nohup Execute Commands After You Exit From a Shell Prompt

Posted on in Categories CentOS, Debian Linux, FreeBSD, Gentoo Linux, GNU/Open source, Howto, Linux, Linux desktop, Networking, RedHat/Fedora Linux, Shell scripting, Solaris, Suse Linux, Tips, Tuning, UNIX last updated January 4, 2006

Most of the time you login into remote server via ssh. If you start a shell script or command and you exit (abort remote connection), the process / command will get killed. Sometime job or command takes a long time. If you are not sure when the job will finish, then it is better to leave job running in background. But, if you log out of the system, the job will be stopped and terminated by your shell. What do you do to keep job running in the background when process gets SIGHUP?

Say hello to nohup command

The answer is simple, use nohup command line-utility which allows to run command/process or shell script that can continue running in the background after you log out from a shell:

nohup command syntax:

The syntax is as follows
nohup command-name &
OR
nohup /path/to/command-name arg1 arg2 &

Where,

  • command-name : is name of shell script or command name. You can pass argument to command or a shell script.
  • & : nohup does not automatically put the command it runs in the background; you must do that explicitly, by ending the command line with an & symbol.

Use jobs -l command to list all jobs:
# jobs -l

nohup command examples

First, login to remote server using ssh command:
$ ssh [email protected]
OR
$ ssh [email protected]

I am going to execute a shell script called pullftp.sh:
# nohup pullftp.sh &

Type exit or press CTRL + D exit from remote server:
# exit

In this example, I am going to find all programs and scripts with setuid bit set on, enter:
# nohup find / -xdev -type f -perm +u=s -print > out.txt &

Type exit or press CTRL + D exit from remote server.
# exit

Please note that nohup does not change the scheduling priority of COMMAND; use nice command for that purpose. The syntax is:
# nohup nice -n -5 ls / > out.txt &
As you can see nohup keep processes running after you exit from a shell. Read man page of nohup(1) and nice(1) for more information. Please note that nohup is almost available on Solaris/BSD/Linux/UNIX variants.

Other options (suggested by readers)

You can use at command to queue a job for later execution. For example, you can run pullftp.sh script to queue (one minute) later execution:
$ echo "pullftp.sh" | at now + 1 minute
You can also use screen command for same. The disown shell internal command for same purpose. Here is how you can try it out:
$ pullftp.sh &
$ disown -h
$ exit

From the bash bash(1) man page:

By default, removes each JOBSPEC argument from the table of active jobs. If the -h option is given, the job is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. The -a option, when JOBSPEC is not supplied, means to remove all jobs from the job table; the -r option means to remove only running jobs.

Recommended reading

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

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42 comment

  1. Thank you. I’ve been searching for this. I knew this kind a functionality should exist. Often i had this issue when ever I’m connecting from home to my office-server.

    BR 🙂

  2. Hi everybody.

    I am working as sys admin on linux and now i want to learn a programming lanuage can anybody suggest which one i should go for. Which can help me both at admin work and with small app programs.

    regards
    anil

  3. Thanks for the reply. Yes command is in current directory but nohup log lists several complaints about not being able to find various files. Also, when executing, I was expecting to be returned to the command prompt which I was not.

  4. I just checked with my Unix admin who thinks that it does not matter whether you include the ./ in the nohup string. Also, If I hit return during the process I get my prompt back and can run a monitoring script.

  5. Hi and thanks for the reply. I am seeing error messages that files cannot be found that I know are present in a different folder (where it should be looking). That is what concerned me that I might have forced the process to look only in it’s current directory with “./”. When I get the prompt back I can ps and see the job running.

  6. I have the situation…
    I did ssh to the remote server. Run the yum -y update command without nohup!
    The updating run for a while and I want to log out off the remote server…and I want yum still run even I log out..
    How can I use ‘nohup’ without canceling my update !
    thanks for any suggestions !!

  7. Question: I started a nohup foo & . Now I want to stop it… is there a way to end the process even though I ‘nohupped’ it prior?

    The process had an error and stopped running, but I am still logged into the server even after I close my SSH terminal.

    Thanks in advance!

  8. Hi There
    My nohup keeps ending with “Cancel request sent”

    nohup Scriptfile.ksh > Scriptlog.log 2>&1 &

    this happens even when I nohup it as you can see above

    Any help would be much appreciated

  9. > Aggdata September 3, 2010
    > Hi There
    > My nohup keeps ending with “Cancel request sent”
    > nohup Scriptfile.ksh > Scriptlog.log 2>&1 &
    > this happens even when I nohup it as you can see above
    > Any help would be much appreciated
    [ sameeroak ]
    try the following:
    nohup > /dev/null 2>&1 Scriptfile.ksh > Scriptlog.log &

  10. Hi everybody.
    I have launched a set of commands with the nohup features. If i launch “top” i have 4 processes running in the background, all having the same name.
    Is there a way i can go back to the command line that launched each of the processes?
    To be correct, i have written a small bash file that launches all the programs one aftert the other.

    so what i’ve done is:

    chmod +x bash.sh
    nohup ./bash.sh >/dev/null &

    I have 4 different files, each launching a set of processes having all the same name. I need to recall only one of this bash files because i ve noticed i gave a wrong input.
    thanks for the help,

    F.

  11. Thanks, just what I needed!

    It happens often that I’m too lazy to use the GUI and so I’d simply hack in a

    $ iceweasel &>/dev/null &

    on my Debian to have an iceweasel running without giving this pointless debug output crap.
    HOWEVER, beware if you have an (l)xterm with 2 tabs, and this is the 1st tab! You might mess up this sub-terminal completely, and close it, leaving only the 2nd tab open!
    Of course, you guessed it — iceweasel will be KILLED.
    nohup can avoid that. I presume that the ‘Run’ command in LXDE dropdown menu does a nohup under the veil, too.

  12. Hello All

    Can anyone tell how to stop if I execute my command line using nohup .
    If by mistake if have input wrong command i want to exit from backround execution or nohup commad , How to do it,Kindly let me know

  13. nohup pullftp.sh &
    i m trying to execute this command but unable to execute , why ?

    please tell me the exect way to run a command
    ######################################################
    /var/root/akash # sh home.sh
    45
    70
    90
    160
    /var/root/akash # nohup home.sh>main.txt &
    /var/root/akash # cat main.txt
    nohup: can’t execute ‘home.sh’: No such file or directory
    [1]+ Done(127) nohup home.sh 1>main.txt
    #######################################################

  14. if i log into a server from home
    and use e.g.
    # nohup wget -q -c -O test_fastq.gz “http://addressexample” &
    # exit

    will the (large) download continue to the server without using my home broadband allowance?

    thanks

  15. Hi team ,
    please can anyone explain we are RHEL 7.2 for our project
    But our system monitor 19 inches how to correct the resolution,
    sometime display not coming but we can able to access remotely but not for direct graphically login ,please give me a solution .

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