PID Using grep and filter
dbit@Tayyabali:~$ ps au | grep "chrome"
dbit 24436 0.0 0.0 8908 720 pts/0 S+ 06:27 0:00 grep --color=auto chrome
dbit@Tayyabali:~$ ps au | grep "gedit"
dbit 24481 0.0 0.0 8908 656 pts/0 S+ 06:28 0:00 grep --color=auto gedit
To kill simply use kill and PID
dbit@Tayyabali:~$ pidof gedit
24182
dbit@Tayyabali:~$ kill 24182
pkill
pkill works similar to kill but it takes the name of the progrma instead of the process id
dbit@Tayyabali:~$ pkill gedit
killall
killall like other kill commands will kill all the process matching the name of the processes
dbit@Tayyabali:~$ killall chrome
Note kill commands kills only one process whereass killall kills multiple processes
xkill
xkill is used to kill the graphical applications
when run on the terminal it allows you to select the window and kill it using the mouse.
bg, fg and jobs
bg command is used to send the job in the background fg is to get the job in the foreground and jobs will display all the jobs which are currently running in the background
Lets do some experiments
Step 1 : Start applications or processes from the terminal
dbit@Tayyabali:~$ gedit
It will open gedit application but in the foreground. The teminal is occupied so lets stop the application using Ctr + Z and then
execute the bg command to put it in the background
as shown below
dbit@Tayyabali:~$ gedit
^Z
[1]+ Stopped gedit
dbit@Tayyabali:~$ bg
[1]+ gedit &
dbit@Tayyabali:~$ jobs
[1]+ Running gedit &
You can see the [1] job is running in the background
similarly we can put the firefox in the background and then we use jobs command to see how many jons are running in the background
``` dbit@Tayyabali:~$ firefox ATTENTION: default value of option mesa_glthread overridden by environment. ^Z [2]+ Stopped firefox
dbit@Tayyabali:~$ bg [2]+ firefox &
dbit@Tayyabali:~$ jobs [1]- Running gedit & [2]+ Running firefox &
```
You can now bring the any application using the number into foreground
using following command
dbit@Tayyabali:~$ fg 1
gedit
pgrep
pgrep command is used to find the process Id matching the supplied name
following are the some of the examples
dbit@Tayyabali:~$ pgrep firefox
38270
dbit@Tayyabali:~$ pgrep code
4224
4232
4233
4235
4262
4272
4291
4330
4352
4373
4426
4472
dbit@Tayyabali:~$ pgrep terminal
38719
We can also use the -u option to specify the user whose processes we care interested in
dbit@Tayyabali:~$ pgrep -u dbit terminal
38719