Dockerfile example for run cron job on ubuntu

Dockerfile

FROM ubuntu:16.04
MAINTAINER natataworld@love.com

ARG USER=docker_user
 
RUN apt-get update && apt-get -y install cron sudo

# create a normal user
RUN adduser --disabled-password --gecos '' $USER
RUN adduser $USER sudo
RUN echo '%sudo ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers
USER $USER

# Add crontab file in the cron directory
ADD crontab /home/$USER/hello-cron

RUN sudo chown $USER:$USER /home/$USER/hello-cron
 
# Give execution rights on the cron job
RUN chmod 0644 /home/$USER/hello-cron
 
# Create the log file to be able to run tail
RUN touch /home/$USER/cron.log
 
# Run the command on container startup
RUN crontab /home/$USER/hello-cron

CMD sudo service cron start && /bin/bash

# How to use:
# # docker build --rm -t natata/cron-example .
# # docker run -it natata/cron-example:latest
# in the container:
# # tail -f /home/docker_user/cron.log