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Ntakwetet
Asked: 2019-11-25 12:52:15 +0800 CST

How to run a script at boot and then every 30 minutes

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I have an Ubuntu Server machine in which I need to run a Python script:

  • at boot and then every 30 minutes
  • with root permission
  • without logging in

I searched on the internet and I found out that I should use sudo crontab -e to edit my cron settings and add a line like this one:

 30 * * * * python3 /myScriptPath/myScriptName.py

What I couldn't find is how to tell cron that my script must be run at boot and then every 30 minutes and not every hour at "hh:30" time.

Also, where should I store my script?

scripts server automation cron

1 Answers

  1. Best Answer

    Write a control file and place it in /etc/cron.d/myscriptrun

    SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
@reboot   root    /usr/local/bin/myscript.sh

    Do not make this file executable. It is a control file not a script.

    Write a bash script and place it in /usr/local/bin/myscript.sh

    #!/bin/bash

while true ; do

    python3 /myScriptPath/myScriptName.py &
    sleep 30m

done

    Make it executable chmod a+x /etc/cron.d/bashscript.

    The & starts the job in the background so the script will sleep for exactly 30 minutes. You can remove the & and that changes the script to sleep 30 minutes after the job ends. Meaning jobs no longer start 30 minutes apart.

    Cron runs your job

    You don't need to start the script, cron does that automatically at boot time. To monitor status use:

    $ systemctl status cron*
● cron.service - Regular background program processing daemon
   Loaded: loaded (/lib/systemd/system/cron.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2019-11-12 06:01:27 MST; 1 weeks 6 days ago
     Docs: man:cron(8)
 Main PID: 1115 (cron)
   CGroup: /system.slice/cron.service
           ├─1115 /usr/sbin/cron -f
           ├─1132 /usr/sbin/CRON -f
           ├─1138 /bin/sh -c    /usr/local/bin/eyesome.sh
           ├─1142 /bin/bash /usr/local/bin/eyesome.sh
           ├─1160 /bin/bash /usr/local/bin/eyesome-dbus.sh
           ├─1168 dbus-monitor --system type=method_call, interface=org.freedesktop.ColorManag
           ├─1169 /bin/bash /usr/local/bin/eyesome-dbus.sh
           └─6575 sleep 57207

    Your display will have cron at the top and sleep at the bottom but will not have eyesome stuff in the middle, unless you are using that sunrise/sunset multiple monitor brightness/gamma transitioning software.

    To see when your python job runs at it's next 30 minute interval run an inquiry on the process ID of the sleep command (which is 6575 in the example above):

    $ remaining_sleep_time 6575
55923

$ echo $((55923/60))
932

    The time remaining is 55923 seconds divided by 60 seconds in a minute = 932 minutes before the job wakes up. To get a copy of remaining_sleep_time function see:

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