crontab

   1 crontab -e # edit cron for current user
   2 crontab -l # list cron for current user
   3 

   1 */10 * * * * /path/to/command

   1 0 * * * * /path/to/command

   1 0 */2 * * * /path/to/command

   1 0 0 * * *  /path/to/command

   1 0 8 * * *  /path/to/command

   1 # Order of crontab fields
   2 # minute        hour    mday    month   wday    command
   3 

   1 string         meaning
   2 ------         -------
   3 @reboot        Run once, at startup.
   4 @yearly        Run once a year, "0 0 1 1 *".
   5 @annually      (same as @yearly)
   6 @monthly       Run once a month, "0 0 1 * *".
   7 @weekly        Run once a week, "0 0 * * 0".
   8 @daily         Run once a day, "0 0 * * *".
   9 @midnight      (same as @daily)
  10 @hourly        Run once an hour, "0 * * * *".