As we all know Linux is a multitasking and multi-user systems. So, it allows multiple processes to operate simultaneously without interfering with each other. Process is one of the important fundamental concept of the Linux OS. A process is an executing instance of a program and carry out different tasks within the operating system.
Linux provides us a utility called ps for viewing information related with the processes on a system which stands as abbreviation for “Process Status”. ps command is used to list the currently running processes and their PIDs along with some other information depends on different options. It reads the process information from the virtual files in /proc file-system. /proc contains virtual files, this is the reason it’s referred as a virtual file system.
ps provides numerous options for manipulating the output according to our need.
Options for ps Command :
- Simple process selection : Shows the processes for the current shell –
[root@rhel7 ~]# ps PID TTY TIME CMD 12330 pts/0 00:00:00 bash 21621 pts/0 00:00:00 ps
Result contains four columns of information.
PID – the unique process ID
TTY – terminal type that the user is logged into
TIME – amount of CPU in minutes and seconds that the process has been running
CMD – 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 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 which needs bash for their execution and bash itself is not utilizing any CPU time till now.
- View Processes : View all the running processes use either of the following option with ps –
[root@rhel7 ~]# ps -A [root@rhel7 ~]# ps -e
- View Processes not associated with a terminal : View all processes except both session leaders and processes not associated with a terminal.
[root@rhel7 ~]# ps -a PID TTY TIME CMD 27011 pts/0 00:00:00 man 27016 pts/0 00:00:00 less 27499 pts/1 00:00:00 ps
Note – You may be thinking that what is session leader? A unique session is assing to evry process group. So, session leader is a process which kicks off other processes. The process ID of first process of any session is similar as the session ID.
- View all the processes except session leaders :
[root@rhel7 ~]# ps -d
- View all processes except those that fulfill the specified conditions (negates the selection) :
Example – If you want to see only session leader and processes not associated with a terminal. Then, run
[root@rhel7 ~]# ps -a -N OR [root@rhel7 ~]# ps -a --deselect
- View all processes associated with this terminal :
[root@rhel7 ~]# ps -T
- View all the running processes :
[root@rhel7 ~]# ps -r
- View all processes owned by you : Processes i.e same EUID as ps which means runner of the ps command, root in this case –
[root@rhel7 ~]# ps -x
Process selection by list
Here we will discuss how to get the specific processes list with the help of ps command. These options accept a single argument in the form of a blank-separated or comma-separated list. They can be used multiple times.
For example: ps -p “1 2” -p 3,4
- Select the process by the command name. This selects the processes whose executable name is given in cmdlist. There may be a chance you won’t know the process ID and with this command it is easier to search.
Syntax : ps -C command_name
Syntax : ps -C command_name Example : [root@rhel7 ~]# ps -C dhclient PID TTY TIME CMD 19805 ? 00:00:00 dhclient
- Select by group ID or name. The group ID identifies the group of the user who created the process.
Syntax : ps -G group_name ps --Group group_name Example : [root@rhel7 ~]# ps -G root
- View by group id :
Syntax : ps -g group_id ps -group group_id Example : [root@rhel7 ~]# ps -g 1 PID TTY TIME CMD 1 ? 00:00:13 systemd
- View process by process ID.
Syntax : ps p process_id ps -p process_id ps --pid process_id Example : [root@rhel7 ~]# ps p 27223 PID TTY STAT TIME COMMAND 27223 ? Ss 0:01 sshd: root@pts/2 [root@rhel7 ~]# ps -p 27223 PID TTY TIME CMD 27223 ? 00:00:01 sshd [root@rhel7 ~]# ps --pid 27223 PID TTY TIME CMD 27223 ? 00:00:01 sshd
You can view multiple processes by specifying multiple process IDs separated by blank or comma –
[root@rhel7 ~]# ps -p 1 904 27223 PID TTY STAT TIME COMMAND 1 ? Ss 0:13 /usr/lib/systemd/systemd --switched-root --system --d 904 tty1 Ssl+ 1:02 /usr/bin/X -core -noreset :0 -seat seat0 -auth /var/r 27223 ? Ss 0:01 sshd: root@pts/2
Here, we mentioned three process IDs – 1, 904 and 27223 which are separated by blank.
- Select by parent process ID. By using this command we can view all the processes owned by parent process except the parent process.
[root@rhel7 ~]# ps -p 766 PID TTY TIME CMD 766 ? 00:00:06 NetworkManager [root@rhel7 ~]# ps --ppid 766 PID TTY TIME CMD 19805 ? 00:00:00 dhclient
In above example process ID 766 is assigned to NetworkManager and this is the parent process for dhclient with process ID 19805.
- View all the processes belongs to any session ID.
Syntax : ps -s session_id ps --sid session_id Example : [root@rhel7 ~]# ps -s 1248 PID TTY TIME CMD 1248 ? 00:00:00 dbus-daemon 1276 ? 00:00:00 dconf-service 1302 ? 00:00:00 gvfsd 1310 ? 00:00:00 gvfsd-fuse 1369 ? 00:00:00 gvfs-udisks2-vo 1400 ? 00:00:00 gvfsd-trash 1418 ? 00:00:00 gvfs-mtp-volume 1432 ? 00:00:00 gvfs-gphoto2-vo 1437 ? 00:00:00 gvfs-afc-volume 1447 ? 00:00:00 wnck-applet 1453 ? 00:00:00 notification-ar 1454 ? 00:00:02 clock-applet
- Select by tty. This selects the processes associated with the mentioned tty :
Syntax : ps t tty ps -t tty ps --tty tty Example : [root@rhel7 ~]# ps -t pts/0 PID TTY TIME CMD 31199 pts/0 00:00:00 bash 31275 pts/0 00:00:00 man 31280 pts/0 00:00:00 less
- Select by effective user ID or name.
ps U user_name/ID
ps -U user_name/ID
ps -u user_name/ID
ps –User user_name/ID
ps –user user_name/ID
- Use -f to view full-format listing.
[tux@rhel7 ~]$ ps -af tux 17327 17326 0 12:42 pts/0 00:00:00 -bash tux 17918 17327 0 12:50 pts/0 00:00:00 ps -af
- Use -F to view Extra full format.
[tux@rhel7 ~]$ ps -F UID PID PPID C SZ RSS PSR STIME TTY TIME CMD tux 17327 17326 0 28848 2040 0 12:42 pts/0 00:00:00 -bash tux 17942 17327 0 37766 1784 0 12:50 pts/0 00:00:00 ps -F
- To view process according to user-defined format.
Syntax : [root@rhel7 ~]# ps --formate column_name [root@rhel7 ~]# ps -o column_name [root@rhel7 ~]# ps o column_name Example : [root@rhel7 ~]# ps -aN --format cmd,pid,user,ppid CMD PID USER PPID /usr/lib/systemd/systemd -- 1 root 0 [kthreadd] 2 root 0 [ksoftirqd/0] 3 root 2 [kworker/0:0H] 5 root 2 [migration/0] 7 root 2 [rcu_bh] 8 root 2 [rcu_sched] 9 root 2 [watchdog/0] 10 root 2
In this example I wish to see command, process ID, username and parent process ID, so I pass the arguments cmd, pid, user and ppid respectively.
- View in BSD job control format :
[root@rhel7 ~]# ps -j PID PGID SID TTY TIME CMD 16373 16373 16373 pts/0 00:00:00 bash 19734 19734 16373 pts/0 00:00:00 ps
- Display BSD long format :
[root@rhel7 ~]# ps l F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND 4 0 904 826 20 0 306560 51456 ep_pol Ssl+ tty1 1:32 /usr/bin/X -core -noreset :0 -seat seat0 -auth /var/run/lightdm/root/:0 -noli 4 0 11692 11680 20 0 115524 2132 do_wai Ss pts/2 0:00 -bash
- Add a column of security data.
[root@rhel7 ~]# ps -aM LABEL PID TTY TIME CMD unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 19534 pts/2 00:00:00 man unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 19543 pts/2 00:00:00 less unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 20469 pts/0 00:00:00 ps
- View command with signal format.
[root@rhel7 ~]# ps s 766
- Display user-oriented format
[root@rhel7 ~]# ps u 1 USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.6 128168 6844 ? Ss Apr08 0:16 /usr/lib/systemd/systemd --switched-root --system --deserialize 21
- Display virtual memory format
[root@rhel7 ~]# ps v 1 PID TTY STAT TIME MAJFL TRS DRS RSS %MEM COMMAND 1 ? Ss 0:16 62 1317 126850 6844 0.6 /usr/lib/systemd/systemd --switched-root --system --deserialize 21
- If you want to see environment of any command. Then use option **e** –
[root@rhel7 ~]# ps ev 766 PID TTY STAT TIME MAJFL TRS DRS RSS %MEM COMMAND 766 ? Ssl 0:08 47 2441 545694 10448 1.0 /usr/sbin/NetworkManager --no-daemon LANG=en_US.UTF-8 PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin
- View processes using highest memory.
ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem
12 – print a process tree
[root@rhel7 ~]# ps --forest -C sshd PID TTY TIME CMD 797 ? 00:00:00 sshd 11680 ? 00:00:03 \_ sshd 16361 ? 00:00:02 \_ sshd
- List all threads for a particular process. Use either the -T or -L option to display threads of a process.
[root@rhel7 ~]# ps -C sshd -L PID LWP TTY TIME CMD 797 797 ? 00:00:00 sshd 11680 11680 ? 00:00:03 sshd 16361 16361 ? 00:00:02 sshd
Note – For the explanation of different column contents refer man page.
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Output Format control
These options are used to choose the information displayed by ps. There are multiple options to control output format. These option can be combined with any other options like e, u, p, G, g etc, depends on our need.
Reference : Man page
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