{dev_notes}

Docker Crons

Published 4 months ago.
Last updated

Crontab

Use crontab -l to verify the cron settings:

# crontab -l
# do daily/weekly/monthly maintenance
# min   hour    day     month   weekday command
*/15    *       *       *       *       run-parts /etc/periodic/15min
0       *       *       *       *       run-parts /etc/periodic/hourly
0       2       *       *       *       run-parts /etc/periodic/daily
0       3       *       *       6       run-parts /etc/periodic/weekly
0       5       1       *       *       run-parts /etc/periodic/monthly

* * * * * cd /var/www/scripts && /usr/bin/php /var/www/scripts/cronjobphp.php | tee -a /var/log/cron.log >/proc/1/fd/1 2>/proc/1/fd/2

php script via cron root

  • Add a PHP script to root crontab.
  • Log the output to /var/log/cron.log.
  • NOTE: For PHP (and maybe everything) You must first cd to the directory before running the file to keep relative paths working as expected with cron. You must also envolk PHP from its path /usr/bin/php, and not via just using php.

dockerfile

RUN echo "* * * * * cd /var/www/scripts && /usr/bin/php /var/www/crons/cronjobphp.php >> /var/log/cron.log" >> /etc/crontabs/root

/var/www/crons/cronjobphp.php

<?php
$myDate = date("Y-m-d h:i:s");
echo "cronjobphp - current date and time: " . $myDate . "\n";

Running cat /var/log/cron.log shows the results:

cronjobphp - current date and time: 2025-01-09 12:05:00
cronjobphp - current date and time: 2025-01-09 12:06:00
cronjobphp - current date and time: 2025-01-09 12:07:00
cronjobphp - current date and time: 2025-01-09 12:08:00

If cron is running as a secondary (background) process in the docker container, to get the log to output to the dockerlog you need to specifically send it there.

dockerfile

RUN echo "* * * * * cd /var/www/scripts && /usr/bin/php /var/www/crons/cronjobphp.php >/proc/1/fd/1 2>/proc/1/fd/2" >> /etc/crontabs/root

Also, you can log to a file and dockerlog at the same time.

dockerfile

RUN echo "* * * * * cd /var/www/scripts && /usr/bin/php /var/www/crons/cronjobphp.php | tee -a /var/log/cron.log >/proc/1/fd/1 2>/proc/1/fd/2" >> /etc/crontabs/root

sh script via cron root

  • Add an SH script to root crontab.
  • Log the output to /var/log/cron.log.

dockerfile

RUN echo "* * * * * sh /var/www/crons/cronjob1.sh >> /var/log/cron.log" >> /etc/crontabs/root

var/www/crons/cronjob1.sh

#!/bin/sh
echo "cronjob1 - current date and time: $(date)"

Running cat /var/log/cron.log shows the results:

Current date and time: Wed Jan  8 16:16:31 MST 2025
Current date and time: Wed Jan  8 16:17:00 MST 2025
Current date and time: Wed Jan  8 16:18:00 MST 2025
Current date and time: Wed Jan  8 16:19:00 MST 2025
Current date and time: Wed Jan  8 16:20:00 MST 2025
Current date and time: Wed Jan  8 16:21:00 MST 2025

sh script cron via periodic dir

  • Add an SH script to the /etc/periodic/1min directory.
  • Log the output to /var/log/cron.log.
  • NOTE: sh files in a periodic directory must NOT have the .sh extension.

dockerfile

RUN mkdir /etc/periodic/1min
COPY crons/cronjob1.sh /etc/periodic/1min/cronjob1
RUN chmod +x /etc/periodic/1min/cronjob1
RUN echo "* * * * * run-parts /etc/periodic/1min >> /var/log/cron.log" >> /etc/crontabs/root

var/www/crons/cronjob1.sh

#!/bin/sh
echo "cronjob1 - current date and time: $(date)"

Running cat /var/log/cron.log shows the results:

Current date and time: Wed Jan  8 16:16:31 MST 2025
Current date and time: Wed Jan  8 16:17:00 MST 2025
Current date and time: Wed Jan  8 16:18:00 MST 2025
Current date and time: Wed Jan  8 16:19:00 MST 2025
Current date and time: Wed Jan  8 16:20:00 MST 2025
Current date and time: Wed Jan  8 16:21:00 MST 2025