Cron: running scripts on a schedule

Cron runs commands and scripts on a schedule: every ten minutes, every night, every Monday. On web hosting you add jobs in cPanel; on your own server you use the crontab command.

In cPanel

Go to Advanced → Cron Jobs. Pick a schedule from the ready-made options or fill in the fields by hand, then enter what to run in the Command field:

/usr/local/bin/php /home/username/public_html/cron.php

/usr/local/bin/php is the default PHP version. If your script needs a particular version, give its path instead — for PHP 8.3, for example: /opt/cpanel/ea-php83/root/usr/bin/php. cPanel emails the output of each job to the address set in the same section; to stop the emails, add >/dev/null 2>&1 to the end of the command.

Line format

minute  hour  day_of_month  month  day_of_week  command

An asterisk means “any value”, */10 means “every 10”, and days of the week run from 0 (Sunday) to 6. Times follow the server’s clock.

# every 10 minutes
*/10 * * * * /usr/local/bin/php /home/username/public_html/cron.php
# every day at 03:30
30 3 * * * /usr/local/bin/php /home/username/public_html/cron.php
# every Friday at midnight
0 0 * * 5 /usr/local/bin/php /home/username/public_html/cron.php
# on the first day of every month at 00:00
0 0 1 * * /usr/local/bin/php /home/username/public_html/cron.php

Why a job doesn’t run

• Relative paths. Cron doesn’t run commands from your website’s folder, and its PATH holds only a short list of directories. Use full paths to the program (/usr/local/bin/php, not php), to the script, and to any files the script opens. In PHP it’s handy to build paths from __DIR__.
• An asterisk in the minutes field. * 3 * * * means every minute from 03:00 to 03:59, not once during the night. You need 0 3 * * *.
• You can’t see any errors. Save the output to a file: … >> /home/username/cron.log 2>&1 — and look at what the script writes.
• No permission to run. A script that runs directly, rather than through php, must be executable (chmod 755 script.sh) and start with a line such as #!/bin/bash.
• A file from Windows. If you edited the script in Windows, it may fail because of the line endings — see Files from Windows: line endings for the fix.

On your own server

crontab -e   # open your jobs in an editor
crontab -l   # list your jobs

To run jobs as root, use sudo crontab -e. If the crontab command is missing, install cron: sudo apt install cron on Debian and Ubuntu, or sudo dnf install cronie on AlmaLinux. To see the log of runs, use journalctl -u cron (Debian, Ubuntu) or journalctl -u crond (AlmaLinux); on FreeBSD the log is the file /var/log/cron.