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 $
25 .Nd daemon to execute scheduled commands (Vixie Cron)
30 .Op Fl x Ar debugflag Ns Op , Ns Ar ...
34 utility should be started from
38 It will return immediately,
39 so you don't need to start it with '&'.
45 for crontab files which are named after accounts in
47 crontabs found are loaded into memory.
50 utility also searches for
52 which is in a different format (see
57 then wakes up every minute, examining all stored crontabs, checking each
58 command to see if it should be run in the current minute. When executing
59 commands, any output is mailed to the owner of the crontab (or to the user
62 environment variable in the crontab, if such exists).
66 checks each minute to see if its spool directory's modification time (or
67 the modification time on
69 has changed, and if it has,
71 will then examine the modification time on all crontabs and reload those
72 which have changed. Thus
74 need not be restarted whenever a crontab file is modified. Note that the
76 command updates the modification time of the spool directory whenever it
80 .Bl -tag -width indent
82 Enable special handling of situations when the GMT offset of the local
83 timezone changes, such as the switches between the standard time and
86 The jobs run during the GMT offset changes time as
88 If a job falls into a time interval that disappears
89 (for example, during the switch from
90 standard time) to daylight saving time or is
91 duplicated (for example, during the reverse switch), then it's handled
94 The first case is for the jobs that run every at hour of a time interval
95 overlapping with the disappearing or duplicated interval.
96 In other words, if the job had run within one hour before the GMT offset change
97 (and cron was not restarted nor the
100 or would run after the change at the next hour.
101 They work as always, skip the skipped time or run in the added
104 The second case is for the jobs that run less frequently.
105 They are executed exactly once, they are not skipped nor
106 executed twice (unless cron is restarted or the user's
108 is changed during such a time interval).
109 If an interval disappears
110 due to the GMT offset change, such jobs are
111 executed at the same absolute point of time as they would be in the
113 For example, if exactly one hour disappears, this
114 point would be during the next hour at the first minute that is
115 specified for them in
118 Disable the special handling of situations when the GMT offset of the local
119 timezone changes, to be compatible with the old (default) behavior.
124 are specified, the option specified last wins.
125 .It Fl x Ar debugflag Ns Op , Ns Ar ...
126 Enable writing of debugging information to standard output.
127 One or more of the following comma separated
129 identifiers must be specified:
131 .Bl -tag -width ".Cm proc" -compact
135 make the other debug flags more verbose
137 be verbose when loading crontab files
139 be verbose about miscellaneous one-off events
141 be verbose about parsing individual crontab lines
143 be verbose about the state of the process, including all of its offspring
145 be verbose when iterating through the scheduling algorithms
147 trace through the execution, but do not perform any actions
154 .An Paul Vixie Aq paul@vix.com