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cron - daemon to execute scheduled commands (Vixie Cron)
Cron should be started from /etc/rc or /etc/rc.local. It will return immediately, so you
don't need to start it with '&'.
Cron searches /var/spool/cron for crontab files which are named after accounts in
/etc/passwd; crontabs found are loaded into memory. Cron also searches for /etc/crontab
and the files in the /etc/cron.d/ directory, which are in a different format (see
crontab(5)). Cron then wakes up every minute, examining all stored crontabs, checking
each command to see if it should be run in the current minute. When executing commands,
any output is mailed to the owner of the crontab (or to the user named in the MAILTO envi-
ronment variable in the crontab, if such exists).
Additionally, cron checks each minute to see if its spool directory's modtime (or the mod-
time on /etc/crontab) has changed, and if it has, cron will then examine the modtime on
all crontabs and reload those which have changed. Thus cron need not be restarted when-
ever a crontab file is modified. Note that the Crontab(1) command updates the modtime of
the spool directory whenever it changes a crontab.
Paul Vixie <email@example.com>
4th Berkeley Distribution 20 December 1993 CRON(8)
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