Does a cron job kill last cron execution?

Question

I have a cron job the executes a PHP script. The cron is setup to run every minute, this is done only for testing purposes. The PHP script it is executing is designed to convert videos uploaded to the server by users to a flash format (eg... .flv). The script executes fine when manually doing it via command line, however when executing via cron it starts fine but after one minute it just stops.

It seems that when the next cron is executed it "kills" the last cron execution. I added the following PHP function:

ignore_user_abort(true);

In hopes that it would not abort the last execution, I tested setting the cron to run every 5 minutes, which works fine, however a conversion of a video may take over 5 minutes so I need to figure out why its stoping when another cron is executed.

Any help would be appreciated.

Thank you!

EDIT: My cron looks like:

*/1 * * * * php /path_to_file/convert.php

Answer 1

I don't think cron kills any processes. However, cron isn't really suitable for long running processes. What may be happening here is that your script tramples all over itself when it is executed multiple times. For example, both PHP processes may be trying to write to the same file at the same time.

First, make sure you not only look in the php error log but also try to capture output from the PHP file itself. E.g:

*/1 * * * * * php /path/to/convert.php & >> /var/log/convert.log

You could also use a simplistic lockfile to ensure that convert.php isn't executed multiple times. Something like:

if (file_exists('/tmp/convert.lock')) {
    exit();
}

touch('/tmp/convert.lock');
// convert here
unlink('/tmp/convert.lock');