cron

cron : 

Daemon to execute scheduled commands. Cron enables users to schedule jobs (commands or shell scripts) to run periodically at certain times or dates.

1 * * * * echo “hi” >/dev/tty1 displays the text “hi” after every 1 minute in tty1

.—————- minute (0 – 59)

| .————- hour (0 – 23)

| | .———- day of month (1 – 31)

| | | .——- month (1 – 12) OR jan,feb,mar,apr …

| | | | .—– day of week (0 – 7) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat

* * * * * command to be executed

Source of example: Wikipedia