Set up the Script to Run Periodically

About

The goal of the page is to outline some basic steps and provide recommendations in order to configure your system to run the script based on time.

Set up a Cron-Job

You have to be familiar with cron daemons configuration. I'll remind some steps here, assuming Vixie Cron or its fork is installed.

To run the script once every two days, edit crontab for your user with a command like crontab -e. You may want to define SHELL and PATH variables there. If you want color output, define TERM variable. Consider the following example:

SHELL=/bin/bash
TERM=xterm-256color
CHECK_SITE=/tmp/simon/simon.sh -avd -i /tmp -s /tmp/simon.old

* * */2 * * $CHECK_SITE >>/tmp/simon.log 2>&1

Output redirection is used to send all output to a log file.

To disable the cron-job, comment it out in the crontab:

#* * */2 * * $CHECK_SITE >>/tmp/simon.log 2>&1

Note: the instruction above implies that your system is running continuously. Don't forget to test the cron-job by making it fire 1-2 minutes into the future.

Set up a Systemd Timer

If your distributive uses systemd, you may decide to set up a timer. Examples of unit files shown below have a benefit of being able to catch up on the missed run of a task. That means if the task was scheduled at a period of time when your system was not running, the task will be executed on a system's startup.

There are two files: simon.timer and simon.service. You need to place them under one of the valid user unit search paths (see systemd.unit(5)). E.g., let's place these files in ~/.config/systemd/user/ directory.

The unit file for the timer is self-explanatory:

# simon.timer
[Unit]
Description=Run simon once every two days

[Timer]
Persistent=true
RandomizedDelaySec=90
OnCalendar=*-*-01/2 16:00:01

[Install]
WantedBy=default.target

The service unit file clears TERM variable because the color output seems to be unsupported by systemd-journlad. Note: %h is a variable that points to your home path (just like echo $HOME). Also, it's not a good idea to use -v: error messages in the system logs should be enough to get a picture of what's happening.

# simon.service
[Unit]
Description=Check simonstalenhag.se and download new artworks

[Service]
Type=simple
# TERM=dumb by default
Environment=TERM=''
# Disable color output, log only errors to systemd journal
ExecStart=%h/Downloads/simon-master/simon.sh -ac \
    -i %h/Downloads/simon-master/ -s %h/Downloads/simon-master/simon.old
# e.g, if there's no internet access, restart the service after 25m
Restart=on-failure
RestartSec=25m

Systemd doesn't track these files and you have to reload the daemon in order to apply your new units: systemctl --user daemon-reload. Reloading is also required if you changed anything in the files and want to use updated units.

Enable the timer and activate it systemctl --user enable --now simon.timer.

To see logs, use journalctl --user -u simon.service.

Disable the timer, run systemctl --user disable --now simon.timer.