CRON(8) BSD System Manager's Manual CRON(8)
NAME
ccrroonn - daemon to execute scheduled commands (Vixie Cron)
SYNOPSIS
ccrroonn [-ss] [-oo] [-xx debugflag[,...]]
DESCRIPTION
The ccrroonn 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 ccrroonn utility searches /usr/lib/cron/tabs for crontab files which are
named after accounts in /etc/passwd; crontabs found are loaded into mem-
ory. The ccrroonn utility also searches for /etc/crontab which is in a dif-
ferent format (see crontab(5)). The ccrroonn 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, ccrroonn 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, ccrroonn will then examine the modification time on all
crontabs and reload those which have changed. Thus ccrroonn 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:
-oo Disable the special handling of situations when the GMT offset of
the local timezone changes, to be compatible with the old
(default) behavior. If both options -oo and -ss are specified, the
option specified last wins.
-ss Enable special handling of situations when the GMT offset of the
local timezone changes, such as the switches between the standard
time and daylight saving time.
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 at every hour of a time
interval, overlapping with the disappearing or duplicated inter-
val. 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, skipping the skipped time or
running in the added time, as usual.
The second case is for the jobs that run less frequently. These
are executed exactly once; they are neither 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).
-xx debugflag[,...]
Enable writing of debugging information to standard output. One
or more of the following comma-separated debugflag identifiers
must be specified:
bbiitt currently not used
eexxtt make the other debug flags more verbose
llooaadd be verbose when loading crontab files
mmiisscc be verbose about miscellaneous one-off events
ppaarrss be verbose about parsing individual crontab lines
pprroocc be verbose about the state of the process, including all of
its offspring
sscchh be verbose when iterating through the scheduling algorithms
tteesstt trace through the execution, but do not perform any actions
SEE ALSO
crontab(1), launchctl(1), crontab(5), launchd.plist(5), launchd(8)
AUTHORS Paul Vixie
BSD December 20, 1993 BSD