When exiting the shell of a Linux System, all running processes are usually terminated or hang up. So what do you do If you still want to keep the processes running even exiting the shell/terminal? This is where the nohup command comes in.
Nohup Command
Nohup, short for no hang up is a command in Linux systems that keep processes running even after exiting the shell or terminal.
Nohup prevents the processes or jobs from receiving the SIGHUP (Signal Hang UP) signal. This is a signal that is sent to a process upon closing or exiting the terminal. In this guide, we take a look at the nohup command and demonstrate how it can be used.
Nohup Command Syntax
Nohup command syntax is as follows;
nohup command arguments
OR
nohup options
Let’s see how the command comes into play
Checking the version of Nohup
You can begin by checking the version of Nohup using the syntax below
nohup --version
Output
Starting a process using Nohup
If you want to keep your processes/jobs running, precede the command with nohup
as shown below. The jobs will still continue running in the shell and will not get killed upon exiting the shell or terminal.
nohup ./hello.sh
Output
From the output above, the output of the command has been saved to nohup.out
to verify this run,
cat nohup.out
Output
Additionally, you can opt to redirect the output to a different file as shown
nohup ./hello.sh > output.txt
Once again, to view the file run
cat output.txt
Output
To redirect to a file and to standard error and output use the > filename 2>&1
attribute as shown
nohup ./hello.sh > myoutput.txt >2&1
Output
Starting a process in the background using Nohup
To start a process in the background use the &
symbol at the end of the command. In this example, we are pinging google.com and sending it to the background.
nohup ping google.com &
Output
To check the process when resuming the shell use the pgrep
command as shown
pgrep -a ping
Output
If you want to stop or kill the running process, use the kill
command followed by the process ID as shown
kill 2565
Output
Summary
- All processes that are run using the nohup command will ignore the SIGHUP signal even upon exiting the shell.
- Once a job is started or executed using the nohup command, stdin will not be available to the user.
- By default, the
nohup.out
is used as the default file for stdout and stderr.
Hi. Thanks for the nice tips. I am a newbie in this field and I have a simple question. well, I am using nohup in my work in the background. well. I am facing a problem which is. once I submit the job it working well in the background. no issue. but I have 50+ commands to run. so it is creating a long queue. now the problem is that each job take some time to finish and because of that a long-waited queue got cancel automatically. is there any way to keep it in the queue or prolonged the queuing time or another way by which PID keep activate itself until its turn come for execution? love to hear from your expertise. Thanks
Why not put your commands in a script and nohup the script 🙂
How do I use nohup to run script. Ànd how can I see/monitor the logs
great for tcpdump :
nohup sudo tcpdump -i any -nn -w /var/tmp/file.pcap -C 100 -W 50 “src x.x.x.x and dst y.y.y.y” &
•to find the process that u created :
– pgrep -a tcpdump
– ps aux | grep
then : sudo kill
When you run this command normally, does it produce any output as you are redirecting the output in a file.
how do i run nohup for this type of cmd
cat out.csv | cut -d “,” -f3,4 | sed ‘s/,/\t/g’ | sort -n -k 2 > out.txt
nohup cat out.csv | cut -d “,” -f3,4 | sed ‘s/,/\t/g’ | sort -n -k 2 > out.txt & – doesn’t work
dinesh, try
nohup bash -c “cat out.csv | cut -d “,” -f3,4 | sed ‘s/,/\t/g’ | sort -n -k 2” >out.txt &
this should work