Running a command in regular intervals.

Connect to your server through ssh and enter

 crontab -e

Now you can enter a command to run in the following format:

minute hour day month weekday command

For example:

0 2,18   * /usr/bin/lua /path/script.lua >> /path/script.log 2>&1

Will run the lua script script.lua every day at 2am and 6pm and log it's output to script.log.