Free Software Server Environment: cron crond crontab

http://linux.die.net/man/1/crontab∞
http://linux.die.net/man/5/crontab∞
http://linux.die.net/man/8/crond∞

cron crond crontab

cron crond crontab are used as the system scheduler

Your cron jobs

# crontab -l | cut -c -70

System cron jobs

# cat /etc/crontab

Everyones cron jobs

#ls -lR /var/spool/cron/

Edit Jobs

# crontab -e

crontab file format

cron jobs run a maximum of once a minute

min hour day month day-of-week command # comment

you can use * to indicate every min/hour/day
you can use - to indicate ranges
you can use / to indicate intervals
examples

$ crontab -l

* * * * * pwd            #every min of every day
*/10 9-17 * * 1-5 pwd             # every 10 mins between 9am - 5pm on monday - friday

cron emails

By default cron emails commands output to 'cron' user so if you want email sent elsewhere you have to specify it and prevent any output using STDERR OutputRedirection (2>&1) (or >& if you also specifing a specific destination)

$ crontab -l

10 * * * 1-5 pwd 2>&1 | smtp=upstream /usr/local/bin/mailx -s "<subject>" <diffuser@diffdomain>

SystemDefaultCronTab

REFERRERS
SystemServices