jojje/gmail-cron repository overview

⁠Cron Gmailing container

E-mail enabled alpine based container for running Cron jobs.

⁠Usage

docker run -d \
-e "[email protected]" \
-e "SMTP_PASSWORD=secret" \
-e "[email protected]" \
jojje/gmail-cron

⁠Compose example

cron:
  image: jojje/gmail-cron
  environment:
    SMTP_LOGIN: [email protected]
    SMTP_PASSWORD: secret
    CRON_MAILTO: [email protected]
    CRON_SENDER: Cron user

⁠Configuration

The following environment variables control the cron behavior:

• SMTP_LOGIN: The login address for a valid gmail account used to send cron mail via gmail.
• SMTP_PASSWORD: The corresponding password for the gmail account.
• CRON_MAILTO: Email address to send cron mail to.
• CRON_SENDER: When provided changes the display name for the sender account.

If CRON_SENDER is not specified, the sender will be "Linux User <$SMTP_LOGIN>"

⁠Adding cron jobs

The container is prepared to run run cron-jobs both as root and as a non-root user. Root's jobs are governed by /etc/crontabs/root and the non-root account, named 'user' with uid and gid 1000, by the file /etc/crontabs/user.

The options for adding jobs are listed below.

⁠Add a periodic job

Place an executable file (script typically) in one of the directories under /etc/periodic/ for root, or ~/periodic/ for the non-root account.

For example, to run the script hello-world every 15 minutes as root, place it in /etc/periodic/15min/

⁠Add custom job schedule

If the periodic intervals are not sufficient, you can modify the crontab file itself for the user that is to run the job(s).

E.g. adding a new job to be run every 5 minutes:

# echo '5 * * * *  /some-dir/my-script' >> /etc/crontabs/user

Or using the normal edit commands for crontab

$ crontab -e or crontab -l | <edit command> | crontab -

Or simply replace the default crontab file(s) with your own.

These actions would normally be done as part of your own Dockerfile, where you create override layers from this image as a base.

E.g.

FROM jojje/gmail-cron
COPY my-job /usr/local/bin/
COPY crontab /etc/crontabs/user

⁠Trouble shooting

⁠Get more runtime info

Starting of crond is just the default argument to the container, so you can replace that with a custom command. E.g. sh to dig into how the container looks after initialization, or increasing the crond logging.

Example of the latter

docker-compose run --rm cron crond -f -L /dev/stdout -l 0

Note: assumes a compose file like in the example is used, to reduce typing.

⁠Ensure mail delivery

To make sure that you've white-listed the cron emails, so they don't end up in a spam folder, or are prevented from delivery for some reason or another, it's good to at least fire off a test email before deploying the container to production.

echo -e "Subject:Test\n\nbody\n" | \
  docker-compose run --rm cron sendmail [email protected]