Crontab size limit

cron

Is there a limit to the number of entries in a user's crontab? I have a personal crontab with ~100 entries, and I just added a job to it that does not appear to be running. I can see in syslog when cron launches all the other jobs, but not this last one.

This is ubuntu's default vixie cron.

Best Answer

There doesn't appear to be a documented limit to the number of crontab entries allowed. So, short of checking the source code to the specific version you're using, perhaps the BUG entry in the crontab manpage could be helpful:

Although cron requires that each entry in a crontab end in a newline character, neither the crontab command nor the cron daemon will detect this error. Instead, the crontab will appear to load normally. However, the command will never run. The best choice is to ensure that your crontab has a blank line at the end.

Related Solutions

Ubuntu – crontab not running on VirtualBox unless I’m logged in

It would appear that you are trying to run a cron job as your user, and that you have some form of encrypted home directory set up.

Your home directory (or some subset thereof) is unlocked and mounted when you log in, but when you are logged out, your home directory is unavailable, thus the error in your logs.

You should remove the encryption, run the cron job as another user, or you could try to run the job as your user but specifying a different environment (HOME, most notably).

Cron Job – How to Run a Cron Job Manually and Immediately

Here's what I did, and it seems to work in this situation. At least, it shows me an error, whereas running from the command line as the user doesn't show the error.

Step 1: I put this line temporarily in the user's crontab:

* * * * *   /usr/bin/env > /home/username/tmp/cron-env

then took it out once the file was written.

Step 2: Made myself a little run-as-cron bash script containing:

#!/bin/bash
/usr/bin/env -i $(cat /home/username/tmp/cron-env) "$@"

So then, as the user in question, I was able to

run-as-cron /the/problematic/script --with arguments --and parameters

This solution could obviously be expanded to make use of sudo or such for more flexibility.

Hope this helps others.

Best Answer

Related Solutions

Ubuntu – crontab not running on VirtualBox unless I’m logged in

Cron Job – How to Run a Cron Job Manually and Immediately

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