CRON(8) | System Manager's Manual | CRON(8) |
cron
— daemon to
execute scheduled commands (Vixie Cron)
cron |
[-s ] [-o ]
[-x
debugflag[,...]] |
The cron
utility is launched by
launchd(8) when it sees the existence
of /etc/crontab or files in
/usr/lib/cron/tabs. There should be no need to start
it manually. See
/System/Library/LaunchDaemons/com.vix.cron.plist for
details.
The cron
utility searches
/usr/lib/cron/tabs for crontab files which are named
after accounts in /etc/passwd; crontabs found are
loaded into memory. The cron
utility also searches
for /etc/crontab which is in a different format (see
crontab(5)).
The cron
utility 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
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 time on all
crontabs 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.
Available options:
-s
The jobs run during the GMT offset changes time as intuitively expected. If a job falls into a time interval that disappears (for example, during the switch from standard time) to daylight saving time or is duplicated (for example, during the reverse switch), then it is handled in one of two ways:
The first case is for the jobs that run every at hour of a time interval overlapping with the disappearing or duplicated interval. In other words, if the job had run within one hour before the GMT offset change (and cron was not restarted nor the crontab(5) changed after that) or would run after the change at the next hour. They work as always, skip the skipped time or run in the added time as usual.
The second case is for the jobs that run less frequently. They are executed exactly once, they are not skipped nor executed twice (unless cron is restarted or the user's crontab(5) is changed during such a time interval). If an interval disappears due to the GMT offset change, such jobs are executed at the same absolute point of time as they would be in the old time zone. For example, if exactly one hour disappears, this point would be during the next hour at the first minute that is specified for them in crontab(5).
-o
-o
and -s
are specified, the option specified last wins.-x
debugflag[,...]bit
ext
load
misc
pars
proc
sch
test
crontab(1), launchctl(1), crontab(5), launchd.plist(5), launchd(8)
Paul Vixie ⟨paul@vix.com⟩
June 17, 2007 | macOS 14.6 |