crontab syntax cheat sheet: * * * * * explained

A crontab line has five time fields followed by the command: minute hour day-of-month month day-of-week command. * means "every value", so * * * * * runs every minute and 30 2 * * 1 runs at 02:30 every Monday. Edit your table with crontab -e, list it with crontab -l.

The five fields

When both day of month and day of week are restricted (not *), the job runs when either matches: 0 0 1 * 1 runs on the 1st of the month and on every Monday.

Operators

Ranges, lists and steps are supported by cronie and Vixie cron; strict POSIX crontab only defines lists and ranges.

Common schedules

*/5 * * * *     every 5 minutes
0 * * * *       every hour, on the hour
0 0 * * *       every day at midnight
30 2 * * *      every day at 02:30
0 9 * * 1-5     weekdays at 09:00
0 0 * * 0       every Sunday at midnight
0 0 1 * *       the first day of every month
0 0 1 1 *       once a year, January 1st

Special strings

Managing the table

crontab -e             # edit your crontab (opens $EDITOR)
crontab -l             # print it
crontab -l > cron.bak  # back it up
crontab cron.bak       # replace it with the contents of a file
crontab -u alice -l    # another user's table (root only)

Gotchas

• Jobs run with a minimal environment: PATH is usually /usr/bin:/bin, and your shell profile is not read. Use absolute paths or set PATH= at the top of the crontab.
• % in the command is turned into a newline; escape it as \% (for example in date +\%F).
• Output is mailed to the user if a mail transfer agent exists; otherwise it may be lost. Redirect it: >> /var/log/job.log 2>&1.
• System crontabs (/etc/crontab, /etc/cron.d/*) have an extra user field between the time fields and the command.
• The schedule uses the time zone of the cron daemon. cronie supports CRON_TZ= in the table to change it for the following lines.