CRON(8) BSD System Manager's Manual CRON(8)NAMEcron - daemon to execute scheduled commands (Vixie Cron)
SYNOPSIScronDESCRIPTION
The cron program should be started from /etc/rc or /etc/rc.local. It
will return immediately, so you don't need to start it with ``&''.
The cron program searches /var/cron/tabs for crontab files that are named
after user accounts; these are loaded into memory. It also reads
/etc/crontab, which is in a different format (see crontab(5)). The cron
program then wakes up every minute, examining all stored crontabs, check-
ing 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 environment variable in the crontab, if
such exists).
Additionally, cron checks each minute to see if its spool directory's
modification time (or the modification time on /etc/crontab) has changed,
and if it has, cron will then examine the modification times on all
crontab files and reload those which have changed. Thus cron need not be
restarted whenever a crontab file is modified. Note that the crontab(1)
command updates the modification time of the spool directory whenever it
changes a crontab file.
DIAGNOSTICS
Diagnostic messages are logged via syslog(3). Most describe temporary
system resource allocation failures. If a file in /var/cron/tabs does
not correspond to a valid user name, its name is logged as an ``orphan''.
BUGS
The utility will behave mysteriously if a system clock is reset backward
by more than 59 seconds. Smaller steps, or steps forward, are handled
correctly.
SEE ALSOcrontab(1), setusercontext(3), crontab(5)AUTHOR
Paul Vixie <paul@vix.com>
4.4BSD January 10, 1996 1
