Same as -r, but gives the user a yes/no confirmation prompt before removing the crontab. Note: using su to switch users can confuse crontab, so if you are running it inside of su, always use the -u option to avoid ambiguity.Įdit the current crontab, using the editor specified in the environment variable VISUAL or EDITOR. If this option is not given, crontab opens the crontab of the user who ran crontab. Specifies the user whose crontab is to be viewed or modified. If file is a dash (' -'), the crontab data is read from standard input. Load the crontab data from the specified file. To have this script run every five minutes and notify you via e-mail for any sites that are down, add the crontab job: */5 * * * * /usr/bin/php /home/myuser/check_sites.Syntax crontab file crontab Options file Simply modify the e-mail address and desired URLs to check at the top of the file, and save it somewhere such as /home/myuser/check_sites.php. $status = curl_getinfo($ch, CURLINFO_HTTP_CODE)

Mail($email, 'Urgent - Sites Down!', 'Your bot has detected the following sites are currently down:Ĭurl_setopt($ch, CURLOPT_FRESH_CONNECT, true) Ĭurl_setopt($ch, CURLOPT_RETURNTRANSFER, true) Ĭurl_setopt($ch, CURLOPT_FOLLOWLOCATION, true) Here's a nifty little PHP script that will do just that.

Maybe you want to automatically check every five minutes whether or not various sites are online, and be notified via email if any are down. The above command simply lists all jobs currently in your crontab file, prints the new job, and pipes everything into crontab replacing its contents. You can add the job to your crontab file with the single command: (crontab -l echo '0 14 * * 0 /path/to/command.sh' ) | crontab For example, if you want to add this crontab job that runs every Sunday at 2:00pm: 0 14 * * 0 /path/to/command.sh Instead of manually modifying the crontab file, there is a quick single command you can run to add a job. Once done, save and close the file by pressing Ctrl+W, followed by the Y and Enter keys, which will immediately activate all crontab jobs within the file. Each crontab job resides on one line, and you may add, modify and remove lines as desired. This will open a text editor such as nano with the contents of your crontab file. Run this command in the terminal: crontab -e Generally, the most used method to add or modify crontab jobs is the crontab -e command.

For example: 0 6 15 * * /path/to/backup.sh > /dev/null 2>&1

You may do this by appending > /dev/null 2>&1 to any crontab job. However, if you want to execute the crontab job at specific intervals within a time period you can use */PERIOD, and the below crontab job will automatically execute at 15 minutes past the hour every three hours: 15 */3 * * * /path/to/command.sh Keeping Crontab Jobs QuietĪll depending, you may want to eliminate all output from the crontab jobs so they don't end up in your system's mail folder. You may specify the exact values by separating them with a comma, and the below crontab job will execute every hour at 20 and 50 minutes past the hour: 20,50 * * * * /path/to/command.sh For example, the below crontab job will execute every night at exactly 3:20am: 20 3 * * * /root/backup.sh Multiple ValuesĮach time period may also include multiple elements. You may use an asterisk (*) in any of the fields to denote a wildcard, meaning the crontab job will execute regardless of that time period. The day of the week to execute the crontab job at.Īny Linux command that you can execute on the terminal. The day of the month to execute the crontab job at. The minute to execute the crontab job at. The below table explains the different elements of the crontab job: Element Every crontab job consists of one line, and is formatted as below: MINUTE HOUR DAY MONTH WEEKDAY COMMAND

Crontab editor commands