Why doesn't the cron service in Dockerfile run?

Question

While searching for this issue I found that: cron -f should start the service.

So I have:
RUN apt-get install -qq -y git cron

Next I have:
CMD cron -f && crontab -l > pullCron && echo "* * * * * git -C ${HOMEDIR} pull" >> pullCron && crontab pullCron && rm pullCron

My dockerfile deploys without errors but the cron doesn't run. What can I do to start the cron service with an added line?

PS:
I know that the git function in my cron should actually be a hook, but for me (and probably for others) this is about learning how to set crons with Docker :-)

PPS:
Complete Dockerfile (UPDATED):

RUN apt-get update && apt-get upgrade -y
RUN mkdir -p /var/log/supervisor
RUN apt-get install -qq -y nginx git supervisor cron wget
RUN echo "daemon off;" >> /etc/nginx/nginx.conf
RUN wget -O ./supervisord.conf https://raw.githubusercontent.com/..../supervisord.conf
RUN mv ./supervisord.conf /etc/supervisor/conf.d/supervisord.conf
RUN apt-get install software-properties-common -y && apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com:80 0x5a16e7281be7a449 && add-apt-repository 'deb http://dl.hhvm.com/ubuntu utopic main' && apt-get update && apt-get install hhvm -y
RUN cd ${HOMEDIR} && git clone ${GITDIR} && mv ./tybalt/* ./ && rm -r ./tybalt && git init
RUN echo "* * * * * 'cd ${HOMEDIR} && /usr/bin/git pull origin master'" >> pullCron && crontab pullCron && rm pullCron
EXPOSE 80
CMD ["/usr/bin/supervisord"]

PPPS:
Supervisord.conf:

[supervisord]
autostart=true
autorestart=true
nodaemon=true

[program:nginx]
command=/usr/sbin/nginx -c /etc/nginx/nginx.conf

[program:cron]
command = cron -f -L 15
autostart=true
autorestart=true

Answer 1

Cron is not running because only the last CMD overrides the first one (as @xuhdev said). It's documented here : https://docs.docker.com/reference/builder/#cmd.

There can only be one CMD instruction in a Dockerfile. If you list more than one CMD then only the last CMD will take effect.

If you want to have nginx and cron running in the same container, you will need to use some kind of supervisor (like supervisord or others) that will be the pid 1 process of your container and manage the chield processes. I think this project should help : https://github.com/nbraquart/docker-nginx-php5-cron (it seems to do what you're trying to achieve).

Depending on what you're cron is here for, there would be other solution to that — like building a new image for each commit or each tags, etc...