I have a LAMP container with supervisor.
I add a simple cron
* * * * * root /bin/date >> /var/log/cron.log
from my Dockerfile
ADD ./crons/test /etc/cron.d/test
RUN chmod 0777 /etc/cron.d/test
I start cron via supervisor with a supervisor-cron.conf like this:
[program:cron]
command=/bin/bash -c "cron -f"
numprocs=1
autostart=true
autorestart=true
startretries=2
Cron starts fine and stays up and running. The strange thing is that no cronjob is running automatically [as it should] but when I execute docker exec lamp crontab /etc/cron.d/test the cron job starts and works as expected.
Am I missing something? Everywhere I have read that cron jobs are executed automatically by cron.
I solved it.
I tried both setting them up in /etc/crontab and /etc/cron.d/ .
Cron didn’t auto-start the cron jobs .
However, when I run docker exec lamp crontab /etc/cron.d/my_cronjob_file all played nice. This made me suspicious , and then I read this . So, after adding my_cronjob_file in the container [in the dockerfile] I added RUN crontab /etc/cron.d/my_cronjob_file . This essentially ‘installs’ the cronjob to the crontab table. [I don’t know the internals of cron/tab but that’s the gist I understood.] .
After that , the cron service comes up by supervisor and the cronjob runs like a charm.
This can be solved with the bash file, due to the layered architecture of the Docker, cron service doesn't get initiated with RUN/CMD/ENTRYPOINT commands.
Simply add a bash file which will initiate the cron and other services (if required)
DockerFile
FROM gradle:6.5.1-jdk11 AS build
# apt
RUN apt-get update
RUN apt-get -y install cron
# Setup cron to run every minute to print (you can add/update your cron here)
RUN touch /var/log/cron-1.log
RUN (crontab -l ; echo "* * * * * echo testing cron.... >> /var/log/cron-1.log 2>&1") | crontab
# entrypoint.sh
RUN chmod +x entrypoint.sh
CMD ["bash","entrypoint.sh"]
entrypoint.sh
#!/bin/sh
service cron start & tail -f /var/log/cron-2.log
If any other service is also required to run along with cron then add that service with & in the same command, for example: /opt/wildfly/bin/standalone.sh & service cron start & tail -f /var/log/cron-2.log
Once you will get into the docker container there you can see that testing cron.... will be getting printed every minute in file: /var/log/cron-1.log