crontab not working on Centos Docker container

After a day wasted in suboptimal Googling and experimentation, the answer to this conundrum was commenting out the following line in the file /etc/pam.d/crond (and then running service crond restart):

session required pam_loginuid.so

This is because of some Docker-Centos security issue. I don't have further details on why this works. (Check this for details.)

Also, troubleshooting this made me realize a few gotchas which might be useful:

• Check that you have crond running as a service (if not, use/etc/init.d/crond start)

• Each line in your crontab should be followed be a newline character

• Your scripts and log file should have suitable write/executepermissions

• crontab file shouldn't have weird Windows environment characters(like ^M)

• In some rare cases, crond might have different time zone than yoursystem

• Also check /etc/cron.allow and /etc/cron.deny files to verify whocan add/edit cron jobs

May your day be invested in more fruitful pursuits, stranger.

I recommend run cron under host and run command inside the container

example:

0 17 1 * * /usr/bin/docker exec container_name /root/proj/env/bin/python /root/proj/files/frontend/file1.py > /var/log/cron.log