Crontab examples for Linux

A Linux crontab line has five time fields (minute, hour, day of month, month, weekday) followed by the command. Crond compares those fields with the server clock once a minute and runs the command when they match. There is no seconds field on a normal user crontab.

The star means every allowed value in that field. A comma lists values, so 8,20 in the hour field is 08:00 and 20:00. A hyphen is a range, so 1-5 in the weekday field is Monday through Friday. A slash is a step: */15 in the minute field is minute 0, 15, 30, and 45.

Month and weekday fields also accept names, such as jan or mon. Sunday is 0 or 7. Monday is 1 and Saturday is 6. The clock is the server clock. If date prints UTC, 02:00 in the crontab is 07:30 IST. cronie, the cron on AlmaLinux, Rocky and Fedora, documents a CRON_TZ=Asia/Kolkata line that makes the entries below it use IST; check man 5 crontab on Debian or Ubuntu before relying on it there.

If both the day-of-month and the weekday are restricted, Vixie cron and cronie run the job when either field matches. The line 0 6 1 * 1 runs at 06:00 on the 1st and also on every Monday. A star in either field turns that rule off.

Those five fields are the same schedule described in what a cron job is. The lines below are the ones you paste.

Daily, weekly and monthly jobs fix the minute and hour, then restrict the weekday or day of month. They use the same five fields. Set the hour and the day, and leave the minute at 0 unless the job needs a different minute.

A backup that only copies files is not a restore test. After the 03:15 job, check that the archive exists and that the disk still has room. The checks for free disk space on a Linux server are the next step when the dump grows every night.

A job does not run late if the server was off at that minute. The next matching minute is the next chance. The @reboot shortcut below is the boot case, not a catch-up for a missed 03:15.

To run WordPress scheduled tasks from real cron, set DISABLE_WP_CRON in wp-config.php and call wp-cron.php from a crontab line every 5 or 15 minutes. By default WordPress only checks its schedule when someone visits, so a quiet site runs scheduled posts and backups late, and a busy one checks on many page loads.

# wp-config.php, above the "stop editing" line
define( 'DISABLE_WP_CRON', true );

# crontab -e
*/15 * * * * /usr/bin/php /home/user/public_html/wp-cron.php >/dev/null 2>&1
# or, with WP-CLI installed:
*/15 * * * * /usr/local/bin/wp cron event run --due-now --path=/home/user/public_html >/dev/null 2>&1

Check the path with command -v wp before pasting the second line. Run either command once by hand first; an error there will also fail in cron.

A crontab job usually fails silently because cron's environment is smaller than your login shell: a short PATH, /bin/sh and no profile. The usual default PATH is /usr/bin:/bin and the usual shell is /bin/sh, not bash.

Find the binary while logged in with command -v php or command -v python3, then paste that path into the crontab. A relative path such as scripts/backup.sh depends on the current directory, which cron does not set to your home in a reliable way.

$HOME is set. A leading tilde is not expanded in every cron. Write /home/user/scripts/backup.sh instead of a short name.

The script must be executable by the user who owns the crontab, and it must use Unix line endings. A permission denied line in the mail is the script or the directory, not the five time fields.

An unescaped percent sign in the command is special. Cron turns the first % into a newline and sends the rest to the command as input. Write date +\%Y-\%m-\%d or the format never reaches date.

A job longer than its gap can start a second copy. flock -n /tmp/backup.lock /home/user/scripts/backup.sh skips the new start while the lock is held.

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