Defining user crontabs (scheduled tasks) on UNIX systems

22 Feb 2009 0 Comments

UNIX’s cron service runs scheduled tasks at dates and times defined by users in crontab files. A user can check their crontab entries from the command line by entering:

crontab -l

… or check another user’s crontab by entering:

sudo crontab -u {username} -l

Crontabs entries are defined as follows:

{minute (*-0-59)} {hour (*-0-23)} {monthday (*-1-31)}
  {month (*-1-12)} {weekday (*-0-7)} {path} {script}

For example, to execute a script once an hour on Mondays, you would use:

0 * * * 1 /usr/bin/php5 the_script.php

To override crontab settings, edit a crontab with either one of these commands:

crontab -e
 
sudo crontab -u {username} -e

… or create a text file containing cron entries:

0,30 *   * * *   /usr/bin/php5 /home/willem/something.php
0    23  * * 0,3 sh /home/willem/cronscripts/run_backup.sh
0    */2 * * *   /usr/bin/php5 /var/www/geekology/sitemap.php

If you created a text file, load it to your or another user’s crontab by entering:

crontab {path_to_text_file}
 
sudo crontab -u {username} {path_to_text_file}

 

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  2. Sending Tweets from the command line using a Bash script
  3. Testing SMTP servers from a UNIX command line
  4. Darkstat: UNIX Packet-sniffing daemon
  5. Change the OS X Network Location from the command line or an AppleScript application
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