AS you know Linux is multitasking and multiuser systems, you can run multiple precesses processes at the same time without interfering with each other.
Process: In Linux, a running instance of a program is called process. We can say the process is a fundamental concept of the Linux OS. In other words, You can say “A process is an executing instance of a program and carry out different tasks within the operating system”.
Occasionally, when you are working on a Linux machine, you can find out easily by using ps command in Linux “what processes are currently running on your machine”.
You can use, multiple commands to view process, for example, ps command, top command, and pstree command.
ps command in Linux with Examples
In this article I am going describe ps command in Linux with examples, Ps command is used to view information with the processes on a system that stands as an abbreviation for “Process Status”.
You can use ps command to list the currently running processes with their PIDs and some other information depends on different options.
Process information is saved in /proc location as virtual files. ps command reads the process information from the virtual files from /proc file-system.
Basic Syntax of ps command in Linux
Have a look on basic syntax of ps command before start exploring it. basic syntax is as follows:
ps [OPTIONS]
You can use ps command without arguments to displays processes for the current shell. Just type ps in the terminal and hit enter, you will get all processes on the screen.
[vijay@localhost ~]$ ps PID TTY TIME CMD 3589 pts/0 00:00:00 bash 4211 pts/0 00:00:00 ps [vijay@localhost ~]$
You can see the following information from above results:
PID – the unique process ID.
TTY – the terminal type that the user is logged into.
TIME – the amount of CPU in minutes and seconds that the process has been running.
CMD – the name of the command that launched the process.
Note – Sometimes when we execute ps command, it shows TIME as 00:00:00. It is nothing but the total accumulated CPU utilization time for any process and 00:00:00 indicates no CPU time has been given by the kernel till now. In the above example, we found that for bash no CPU time has been given. This is because bash is just a parent process for different processes that need bash for their execution and bash itself is not utilizing any CPU time till now.
Print all active processes on the screen:
If you want to print all the running processes on the screen, use -A or -e option with ps command. See the example below:
[vijay@localhost ~]$ ps -e
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-kblockd
7 ? 00:00:00 kworker/u2:0-events_unbound
8 ? 00:00:00 mm_percpu_wq
9 ? 00:00:00 ksoftirqd/0
10 ? 00:00:00 rcu_sched
11 ? 00:00:00 migration/0
12 ? 00:00:00 watchdog/0
13 ? 00:00:00 cpuhp/0
15 ? 00:00:00 kdevtmpfs
16 ? 00:00:00 netns
17 ? 00:00:00 kauditd
18 ? 00:00:00 khungtaskd
19 ? 00:00:00 oom_reaper
20 ? 00:00:00 writeback
21 ? 00:00:00 kcompactd0
22 ? 00:00:00 ksmd
23 ? 00:00:00 khugepaged
[vijay@localhost ~]$ ps -A
PID TTY TIME CMD
1 ? 00:00:03 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-kblockd
7 ? 00:00:00 kworker/u2:0-events_unbound
8 ? 00:00:00 mm_percpu_wq
9 ? 00:00:00 ksoftirqd/0
10 ? 00:00:00 rcu_sched
11 ? 00:00:00 migration/0
12 ? 00:00:00 watchdog/0
13 ? 00:00:00 cpuhp/0
View Processes not associated with a terminal
View all processes except both session leaders and processes not associated with a terminal.
ps -a
[vijay@localhost ~]$ ps -a PID TTY TIME CMD 2032 tty1 00:00:00 gnome-session-b 2045 tty1 00:00:04 gnome-shell 2076 tty1 00:00:00 Xwayland 2094 tty1 00:00:00 ibus-daemon 2097 tty1 00:00:00 ibus-dconf 2100 tty1 00:00:00 ibus-x11 2138 tty1 00:00:00 gsd-xsettings 2140 tty1 00:00:00 gsd-a11y-settin 2143 tty1 00:00:00 gsd-clipboard 2145 tty1 00:00:00 gsd-color 2150 tty1 00:00:00 gsd-datetime 2152 tty1 00:00:00 gsd-housekeepin 2157 tty1 00:00:00 gsd-keyboard
You can use -d option to view all the processes except session leaders. Use syntax as follows:
$ps -d
[vijay@localhost ~]$ ps -d
PID TTY TIME CMD
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-kblockd
7 ? 00:00:00 kworker/u2:0-events_unbound
8 ? 00:00:00 mm_percpu_wq
9 ? 00:00:00 ksoftirqd/0
10 ? 00:00:00 rcu_sched
11 ? 00:00:00 migration/0
12 ? 00:00:00 watchdog/0
13 ? 00:00:00 cpuhp/0
15 ? 00:00:00 kdevtmpfs
16 ? 00:00:00 netns
Let,s view all processes except those that fulfill the specified conditions (negates the selection) :
For the Example – If you want to see only session leaders and processes not associated with a terminal. Then, run the following syntax:
ps -a -N
OR
ps -a –deselect
[vijay@localhost ~]$ ps -a --deselect
PID TTY TIME CMD
1 ? 00:00:03 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-kblockd
7 ? 00:00:00 kworker/u2:0-events_unbound
8 ? 00:00:00 mm_percpu_wq
9 ? 00:00:00 ksoftirqd/0
10 ? 00:00:00 rcu_sched
It’s time to print all processes associated with this terminal, So you can -T option to do this :
ps -T
[vijay@localhost ~]$ ps -T PID SPID TTY TIME CMD 4967 4967 pts/0 00:00:00 bash 5703 5703 pts/0 00:00:00 ps [vijay@localhost ~]$
You can view all the running processes, by using -r option :
ps -r
[vijay@localhost ~]$ ps -r PID TTY STAT TIME COMMAND 5766 pts/0 R+ 0:00 ps -r [vijay@localhost ~]$
View all processes owned by you : Processes i.e same EUID as ps which means runner of the ps command, vijay in mine case –
ps -x
[vijay@localhost ~]$ ps -x PID TTY STAT TIME COMMAND 2306 ? Ss 0:00 /usr/lib/systemd/systemd --user 2316 ? S 0:00 (sd-pam) 2324 ? S 0:00 /usr/bin/pulseaudio --daemonize=no 2330 ? Sl 0:00 /usr/bin/gnome-keyring-daemon --daemonize --login 2337 ? Ssl 0:00 /usr/bin/dbus-daemon --session --address=systemd: --n 2342 tty2 Ssl+ 0:00 /usr/libexec/gdm-wayland-session gnome-session 2348 tty2 Sl+ 0:00 /usr/libexec/gnome-session-binary 2410 tty2 Sl+ 2:45 /usr/bin/gnome-shell 2428 ? Ssl 0:00 /usr/libexec/gvfsd