What's a simple way to run a command, say, 8 hours from now? I can think of this way:

nohup bash -c "sleep 28800 ; ./mycommand.sh" &

Is there a more "proper" way?


6 Answers 6


You can use the at command. The at execute commands at a later time. The at utility shall read commands from standard input and group them together as an at-job, to be executed at a later time.

Usually, at is installed by default in Ubuntu, but if your release doesn't include it, install via:

sudo apt-get install at

For more information, options, examples, and others, see the manpage in man 1 at.

Example of a relative time specification (note the space between + and the duration):

at now + 8 hours -f ~/myscript.sh

You can also use convenient shorthands, like tomorrow or noon, as in

echo "tweet fore" | at teatime 

Note: This will run the command to the left of the pipe immediately - and its output (which is piped to at) will be run by at at the scheduled time. So, the above command schedules tweet fore to be run at teatime.

The example also demonstrates how you can pipe actions into at. at -c is the way you can examine scheduled actions, which you can conveniently list with their number, as with:

at -c 3
  • 7
    In addition, there is at 8:00 to run the command at an absolute time, and batch for "when it looks like the computer is idle" Aug 30, 2013 at 18:09
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    In case anyone was wondering, teatime is at 4pm. For some reasons it's not mentioned in manpages.ubuntu.com/manpages/raring/man1/at.1posix.html but it is in man at and here manpages.ubuntu.com/manpages/raring/en/man1/at.1.html.
    – Dan
    Sep 6, 2013 at 7:53
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    Maybe we can mention that "at" utility is not installed by default and if anyone else want to get it simply install the "at" package? Edit: Anyway, i simply edited the answer (also fixed the manpage link). Feb 12, 2014 at 10:11
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    One nuisance I've discovered with at is its lowest resolution is 1 minute. You can schedule now or +1 minute but nothing between. Can be a bit annoying for trying to just fork a job. Aug 7, 2014 at 14:07
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    about the whole piping-into-at running now instead of later issue, echo "/command/to/run" | at teatime produces the desired outcome
    – rmanna
    Jan 24, 2018 at 10:40

Yes, you can set a cron job.

For example if now the time is 14:39:00 and today is friday, 30 august, you can add the following cron job (to be executed after 8 hours) in your crontab file using crontab -e command:

39 22 30 8 5  /path/to/mycommand.sh

More about:

  • 4
    Ok, yes, I should have mentioned I know about Cron jobs. This is even messier because then it sits around in the crontab indefinitely, right? Aug 30, 2013 at 12:55
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    @RaduRădeanu: with cron, careful that it could fire again in a few years (when there is another 30th of August occuring on a friday) ... Aug 30, 2013 at 13:12
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    This is a clever hack. However 'at' is a much better way. What would happen if the computer was turned off at 14:39?
    – emory
    Aug 30, 2013 at 14:47
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    Err that's still not my point. My point is that the text you entered will (I think) literally still be sitting in your crontab after the event, creating another cleanup task for you. Sep 4, 2013 at 1:20
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    @SteveBennett Yes, you are correct. The command will remain in your crontab until you remove it. A year later, when you have forgotten who put it there and why, you will be left scratching your head wondering what to do with the command. Sep 4, 2013 at 16:05

Use the Gnome-based GUI for cron, at, and the like:

The introduction of the CronHowto suggests using the gnome-schedule gui, which is much nicer than typing all the garbage into the terminal (esp. for "average" Ubuntu users who are not "power" *nix/bsd users.)

Run it by using the Unity Dash (or other applications menu) to look for Scheduled Tasks or running gnome-schedule.

On Gnome-based Ubuntu systems Gnome Scheduled tasks tool (from the gnome-schedule package) in Applications --> System Tools provides a graphical interface with prompting for using Cron. The project website is at http://gnome-schedule.sourceforge.net/; the software is installable from the Software Center or by typing

sudo apt-get install gnome-schedule

in a terminal.

Using gnome-schedule, for a script in your home directory, a new "at" command would be set up using this type of window:

enter image description here

  • 1
    gnome-schedule doesn't seem to exist for Ubuntu 21.04
    – Prof.Chaos
    Aug 27, 2021 at 2:49

Check the output of date in a loop. This is a quick and dirty way to do this, like if you can't use at, cron, or other tools.

Say you want your script to run at noon:

until [[ $(date +%H:%M) == 12:00 ]]; do
    sleep 30

Say you want it to run tomorrow at noon (today is Nov 24 for me):

until [[ $(date +%d_%H:%M) == "25_12:00" ]]; do 
    sleep 30

Previously, this answer recommended regex, which has some pitfalls, like a lot of special characters. As well it recommended matching against the whole date string, which is more error-prone since it's locale-dependent. For example, I use some French locale formats since I live in Quebec, so if I forget about that and write until [[ $(date) == "25 12:00" ]], it will never match because the French ordering is "day month year, time" instead of the English "month day time year".

  • 13
    To the two people who've upvoted this answer, please use at, cron, or any other real scheduler application. Task scheduling is hard, and not a wheel you should reinvent.
    – dimo414
    Jan 20, 2017 at 8:39
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    @dimo414 What's wrong with my method?
    – wjandrea
    Jan 20, 2017 at 17:20
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    At a minimum, it's busy-waiting, which is wasteful. Worse, it's not guaranteed to be correct; it's perfectly possible (if unlikely) for the conditional to be missed. Basing your scheduler on regular expressions is also highly error-prone. It might work well-enough, but has no advantages over at.
    – dimo414
    Jan 20, 2017 at 17:36
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    Another reason to use at is because its jobs will survive a reboot.
    – manatwork
    Feb 28, 2017 at 10:25
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    My server doesn't have at installed and I'm a user without sudo. I think this alternative is better. @dimo414
    – yihui.dev
    Dec 8, 2018 at 6:05

If you are running bash on a mac you will run into some difficulties using the at program. In that case you can improve on your original proposed solution of,

nohup bash -c "sleep 28800 ; ./mycommand.sh" &

with this,

nohup bash -c "sleep $(echo '8 * 60 * 60' | bc) ; ./mycommand.sh" &

which is a more readable form of how long you want to wait. In this example 8 is the number of hours you want to wait before running your script mycommand.sh.

  • Why you have chosen to use bc instead of shell arithmetic expansion? i.e. nohup bash -c "sleep $((8*60*60)) ; ./mycommand.sh" &
    – diabolusss
    May 19, 2023 at 20:05

In order to install gnome-schedule on Ubuntu 21.04 you can do

$ sudo snap install gnome-schedule --edge --jailmode

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