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I would like to schedule a restart of my Ubuntu every 30 minutes. Is there any command or a graphical way to do it?

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I am just curious: what may be the purpose of restarting every 30 minutes? –  Rafał Cieślak Jan 16 '13 at 13:29
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4 Answers 4

The best way to do this will depend on why you want Ubuntu to restart every half hour.

So I recommend editing your question to explain why you wish to do this.

Rebooting every 30 minutes, and warning users before each reboot:

Assuming people might be using the machine, either locally or remotely, it's best to avoid restarting Ubuntu from under them without any warning. Therefore, rather than scheduling the reboot command, I recommend scheduling the shutdown command so it warns the user.

To schedule a shutdown every half hour with a warning 5 minutes before, add this to /etc/crontab:

#minute hour    mday    month   wday    user    command
*/30    *       *       *       *       root    shutdown -r +5

You don't actually have to add the fist line, which is a comment. I've included it for clarity--something like it is there already.

  • This will schedule the system to go down for reboot (-r) five minutes after (+5) the command runs. It runs every at every half hour mark (*/30). See man cron and man 5 crontab.
  • Change +5 to something else to change how long users have after being warned of reboots.
  • 0,30 under minute will also work, if you prefer that. (Similarly, if it were every 20 minutes, you could write */20 or 0,20,40.)
  • Make sure /sbin is in the PATH variable specified near the top of /etc/crontab. Otherwise, shutdown (under command) will have to be invoked as /sbin/shutdown.

The command will always run on the half-hour mark, if the machine is up and running at that time. This will cause the shutdowns to be announced every half hour and performed at 5 minutes and 35 minutes past the hour.

  • One benefit here is that an administrator can cancel the just-announced shutdown with sudo shutdown -c.
  • If the computer is down during the specific times when the scheduled command is to be run, it will not run. If that's not adequate to your needs, you'll have to schedule your reboots differently. (This is not specific to the use of shutdown but would apply equally if you were scheduling reboot.) In that case, please edit your question to explain your specific needs. (I'd recommend anacron for this, but your time intervals are far too short.)

Making it easier for administrators to prevent automatic reboots from happening at all:

You might want to set this up so that it's easy for an administrator to suspend all automatically scheduled reboots:

#minute hour    mday    month   wday    user    command
*/30    *       *       *       *       root    [ -e /etc/noautoreboot ] || shutdown -r +5

This schedules reboots the same way--every half hour, with five minutes warning--except that it will not schedule a reboot if a file called noautoreboot exists in /etc.

  • This control file can be created by an administrator with:

    sudo touch /etc/noautoreboot
    
  • It can be deleted with:

    sudo rm /etc/noautoreboot
    
  • Note that it's whether or not the file exists, not what it contains, that matters.

  • If the reboot is scheduled and users are warned, then the file is created, the (immediately upcoming) reboot will still occur.

  • How does this work? It uses a short-circuit-evaluated or operator (||) as shorthand for:

    If /etc/noautoreboot doesn't exist, run shutdown -r +5.

    This answer explains how short-circuit and and or operators can perform if-then logic. For a brief, intuitive and highly informal explanation, you can read the command this way:

    /etc/noautoreboot exists! Or, run shutdown -r +5.

    See man [ to see how the test itself is performed.

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I love doing this by telling the Session Manager we want to reboot. This can be done without root permissions, and we get a nice window that warns us that the system is going to be rebooted -even we can cancel the reboot if we like to.

The Graphical Way - Preferred Method

Install gnome-schedule from the Ubuntu Software Center. If you don't want to install anything additional, do it the Terminal Way.

Open gnome-schedule from the dash, create a new repeated task, and set these options:

  • Description: Whatever you want
  • Command: dbus-send --print-reply --dest="org.gnome.SessionManager" /org/gnome/SessionManager org.gnome.SessionManager.Reboot
  • Choose X Application just below the command.
  • Time and Date, Advanced:
    • Minute: 0,30

Leave the other options at their default values. Click on Add.


The Terminal Way - No Need for Additional Software

Run from the terminal:

crontab -e

Add this line:

0,30 * * * * DISPLAY=:0 dbus-send --print-reply --dest="org.gnome.SessionManager" /org/gnome/SessionManager org.gnome.SessionManager.Reboot

Save & exit. Assuming you are using nano (the default one), press Ctrl+o and Ctrl+x.

Please notice this won't work if your DISPLAY is actually different from :0, and that's the reason this method is not preferred. But, honestly, if you are rebooting your computer every 30 minutes, your DISPLAY will most probably always be :0.

Not using Gnome or Unity?

Both methods explained above depends on some gnome components, found both on Gnome sessions and on Unity. If you want to do this on another environments (such as Kubuntu's KDE, Kubuntu's LXDE...) you better replace the command with this one instead:

dbus-send --system --print-reply --dest="org.freedesktop.ConsoleKit" /org/freedesktop/ConsoleKit/Manager org.freedesktop.ConsoleKit.Manager.Restart

This won't ask for confirmation, and will restart inmediatly, but will work on all environments, assuming you have not manually uninstalled ConsoleKit, of course.

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Run sudo crontab -e from the command line and add this line to the file:

0,30 * * * * reboot

This tells the system to run the command reboot every 30 minutes as root. For an overview of the time syntax, see here: http://linuxmoz.com/crontab-syntax-tutorial/

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This will not work, as reboot must be run as root, and this adds it to the user's personal crontab, so it runs as that non-root user. (The same thing with sudo reboot will also not work because sudo will try to prompt for a password and fail.) /etc/crontab should be used for this instead (please note its syntax is slightly different). –  Eliah Kagan Jan 15 '13 at 19:35
    
You could issue sudo crontab -e and then create a cron entry. –  Tass Dec 16 '13 at 18:39
    
Thanks, I updated my answer. –  Kevin Chen Dec 24 '13 at 1:47
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Use cron to schedule a job every 30 minutes. Point that job at a shell script that simply has

reboot

in it.

Since cron runs as root, you shouldn't need to do anything special in terms of permissions.

Update

Yes I do, in fact I never on any of my systems allow user based crontabs (There are better ways of allowing users to do user level scheduled tasks) cron was designed from the very beginning purely for system automation and not for users to schedule ordinary tasks. Things such as log rotations (which still happens today)

Reboot MUST be run as root to work correctly, the alternative is to set it's sticky bit, so that when run as a regular user it actually executes as root and works as expected, but in doing that your then opening your server up to allowing regular users to reboot it at will.

You could even possibly automate a call to SUDO, but I need to dig into that one, not sure if you can automate the need for a password with SUDO (I don't use it often, i prefer to just drop straight to a root shell using SU)

If you set it up in system wide crontab then everything is run as root, so my statement is accurate (I just neglected to mention that the system wide one should be used)

As for your question "Why Wrap it in a script?" well, why not? If the OP puts it in a shell script, then at some point in the future needs to add to it, he simply adds to the script, instead of having to open crontab locate the job, remove it, replace it with a shell script, then write a script with the old + new in.

Over 20 years as a Sys Admin / Developer working with systems as far back as Ultrix / Solaris and even VAX has taught me one major point.

If you can make it easier at the beginning, then it remains easy for it's life time.

I really don't get this "Minimalistic" attitude that a lot of modern day sys admins have, where doing as little as possible is the key to success. Most servers these days are easily 20 times+ more powerful than anything I ever started out on, and this kind of scenario (Wrapping in shell scripts) was recommended practice then, so there's really no argument for not doing it now.

Unless you really want to go hardcore Unix/Linux, in which case tag it all onto the cron entry, and pipe everything together the way it ought to be done :-)

However, I do digress, and also understand that many guys these days a thrown in at the deep end and told to make things work, as such they lack the time (and usually the inclination) to sit down and learn about new techniques (or old in this case) or even want to play with this stuff outside of work.

I personally, have a single server among the ones I run that's dedicated purely for me to play around on, so I can test things like this... which is better A or B, so it's not without reason that I advise on any of this.

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See my update.. you can give me my 1 point back now if you wish ;-) –  shawty Jan 16 '13 at 13:10
    
Try again... be patient... –  shawty Jan 16 '13 at 13:24
2  
This is now no longer an answer at all! (Also, you're confusing the sticky bit and the setuid bit.) –  Eliah Kagan Jan 16 '13 at 13:52
    
Yes it is an answer, I typed it, added it as an answer therefore it's an answer!!! –  shawty Jan 16 '13 at 14:26
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