Cfrtjryk

man 5 crontab is pretty clear on how to use crontab to run a script on boot:

   These special time specification "nicknames" are supported, which replace the 5 initial time and date

   fields, and are prefixed by the `@` character:

   @reboot    :    Run once after reboot.

So I happily added a single line to my crontab (under my user account, not root):

@reboot     /home/me/myscript.sh

But for some reason, myscript.sh wouldn't run on machine reboot.
(it runs fine if I invoke it from the command line, so it's not a permissions problem)

What am I missing?

Update to answer @Anthon's questions:

1. Oracle-linux version: 5.8 (uname: 2.6.32-300.39.2.el5uek #1 SMP)


2. Cron version: vixie-cron-4.1-81.el5.x86_64


3. Yes, /home is a mounted partition. Looks like this is the problem. How do I workaround this?


4. Currently, myscript.sh only echos a text message to a file in /home/me.

This can be a bit of a confusing topic because there are different implementations of cron. Also there were several bugs that broke this feature, and there are also some use cases where it simply won't work, specifically if you do a shutdown/boot vs. a reboot.

Bugs

datapoint #1

One such bug in Debian is covered here, titled: cron: @reboot jobs are not run. This seems to have made it's way into Ubuntu as well, which I can't confirm directly.

datapoint #2

Evidence of the bug in Ubuntu would seem to be confirmed here in this SO Q&A titled: @reboot cronjob not executing.

excerpt

comment #1: .... 3) your version of crond may not support @reboot are you using vix's crond? ... show results of crontab -l -u user

comment #2: ... It might be a good idea to set it up as an init script instead of relying on a specific version of cron's @reboot.

comment #3: ... @MarkRoberts removed the reboot and modified the 1 * * * * , to */1 * * * * , problem is solved! Where do I send the rep pts Mark? Thank you!

The accepted answer in that Q&A also had this comment:

Seems to me Lubuntu doesn't support the @Reboot Cron syntax.

Additional evidence

datapoint #3

As additional evidence there was this thread that someone was attempting the very same thing and getting frustrated that it didn't work. It's titled: Thread: Cron - @reboot jobs not working.

excerpt

Re: Cron - @reboot jobs not working

Quote Originally Posted by ceallred View Post
This is killing me... Tried the wrapper script. Running manually generates the log file... rebooting and the job doesn't run or create log file.

Syslog shows that CRON ran the job... but again, no output and the process isn't running.
Jul 15 20:07:45 RavenWing cron[1026]: (CRON) INFO (Running @reboot jobs)
Jul 15 20:07:45 RavenWing CRON[1053]: (ceallred) CMD (/home/ceallred/Scripts/run_spideroak.sh > /home/ceallred/Scripts/SpiderOak.log 2>&1 &)

It's seems like cron doesn't like the @reboot command.... Any other ideas?

Okay... Partially solved. I'll mark this one as solved and start a new thread with the new issue.....

I think the answer was my encrypted home directory wasn't mounted when CRON was trying to run the script (stored in /home/username/scripts). Moved to /usr/scripts and the job runs as expected.

So now it appears to be a spideroak issue. Process starts, but by the time the boot process is finished, it's gone. I'm guessing a crash for some reason.... New thread to ask about that.

Thanks for all the help!

Once this above user figured out his issue he was able to get @reboot working out of the crontab entry of a user.

I'm not entirely sure what version of cron is used on Ubuntu, but this would seem to indicate that user's can use @reboot too, or that the bug was fixed at some point in subsequent versions of cron.

datapoint #4

I tested on CentOS 6 the following and it worked.

Example

$ crontab -l

@reboot echo "hi" > /home/sam/reboot.txt 2>&1

I then rebooted the system.

$ sudo reboot

After the reboot.

$ cat reboot.txt 

hi

Take aways

1. This feature does seem to be supported for both system and user crontab entries.


2. You have to make sure that it's supported/working in your particular distro and/or version of the cron package.

For more on how the actual mechanism works for @reboot I did come across this blog post which discusses the innards. It's titled: @reboot - explaining simple cron magic.

Debugging crond

You can turn up the verbosity of crond by adding the following to this configuration file on RHEL/CentOS/Fedora based distros.

$ more crond 

# Settings for the CRON daemon.

# CRONDARGS= :  any extra command-line startup arguments for crond

CRONDARGS="-L 2"

The valid levels are 0, 1, or 2. To revert this file back to it's default logging level simply remove the "-L 2" when you're done debugging the situation.

I found out that on my Ubuntu machine, I do not have access to dns services, yet, at @reboot time. This prevented me from mounting remote volumes. This corny, yet simple, solution worked:

@reboot sleep 60 && /home/me/bin/mount.sh 2>&1 >> /home/me/reboot.log

(in root cron; last parts only for debugging)

I have mac osx as well and I had same issue where my script were not running. but When i fixed my script to like

@reboot   cd /home/me/  && sh myscript.sh

it worked fine for me. make sure to make your shell file to be executable by running the command

chmod +x myscript.sh

hope these helps.

Take a fresh install of Ubuntu Gnome 13.10 (default user in my case: avanderneut).

avanderneut@uggo:~$ crontab -l

no crontab for avanderneut

avanderneut@uggo:~$ crontab -e

no crontab for avanderneut - using an empty one



Select an editor.  To change later, run 'select-editor'.

  1. /bin/ed

  2. /bin/nano        <---- easiest

  3. /usr/bin/vim.tiny



Choose 1-3 [2]: 3

crontab: installing new crontab

avanderneut@uggo:~$ crontab -l | tail -2

# m h  dom mon dow   command

@reboot /home/avanderneut/bin/on_reboot

avanderneut@uggo:~$ vi /home/avanderneut/bin/on_reboot

avanderneut@uggo:~$ more !$

more /home/avanderneut/bin/on_reboot

#! /bin/bash

echo "Reboot script" > /var/tmp/xxx

avanderneut@uggo:~$ chmod 755 /home/avanderneut/bin/on_reboot

avanderneut@uggo:~$ ls /var/tmp

avanderneut@uggo:~$ /home/avanderneut/bin/on_reboot

avanderneut@uggo:~$ ls /var/tmp

xxx

avanderneut@uggo:~$ rm /var/tmp/xxx

avanderneut@uggo:~$ sudo reboot

[sudo] password for avanderneut: 

And see that after reboot the file /var/tmp/xxx is there although it was not there before rebooting.

This was done with cron version 3.0.

You have to make sure that no services discs etc are used that might not be available at the time the script runs. Start with something simple like the above and make sure it has no terminal output as email is probably not up and running.

You might aslo need a more up-to-date cron (or an upgrade from oracle-linux) if this did not work for you and you need this feature.