Php – Cron job keeps running!

The usual problem with 'cron' jobs is that they have zero environment - unlike 'at' jobs which do copy your environment. When something works from the command line and not from 'cron', my experience is that 'environment' is one of the most common problems. Occasionally you run into another problem - 'cron' jobs are not run with a terminal, and occasionally programs get stroppy about this. However, this is in the 1% range compared with 99% for environment issues.

The other key technique I use is to always run a shell script from 'cron'; the shell script ensures that the environment is set correctly and then runs the real program. If a 'cron' job is giving me problems, I can then tweak the script to do useful things like this:

{
    date
    env | sort
    set -x
    ...what was there before adding the debug...
} >/tmp/cron.jobname.$$ 2>&1

This redirects all the output - standard output and standard error - to a file name. You can build timestamps into the filename if you prefer that to the process ID. Analyzing the log files often reveals the problems swiftly.

The command wget is a good solution for this problem if you are accessing a script on a remote server. However, if you are running the cronjob on the actual host that is "mydomain.com" you may just want to schedule crobjob to execute the code sitting at /process/2909.

For example, we have some PHP jobs that we execute with cron. Rather than using an HTTP request that could take minutes (and potentially cause timeout issues) we setup a cronjob that calls "php5 /srv/cronJobs/2909.php" - This invokes the PHP interpreter and is not subject to HTTP timeouts. Additionally, this PHP process is separate from Apache so the scheduled job will not die in case a sysadmin restarts httpd.