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
25 .Nd daemon to execute scheduled commands (Vixie Cron)
29 .Op Fl J Ar rootjitter
34 .Op Fl x Ar debugflag Ns Op , Ns Ar ...
38 utility should be started from
42 It will return immediately,
43 so you do not need to start it with '&'.
49 for crontab files which are named after accounts in
51 crontabs found are loaded into memory.
54 utility also searches for
59 .Pa /usr/local/etc/cron.d
60 which are in a different format (see
66 then wakes up every minute, examining all stored crontabs, checking each
67 command to see if it should be run in the current minute.
68 Before running a command from a per-account crontab file,
70 checks the status of the account with
72 and skips the command if the account is unavailable,
73 e.g., locked out or expired.
78 commands, any output is mailed to the owner of the crontab (or to the user
81 environment variable in the crontab, if such exists).
85 checks each minute to see if its spool directory's modification time (or
86 the modification time on
88 has changed, and if it has,
90 will then examine the modification time on all crontabs and reload those
94 need not be restarted whenever a crontab file is modified.
97 command updates the modification time of the spool directory whenever it
101 .Bl -tag -width indent
104 Prior to executing commands,
106 will sleep a random number of seconds in the range from 0 to
108 This will not affect superuser jobs (see
112 must be between 0 and 60 inclusive.
113 Default is 0, which effectively disables time jitter.
115 This option can help to smooth down system load spikes during
116 moments when a lot of jobs are likely to start at once, e.g.,
117 at the beginning of the first minute of each hour.
118 .It Fl J Ar rootjitter
119 Enable time jitter for superuser jobs.
122 except that it will affect jobs run by the superuser only.
124 Overrides the default recipient for
131 explicitly set will send mail to the
134 Sending mail will be disabled by default if
136 set to a null string, usually specified in a shell as
141 Do not daemonize; run in foreground instead.
143 Enable special handling of situations when the GMT offset of the local
144 timezone changes, such as the switches between the standard time and
145 daylight saving time.
147 The jobs run during the GMT offset changes time as
148 intuitively expected.
149 If a job falls into a time interval that disappears
150 (for example, during the switch from
151 standard time) to daylight saving time or is
152 duplicated (for example, during the reverse switch), then it is handled
155 The first case is for the jobs that run every at hour of a time interval
156 overlapping with the disappearing or duplicated interval.
157 In other words, if the job had run within one hour before the GMT offset change
158 (and cron was not restarted nor the
161 or would run after the change at the next hour.
162 They work as always, skip the skipped time or run in the added
165 The second case is for the jobs that run less frequently.
166 They are executed exactly once, they are not skipped nor
167 executed twice (unless cron is restarted or the user's
169 is changed during such a time interval).
170 If an interval disappears
171 due to the GMT offset change, such jobs are
172 executed at the same absolute point of time as they would be in the
174 For example, if exactly one hour disappears, this
175 point would be during the next hour at the first minute that is
176 specified for them in
179 Disable the special handling of situations when the GMT offset of the local
180 timezone changes, to be compatible with the old (default) behavior.
185 are specified, the option specified last wins.
186 .It Fl x Ar debugflag Ns Op , Ns Ar ...
187 Enable writing of debugging information to standard output.
188 One or more of the following comma separated
190 identifiers must be specified:
192 .Bl -tag -width ".Cm proc" -compact
196 make the other debug flags more verbose
198 be verbose when loading crontab files
200 be verbose about miscellaneous one-off events
202 be verbose about parsing individual crontab lines
204 be verbose about the state of the process, including all of its offspring
206 be verbose when iterating through the scheduling algorithms
208 trace through the execution, but do not perform any actions
212 .Bl -tag -width /usr/local/etc/cron.d -compact
216 Directory for optional/modularized system crontab files.
217 .It Pa /etc/pam.d/cron
219 configuration file for
221 .It Pa /usr/local/etc/cron.d
222 Directory for third-party package provided crontab files.
223 .It Pa /var/cron/tabs
224 Directory for personal crontab files
232 .An Paul Vixie Aq paul@vix.com