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Troubleshooting custom cron scripts

Posted by Jack on 04/14/2008
in

I often have trouble when creating my own scripts to be run by cron on Linux servers. On most of the servers that I administer, I use a homegrown backup script (based on these excellent instructions) that I place in /etc/cron.daily. After upgrading a server to Debian Etch recently I found that my backup script, named backup-script.sh, was no longer working.

After stumbling around in the dark for a while, I found a useful tool to use when trying to troubleshoot cron jobs:

run-parts --list /etc/cron.daily

This command lists the valid scripts in a directory. I noticed that backup-script.sh was the only script in the directory that was missing from the list. After checking that ownership and permissions on all of the scripts were the same (using ls -l), it clicked that the only difference between my backup script and the other valid scripts was that the backup script's name ended with the extension .sh. After removing that, I used run-parts --list again and my backup script was now included in the list of valid files. Sweet! And a definite relief given how important reliable backups are!

Comments

Submitted by Daniel Kahn Gillmor on Mon, 04/14/2008 - 1:28pm

The run-parts rules for what script names have to be used are pretty strict.

From run-parts(8):

If neither the --lsbsysinit option nor the --regex option is given then the names must consist entirely of upper and lower case letters, digits, underscores, and hyphens.

These strict limitations actually come in handy when you might use a text editor which drops backup files with arbitrarily-named suffixes into the directory (e.g. if you edit the file foo with emacs, it will leave foo~ lying around). you don't want those files being run automatically!

Submitted by admin on Tue, 04/15/2008 - 8:42am

Hey, good to know the details behind the functionality, Daniel! Especially given that text editor goofiness. Though wouldn't foo~ not be run because it includes a tilde, which isn't an allowed character?

Submitted by nate beaty on Sat, 11/15/2008 - 4:26pm

ahhhh... thank you! i recently had a hard drive crash only to find out my daily script wasn't running. guess what? it ends in ".sh" -- argh! thanks much for this, been beating my head against the screen for days.

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