How do I add a task to Crontab

Question

I am making a program for the Raspberry Pi to use, as part of its installation, it need to add a task to crontab so that it will run on bootup.

I know if I type in crontab -e then add the line "@reboot file/to/program" to the bottom it will do it.

But how do I do it with just a command in the terminal for my installation script to use?

Answer 1

This isn't particularly specific to the Raspberry Pi, and a bit of googling reveals some very complete cron overviews. From your description, it sounds like you want to edit the system-wide crontab (e.g.sudo nano /etc/crontab) to add the @reboot clause.

Answer 2

I have a number of crons that I add via my install script. Works perfect.

sudo sh -c 'cat <<EOF > /var/spool/cron/crontabs/root
00 * * * * curl http://example.org/ping/`hostname`
* * * * * /usr/bin/php /var/www/crontab.php
EOF'
sudo /etc/init.d/cron restart

If you want to do a manual check whether those crons have been added correctly:

sudo crontab -e

shows that everything is added as it should be.

Answer 3

Yet another option- you can place a file in /etc/cron.d/. The advantage of this is you own the whole file, so it's easier to install it and not worry about breaking other entries.

Example:

cat /etc/cron.d/hello
*/5 * * * * pi /home/pi/hello.sh

Note entries in system-level places like this also specify the username.