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 1.25 2007/06/17 17:25:53 yar Exp $
19 .\" $DragonFly: src/usr.sbin/cron/cron/cron.8,v 1.5 2008/01/08 20:30:57 swildner Exp $
26 .Nd daemon to execute scheduled commands (Vixie Cron)
30 .Op Fl J Ar rootjitter
33 .Op Fl x Ar debugflag Ns Op , Ns Ar ...
37 utility should be started from
41 It will return immediately,
42 so you don't need to start it with '&'.
48 for crontab files which are named after accounts in
50 crontabs found are loaded into memory.
53 utility also searches for
55 which is in a different format (see
61 then wakes up every minute, examining all stored crontabs, checking each
62 command to see if it should be run in the current minute.
63 Before running a command from a per-account crontab file,
65 checks the status of the account with
67 and skips the command if the account is unavailable,
68 e.g., locked out or expired.
73 commands, any output is mailed to the owner of the crontab (or to the user
76 environment variable in the crontab, if such exists).
80 checks each minute to see if its spool directory's modification time (or
81 the modification time on
83 has changed, and if it has,
85 will then examine the modification time on all crontabs and reload those
86 which have changed. Thus
88 need not be restarted whenever a crontab file is modified. Note that the
90 command updates the modification time of the spool directory whenever it
94 .Bl -tag -width indent
97 Prior to executing commands,
99 will sleep a random number of seconds in the range from 0 to
101 This won't affect superuser jobs (see
105 must be between 0 and 60 inclusive.
106 Default is 0, which effectively disables time jitter.
108 This option can help to smooth down system load spikes during
109 moments when a lot of jobs are likely to start at once, e.g.,
110 at the beginning of the first minute of each hour.
111 .It Fl J Ar rootjitter
112 Enable time jitter for superuser jobs.
115 except that it will affect jobs run by the superuser only.
117 Enable special handling of situations when the GMT offset of the local
118 timezone changes, such as the switches between the standard time and
119 daylight saving time.
121 The jobs run during the GMT offset changes time as
122 intuitively expected.
123 If a job falls into a time interval that disappears
124 (for example, during the switch from
125 standard time) to daylight saving time or is
126 duplicated (for example, during the reverse switch), then it's handled
129 The first case is for the jobs that run every at hour of a time interval
130 overlapping with the disappearing or duplicated interval.
131 In other words, if the job had run within one hour before the GMT offset change
132 (and cron was not restarted nor the
135 or would run after the change at the next hour.
136 They work as always, skip the skipped time or run in the added
139 The second case is for the jobs that run less frequently.
140 They are executed exactly once, they are not skipped nor
141 executed twice (unless cron is restarted or the user's
143 is changed during such a time interval).
144 If an interval disappears
145 due to the GMT offset change, such jobs are
146 executed at the same absolute point of time as they would be in the
148 For example, if exactly one hour disappears, this
149 point would be during the next hour at the first minute that is
150 specified for them in
153 Disable the special handling of situations when the GMT offset of the local
154 timezone changes, to be compatible with the old (default) behavior.
159 are specified, the option specified last wins.
160 .It Fl x Ar debugflag Ns Op , Ns Ar ...
161 Enable writing of debugging information to standard output.
162 One or more of the following comma separated
164 identifiers must be specified:
166 .Bl -tag -width ".Cm proc" -compact
170 make the other debug flags more verbose
172 be verbose when loading crontab files
174 be verbose about miscellaneous one-off events
176 be verbose about parsing individual crontab lines
178 be verbose about the state of the process, including all of its offspring
180 be verbose when iterating through the scheduling algorithms
182 trace through the execution, but do not perform any actions
186 .Bl -tag -width /etc/pam.d/cron -compact
189 .It Pa /etc/pam.d/cron
191 configuration file for
193 .It Pa /var/cron/tabs
194 Directory for personal crontab files
202 .An Paul Vixie Aq paul@vix.com