Table of Contents
How to list processes by user and name in Linux? How to check if process is running by
pid? How to check process status? which command is used to kill a process?
In this tutorial we will cover all these questions and explore different commands and tools to list and manage processes in Linux and Unix.
ps command is the best tool to list down all the running processes across the server. There are a wide range of arguments which can be used with ps to list processes based in our requirement.
List all the running processes
Method-1: Using "px aux"
To list every process on the system using BSD syntax:
# ps aux
ax Lift the BSD-style "only yourself" restriction, which is imposed upon the set of all processes when some BSD-style (without "-") options are used or when the ps personality setting is BSD-like. u Display user-oriented format.
This will give you a long list of output with more details on individual process such as memory and cpu usage, status, user owner of the process and more. Following is a snippet from my terminal:
Method-2: Using "ps -ef"
The next method will list all the running process using standard syntax:
# ps -ef
-e Select all processes -f Do full-format listing.
This gives lesser information compared to
Method-3: Using "ps -ely"
We can use some more arguments with
ps to list the running processes in Linux:
# ps -ely
-e Select all processes. -l Long format -y Do not show flags; show rss in place of addr
This command will give us additional detail compared to
ps -ef such as priority and nice value of individual process.
List processes by user
To list all the processes based on user owner we can use following syntax:
ps -U USER -u USER u
-U userlist Select by real user ID (RUID) or name. It selects the processes whose real user name or ID is in the userlist list. The real user ID identifies the user who created the process, -u userlist Select by effective user ID (EUID) or name. This selects the processes whose effective user name or ID is in userlist. u Display user-oriented format.
To list the process started by user root:
~]# ps -U root -u root u
Sample output from my terminal:
To list the process started by normal user
~]# ps -U deepak -u deepak u USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND deepak 5575 0.0 0.0 280884 8508 ? S Oct20 0:05 python /opt/deepak/jboss/bin/dualprim_watch.py -a 20 -m 500 -U nds -L 500 -t 10 deepak 8995 0.0 0.0 113420 1628 ? S Oct20 0:00 /bin/sh /opt/deepak/jboss/bin/standalone.sh -b 0.0.0.0 -c standalone-full-adm.xml deepak 9208 2.9 3.6 23510668 4848336 ? Sl Oct20 50:04 /usr/lib/jvm/java-1.8.0-openjdk-188.8.131.52.b09-2.el7_8.x86_64/jre/bin/java -D[Standal
List the process tree
Method-1: Using "ps axjf" or "ps -ef --forest"
We can also use
ps command to list the running process in the tree format to understand the parent and child processes.
~]# ps axjf
~]# ps -ef --forest
Method-2: Using pstree
Although you have a better alternative to above command if you wish to see the structure of all the running process using
pstree which is part of
psmisc rpm in RHEL/CentOS distribution. This command is used to display the parent-child relationship in hierarchical format.
~]# pstree -p
-p Show PIDs. PIDs are shown as decimal numbers in parentheses after each process name
To list the process tree of process started by individual user, you can use
~]# pstree -p USERNAME
For example to show the process tree of user
~]# pstree -p deepak
You can check the man page of pstree for more list of supported options.
List thread count for individual process
We can use
-L argument to list the number of threads along with individual process. It will add a new column in the output possibly with LWP and NLWP
~]# ps -eLf
Sample output from this command:
List process with user defined format
ps will show a certain default list of columns. You can manipulate and print your own set of columns to get the required details of a process by using following syntax:
ps -eo ARUMENTS
Here, you can replace the ARGUMENTS with supported list of values from man page of ps
Example-1: Show only PID and command
To show only the list of PID and their respective commands:
~]# ps -eo pid,comm PID COMMAND 1 systemd 2 kthreadd 3 rcu_gp 4 rcu_par_gp 6 kworker/0:0H-kblockd ...
Example-2: Show memory and cpu details of each process
There are different arguments which you can use to print the memory and cpu related information of individual process, here I have consolidated a few:
~]# ps -eo pid,%mem,%cpu,rss,rsz,vsz,comm PID %MEM %CPU RSS RSZ VSZ COMMAND .... 902 0.2 0.0 14420 14420 424800 sssd 904 0.1 0.0 5220 5220 82744 avahi-daemon 905 0.4 0.0 22152 22152 1626068 polkitd 912 0.2 0.0 14640 14640 462728 ModemManager 914 0.0 0.0 2012 2012 18872 lsmd 916 0.0 0.0 2136 2136 17408 mcelog ....
Get process ID of a process
Now assuming you have a running process for which you want to get the PID so we can again use
ps in this format:
ps -C PROCESS -o pid=
Here we need to replace
PROCESS with the name of the process or command for which we want to perform the lookup of PID. For example to get the PID of
~]# ps -C rsyslogd -o pid= 1540
Similarly to get the list of PID for
~]# ps -C sshd -o pid= 999 1705 1899 2009 2011 2319 2321 2342 2344 13874 13879
Get process name using the PID
Now if the situation is reversed, i.e. you have the PID and you wish to get the process or command of the mapping PID then you can use following format:
ps -q PID -o comm=
Here, replace PID with the pid value of the process for which you have to perform lookup. Following are some examples where we get the process name using the PID value.
~]# ps -q 2009 -o comm= sshd ~]# ps -q 1 -o comm= systemd
List stopped processes
You can stop a running or hung process using ctrl+z short key. When you press this key combination, the ongoing process on the terminal will be forcefully stopped.
For example, here I had an SFTP session which was stuck so I pressed
ctrl+z to stop the process forcefully which immediately stops the process and returns to console.
~]# sftp -o Port=2222 firstname.lastname@example.org email@example.com's password: Connected to firstname.lastname@example.org. sftp> exit Interrupt ^Z + Stopped sftp -o Port=2222 email@example.com
To list all the processes which are in stopped state use
~]# jobs  Stopped sftp -o Port=2222 firstname.lastname@example.org - Stopped sftp -o Port=2222 email@example.com + Stopped sftp -o Port=2222 firstname.lastname@example.org
So currently in my server, I have 3 stopped processes. To kill a stopped process we use
kill %[JOB ID]
where JOB ID is the ID number you see with "Stopped" under square brackets.
So for example to kill the process with job ID 3 we will use:
~]# kill %3 + Stopped sftp -o Port=2222 email@example.com
Next if I check the current stopped processes then I see that the process with JOB ID 3 is marked as Exit which means it is in the verge of getting killed (almost dead)
~]# jobs  Stopped sftp -o Port=2222 firstname.lastname@example.org - Stopped sftp -o Port=2222 email@example.com + Exit 1 sftp -o Port=2222 firstname.lastname@example.org
We check the status again in few seconds and our process with JOB ID 3 is not there in the list any more and was killed successfully
]# jobs - Stopped sftp -o Port=2222 email@example.com + Stopped sftp -o Port=2222 firstname.lastname@example.org
In this tutorial we learned about listing and managing Linux processes using ps command. We also have other tools such as
htop which can list the system processes but I find ps more suitable in most scenarios. If you requirement is to watch the runtime status of process i.e. to monitor a process and it's status then top would be your best alternative as it continuously monitors the status of process and shows you latest stat for memory, cpu usage and other related values.