Guide to using Crontab

crontab is a tool for scheduling tasks in Unix and Unix-like systems. By writing cron expressions, you can perform tasks on a regular basis.

basic syntax

* * * * * command_to_execute
- - - - -
| | | | |
| | | | └ -- What day of the week (0-7) (Sunday = 0 or 7)
| | | └ -- Month (1-12)
| | └ -- -- Date (1-31)
| └ -- -- hour (0-23)
└ -- -- Minutes (0-59)

1 time field description:

• *: matches any value.
• Numer: specify a specific time.
• ,: indicates multiple time values. For example, 1, 3, 5 means the 1st, 3rd, 5th minute.
• -: indicates the range, for example, 1-5 means from the 1st minute to the 5th minute.
• /: indicates the step size. For example, * / 2 means that it is executed every 2 minutes.

example

# perform a task every 5 minutes
* / 5 * / path/to/command

# perform the task at 8: 00 a.m. every Monday
0 8 * * 1 / path/to/command

# perform tasks at 2: 00 p.m. on the 1st and 15th of each month
0 14 1,15 * * /path/to/command

# perform tasks every hour from 9: 00 a.m. to 5: 00 p.m. Every working day
0 9-17 * 1-5 / path/to/command

2. Special time string