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Find out what processes are running in the background on Linux

How to find out what processes are running in the background

1. You can use the ps command to list all background process in Linux. Other Linux commands to obtain what processes are running in the background on Linux.
2. top command – Display your Linux server’s resource usage and see the processes that are eating up most system resources such as memory, CPU, disk and more.
3. htop command – Just like a top command but with an improved user interface.

Let us see both traditional command and modern commands examples that one can use to manage running processes in Linux.

How can I run a Linux process in the background?

To run your process or command/shell script in the background, include an & (an ampersand) at the end of the command/shell script you use to run the job. For example:
command &
/path/to/script &
sleep 10000 &

List your background processes

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To stop the foreground process press CTRL + z . One can refers to the background process or stopped process by number. For example, vim is stopped and has 1 as number, so run the bg command to restart a stopped background process:
bg %n
bg %1
One can bring a background process to the foreground such as sleep command using the fg command:
fg %n
fg %2
Finally, kill a running process named “sleep 10000” using the kill command:
kill %n
kill %2

Linux background processes list command

Open the terminal application and issue the following ps command command to show all running process on the system including those running in the background:
$ sudo ps -aux | less
OR
# ps aux | more

List all running processes on Linux using ps command

Understanding ps command outputs

The first column shows the user name who started the foreground or background processes on Linux system. For example, the daemon user started the atd process. The process name itself displayed in the last column. The STAT coloum gives us the state of a Linux process:

Process STATE code	Description
D	uninterruptible sleep (usually IO)
I	Idle kernel thread
R	running or runnable (on run queue)
S	interruptible sleep (waiting for an event to complete)
T	stopped by job control signal
t	stopped by debugger during the tracing
W	paging (not valid since the 2.6.xx kernel)
X	dead (should never be seen)
Z	defunct (“zombie”) process, terminated but not reaped by its parent

Typically process in “interruptible sleep” are running in the background and shows a “ S ” on processes STAT column. The interruptible sleep means the process can be terminated or killed with the help of kill command. On the other hand, processes in a “D” or uninterruptible sleep state are usually waiting on I/O. Therefore, you cannot kill “D” state processes as they are uninterruptible. Additional characters may be displayed as follows too:

Process STATE code	Description
	high-priority (not nice to other users)
N	low-priority (nice to other users)
L	has pages locked into memory (for real-time and custom IO)
s	is a session leader
l	is multi-threaded (using CLONE_THREAD, like NPTL pthreads do)
+	is in the foreground process group

Is my Linux process running in the foreground or background?

Based upon the above tables, one can determine if Linux process in background or foreground or running and so on.

Command/ Process	ps STATE code	Foreground or Background?
/sbin/init	Ss	Background process (interruptible sleep and a session leader)
/usr/sbin/rsyslogd -n	Ssl	Background process (interruptible sleep+a session leader and multi-threaded app)
/sbin/agetty —noclear	Ss+	Background process (interruptible sleep and a session leader and is in foreground group)
ps aux	R+	Running foreground process

Use the following command to list Linux processes along with pid, user name, stat as follows:
ps -eo pid,user,stat,comm
You can combine ps with grep command command as follows:
ps -eo pid,user,stat,comm | grep nginx

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How to check running process in Linux using command line

I am a new system administrator for the Linux operating system. How do I check running process in Linux using the command line option?

Tutorial details
Difficulty level	Easy
Root privileges	Yes
Requirements	Linux terminal
Est. reading time	4 mintues

One can use the Linux command line or terminal app to display a running process, change their priorities level, delete process and more. This page shows how to use various commands to list, kill and manage process on Linux.

Check running process in Linux

The procedure to monitor the running process in Linux using the command line is as follows:

1. Open the terminal window on Linux
2. For remote Linux server use the ssh command for log in purpose
3. Type the ps aux command to see all running process in Linux
4. Alternatively, you can issue the top command or htop command to view running process in Linux

Let us see some example and usage in details.

Please note that vivek@nixcraft:

$ is my shell prompt. You need to type commands after the $ prompt.

How to manage processes from the Linux terminal

The ps command is a traditional Linux command to lists running processes. The following command shows all processes running on your Linux based server or system:
vivek@nixcraft:

$ ps -aux
vivek@nixcraft:

1. root – User name
2. 1 – PID (Linux process ID)
3. 19:10 – Process start time
4. /sbin/init splash – Actual process or command

There may be too many processes. Hence, it uses the following less command/more command as pipe to display process one screen at a time:
vivek@nixcraft:

$ ps -aux | more
vivek@nixcraft:

$ sudo ps -aux | less
Press q to exit from above Linux pagers. You can search for a particular Linux process using grep command/egrep command:
vivek@nixcraft:

$ ps aux | grep firefox
vivek@nixcraft:

$ sudo ps aux | grep vim
vivek@nixcraft:

$ sudo ps -aux | egrep ‘sshd|openvpn|nginx’

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Linux pgrep command

Many variants of Linux comes with the pgrep command to search/find process. The syntax is:
vivek@nixcraft:

$ sudo pgrep sshd
vivek@nixcraft:

$ pgrep vim
vivek@nixcraft:

$ pgrep firefox
vivek@nixcraft:

Linux top command

The top command is another highly recommended method to see your Linux servers resource usage. One can see a list of top process that using the most memory or CPU or disk.
vivek@nixcraft:

$ sudo top
vivek@nixcraft:

Linux htop command to check running process in Linux

The htop command is an interactive process viewer and recommended method for Linux users. One can see a list of top process that using the most memory or CPU or disk and more:
vivek@nixcraft:

$ sudo htop
vivek@nixcraft:

Linux kill command

Want to kill a process? Try kill command. The syntax is:
vivek@nixcraft:

$ kill pid
vivek@nixcraft:

$ kill -signal pid
Find PID using ps, pgrep or top commands. Say you want to kill a PID # 16750, run:
vivek@nixcraft:

$ kill 16750
For some reason if the process can not be killed, try forceful killing:
vivek@nixcraft:

$ kill -9 16750
OR
vivek@nixcraft:

$ kill -KILL 16750

Linux pkill command

If you wish to kill a process by name, try pkill command. The syntax is:
vivek@nixcraft:

$ pkill processName
vivek@nixcraft:

$ pkill vim
vivek@nixcraft:

$ pkill firefox
vivek@nixcraft:

$ pkill -9 emacs
vivek@nixcraft:

$ sudo pkill -KILL php7-fpm

Linux killall command

The killall command kills processes by name, as opposed to the selection by PID as done by kill command:
vivek@nixcraft:

$ killall vim
vivek@nixcraft:

$ killall -9 emacs

Linux nice and renice command

The primary purpose of the nice command is to run a process/command at a lower or higher priority. Use the renice command to alter the nice value of one or more running Linux processes. The nice value can range from -20 to 19, with 19 being the lowest priority. Say, you want to compile software on a busy Linux server. You can set a very low priority, enter:
vivek@nixcraft:

$ nice -n 13 cc -c *.c &
Set a very high priority for a kernel update. Before rebooting Linux server, run:

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How do I see what packages are installed on Ubuntu Linux?

I am a new Ubuntu Linux server user. My server hosted at Google cloud VM. How do I see what packages are installed on Ubuntu Linux?

Introduction: Ubuntu Linux is an open source operating system based upon the Linux kernel and GNU command line utilities. Ubuntu Linux is extremely popular among new Linux users as well as developers all around the globe. This page shows how to list all installed packages with apt command or apt-get command on Ubuntu Linux.

Tutorial details
Difficulty level	Easy
Root privileges	Yes
Requirements	Debian or Ubuntu Linux
Est. reading time	5 minutes

You need to use the apt or apt-get or dpkg command to list all installed packages on an Ubuntu Linux server from the bash shell prompt.

How do I see what packages are installed on Ubuntu Linux?

The procedure to list what packages are installed on Ubuntu:

1. Open the terminal application or log in to the remote server using ssh (e.g. ssh user @ sever-name )
2. Run command apt list —installed to list all installed packages on Ubuntu
3. To display a list of packages satisfying certain criteria such as show matching apache2 packages, run apt list apache

Let us see some examples about how to list installed packages on Ubuntu and Debian Linux operating systems.

apt list installed packages

Let us list all software packages on Ubuntu Linux available for us:
$ apt list

You might want to use the grep command/egrep command to filter out:
$ apt list | grep nginx
OR
$ apt list | more
However, you may see message on screen that read as follows:

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

To avoid this message use the dpkg command as follows:
$ dpkg —list | grep nginx
$ dpkg —list | more

List all installed packages only

The apt command displays both installed and packages available to install. What if you want to list currently installed software only? Fear not, pass the option to the apt command:
$ apt list —installed

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How to list or find out if a specific package installed or not

Run package policy as follows:
$ apt list -a pkgNameHere
Is sudo package installed?
$ apt list -a sudo
Is sudo package mariadb-server?
$ apt list -a mariadb-server

Ubuntu list installed packages

It is also possible to list installed packages matching given pattern. The syntax is:
dpkg -l pattern
dpkg —list pattern
apt list pattern
apt list —installed pattern
For example:
dpkg —list ‘x*’
Sample outputs:

• ii – Indicates that package named xauth installed.
• un – Indicates that package not installed or in Unknown status.

Listing installed packages sorted by installation date and time

There is no simple command, but we can use the combination of zgrep and other commands as follows. Let us count it:

Total installed packages on nixcraft-wks01 : 6433
List them:
zgrep » installed » /var/log/dpkg.log*

Please note that zgrep will search possibly compressed files for a regular expression as those log files are compressed by system. Hence, we need to use various z commands on Linux. See “How to find out when Debian or Ubuntu package installed or updated” for more info.

Conclusion

You learned how to list both installed and uninstalled packages on an Ubuntu Linux server or desktop using the CLI method. See the following man pages using the man command:
man apt
man apt-get
man dpkg

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