Scheduling Jobs Using at Command in Linux

By Rahul3 Mins ReadUpdated:

While working with Linux systems we preferred crontab for scheduling jobs generally. There are another utility at command is very useful for scheduling one time tasks. It reads commands from standard input or script/file which can be executed later once. But we can’t use at command for any recurring tasks. For recurring tasks use Linux crontab.

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At command can be useful for shutdown system at the specified time, Taking a one-time backup, sending an email as a reminder at the specified time, etc. This article will help you to understand the working of at command with useful examples.

Commands used with at:

  • at : execute commands at specified time.
  • atq : lists the pending jobs of users.
  • atrm : delete jobs by their job number.

1. Schedule a Job Using ‘at’ Command

The below example will schedule the backup.sh command to be executed at 9:00AM once.

at 9:00 AM 
 sh backup.sh 
 ^d 

Output

job 3 at 2013-03-23 09:00

Use ^d to exit from at prompt.
You can also use the following option to schedule a job. The below command will run the backup.sh script at 9:00 in the morning.

echo "sh backup.sh" | at 9:00 AM

2. List the scheduled jobs using atq

When we list jobs by root account using atq, it shows all user’s jobs in the result. But if we execute it from a non-root account, it will show only that user’s jobs.

atq

Output

3       2013-03-23 09:00 a root
5       2013-03-23 10:00 a rahul
1       2013-03-23 12:00 a root

Fields description:
First filed: job id
Second filed: Job execution date
third filed: Job execution time
Last field: User name, under which job is scheduled.

3. Remove scheduled job using atrm

You can remove any job using atrm with their job id.

atrm 3
atq

Output

5       2013-03-23 10:00 a rahul
1       2013-03-23 12:00 a root

4. Check the content of scheduled at job

The atq command only shows the list of jobs but if you want to check what script/commands are scheduled with that task, the below example will help you.

at -c 5

In the above example, 5 is the job id.

Examples of at Command:

  1. Schedule task at coming 10:00 AM.
    at 10:00 AM
  2. Schedule task at 10:00 AM on coming Sunday.
    at 10:00 AM Sun
  3. Schedule task at 10:00 AM on coming 25’th July.
    at 10:00 AM July 25
  4. Schedule task at 10:00 AM on coming 22’nd June 2015.
    at 10:00 AM 6/22/2015 
at 10:00 AM 6.22.2015
  5. Schedule task at 10:00 AM on the same date as next month.
    at 10:00 AM next month
  6. Schedule task at 10:00 AM tomorrow.
    at 10:00 AM tomorrow
  7. Schedule task at 10:00 AM tomorrow.
    at 10:00 AM tomorrow
  8. Schedule task to execute just after 1 hour.
    at now + 1 hour
  9. Schedule task to execute just after 30 minutes.
    at now + 30 minutes
  10. Schedule tasks to execute just after 1 and 2 weeks.
    at now + 1 week 
at now + 2 weeks
  11. Schedule tasks to execute just after 1 and 2 years.
    at now + 1 year 
<at now + 2 years
  12. Schedule tasks to execute at midnight.
    at midnight

    The above job will execute at 12:00 AM

Thanks for reading this article, I hope you will understand how to use the ‘at’ command in Linux.

at scheduling task
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29 Comments

  3. leandro on

    How can we schedule a gtk “graphical” job, for example a simple yad message?
    yad –title “Warning” –text “Alarm now, attention” –on-top –borders=25

    In my tests, no display is shown at a specified time.

    Reply
  4. Alexey on

    How is it better to schedule installation of upgrades?
    For some reason tasks don’t execute. I tried something like: sudo apt-get upgrade -y | at 21:00

    Reply
  7. Tharun on

    please tell me that i want to run a corntab command in every last day of the month.
    i am thinking but in some its 30 days and 31 in some and 28 and 29 like that.

    Reply
    • Rahul on

      Hi Tharun,

      You can try cron like this:

      59 23 28-31 * * [ "$(date +%d -d tomorrow)" = "01" ] && /root/script.sh

      here [ “$(date +%d -d tomorrow)” = “01” ] will retrun true if tomorrow is the first day of next month.

      Reply
  8. bartek on

    I’m using at to run mplayer and stream some radio station, when i want to stop mplayer and use atrm command it doesn’t work. i got only ” Warning: deleting running job” . job vanishes from the atq list, but it still streams music.

    Reply
  9. NISHANT SACHDEVA on

    HI, I am experiencing an issue. When i am using the format:
    command | at time

    It is not executing the command that I am providing.
    Please tell how to get past it.

    Reply
  10. Sergey on

    Great article Rahul!
    I just wanted to extend it a bit with some useful additions.
    1) You can use -f option to point “at” to the script you need to run:
    at -f /path/to/the/script time_spec
    2) One can use “at” to start a process in background without nohup, etc. As easy as
    at -f /a/command now
    or
    echo “/a/command” | at now
    3) You can use “at” to run a command repeatedly, but unlike cron you can use “at” to run commands with some period between runs, for example after 3 minutes after previous run was completed. This allow you to avoid various checks preventing next run to start before previous is finished.
    Moreover you can define this period as random value. Examples:
    The script (lets name it /home/user1/at_run.sh):
    ————————————-
    #!/bin/bash
    /the/command/you/need
    # fixed period between runs
    period=3
    # or random period. RANDOM is a bash’s random number from 0 to 32767
    period=$[ ($RANDOM % 20) + 15 ]
    at -f /home/user1/at_run.sh now + $period minutes
    ————————————-
    run /home/user1/at_run.sh and all next runs will be scheduled automatically, so your /the/command/you/need will run repeatedly forever. Sure, you can break the next run with atq/atrm.

    Reply
    • Francois Scheurer on

      Thx Rahul and Sergey.

      @Sergey, in your last point you are basically using a wrapper with a random pause and re-scheduling of the at job.

      I think this is also achievable with cron, without the “various checks preventing next run to start before previous is finished”.
      You can just replace the last line of your script with this:

      sleep $(($period * 60)) && exec /home/user1/at_run.sh

      Then set a crontab for /home/user1/at_run.sh .
      Note: the ‘exec’ bash builtin will prevent calling bash recursively (nested bash’s) and spare memory.
      You will need to kill the process to end it.

      If the job is not supposed to stay permanently (boot safe), I would prefer to use an interactive bash inside a ‘screen’ command and just do a loop:

      while : ; do
      /the/command/you/need
      sleep 60
      done

      So you can follow in “live” the output of the script.

      Reply
  11. archie on

    hello!
    i am running centos. when i submit an at nothing happens. i can call it up using “atq #”, however, it doesn’t execute?
    thanks for the help!!!

    Reply
  13. shitanshu on

    Hi,

    I need to run a script at particular time-stamp which internally calls one more script.
    But I am getting an error :

    at `./radConnect.sh` 09:00
    sh: netstat: command not found
    sh: /sbin/ifconfig: No such file or directory
    Radskman rc:[0] [Request successfully completed]
    syntax error. Last token seen: h
    Garbled time

    Reply
      • shitanshu on

        Hi Rahul,
        Thanks for the quick response, the use case which I am trying is a bit different.
        I have created some containers using a script and a script internally calls another one which needs to run at a particular timestamp. So the command prompt for giving the script won’t be visible. So is there any alternative to it. Or can we do it using crontab?

        Reply
  14. maillot psg 2013 on

    Wow that was unusual. I just wrote an incredibly long comment but after I clicked submit my comment didn’t appear. Grrrr… well I’m not writing all that over again. Anyway, just wanted to say fantastic blog!

    Reply

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