1 .\"/* Copyright 1988,1990,1993 by Paul Vixie
2 .\" * All rights reserved
4 .\" * Distribute freely, except: don't remove my name from the source or
5 .\" * documentation (don't take credit for my work), mark your changes (don't
6 .\" * get me blamed for your possible bugs), don't alter or remove this
7 .\" * notice. May be sold if buildable source is provided to buyer. No
8 .\" * warrantee of any kind, express or implied, is included with this
9 .\" * software; use at your own risk, responsibility for damages (if any) to
10 .\" * anyone resulting from the use of this software rests entirely with the
13 .\" * Send bug reports, bug fixes, enhancements, requests, flames, etc., and
14 .\" * I'll try to keep a version up to date. I can be reached as follows:
15 .\" * Paul Vixie <paul@vix.com> uunet!decwrl!vixie!paul
18 .\" $FreeBSD: src/usr.sbin/cron/cron/cron.8,v 1.7.2.9 2003/03/11 21:13:48 trhodes Exp $
19 .\" $DragonFly: src/usr.sbin/cron/cron/cron.8,v 1.2 2003/06/17 04:29:53 dillon Exp $
26 .Nd daemon to execute scheduled commands (Vixie Cron)
31 .Op Fl x Ar debugflag Ns Op , Ns Ar ...
35 utility should be started from
39 It will return immediately,
40 so you don't need to start it with '&'.
46 for crontab files which are named after accounts in
48 crontabs found are loaded into memory.
51 utility also searches for
53 which is in a different format (see
58 then wakes up every minute, examining all stored crontabs, checking each
59 command to see if it should be run in the current minute. When executing
60 commands, any output is mailed to the owner of the crontab (or to the user
63 environment variable in the crontab, if such exists).
67 checks each minute to see if its spool directory's modification time (or
68 the modification time on
70 has changed, and if it has,
72 will then examine the modification time on all crontabs and reload those
73 which have changed. Thus
75 need not be restarted whenever a crontab file is modified. Note that the
77 command updates the modification time of the spool directory whenever it
81 .Bl -tag -width indent
83 Enable special handling of situations when the GMT offset of the local
84 timezone changes, such as the switches between the standard time and
87 The jobs run during the GMT offset changes time as
89 If a job falls into a time interval that disappears
90 (for example, during the switch from
91 standard time) to daylight saving time or is
92 duplicated (for example, during the reverse switch), then it's handled
95 The first case is for the jobs that run every at hour of a time interval
96 overlapping with the disappearing or duplicated interval.
97 In other words, if the job had run within one hour before the GMT offset change
98 (and cron was not restarted nor the
101 or would run after the change at the next hour.
102 They work as always, skip the skipped time or run in the added
105 The second case is for the jobs that run less frequently.
106 They are executed exactly once, they are not skipped nor
107 executed twice (unless cron is restarted or the user's
109 is changed during such a time interval).
110 If an interval disappears
111 due to the GMT offset change, such jobs are
112 executed at the same absolute point of time as they would be in the
114 For example, if exactly one hour disappears, this
115 point would be during the next hour at the first minute that is
116 specified for them in
119 Disable the special handling of situations when the GMT offset of the local
120 timezone changes, to be compatible with the old (default) behavior.
125 are specified, the option specified last wins.
126 .It Fl x Ar debugflag Ns Op , Ns Ar ...
127 Enable writing of debugging information to standard output.
128 One or more of the following comma separated
130 identifiers must be specified:
132 .Bl -tag -width ".Cm proc" -compact
136 make the other debug flags more verbose
138 be verbose when loading crontab files
140 be verbose about miscellaneous one-off events
142 be verbose about parsing individual crontab lines
144 be verbose about the state of the process, including all of its offspring
146 be verbose when iterating through the scheduling algorithms
148 trace through the execution, but do not perform any actions
155 .An Paul Vixie Aq paul@vix.com