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).
82 The from address of this mail may be set with the
88 checks each minute to see if its spool directory's modification time (or
89 the modification time on
91 has changed, and if it has,
93 will then examine the modification time on all crontabs and reload those
97 need not be restarted whenever a crontab file is modified.
100 command updates the modification time of the spool directory whenever it
104 .Bl -tag -width indent
107 Prior to executing commands,
109 will sleep a random number of seconds in the range from 0 to
111 This will not affect superuser jobs (see
115 must be between 0 and 60 inclusive.
116 Default is 0, which effectively disables time jitter.
118 This option can help to smooth down system load spikes during
119 moments when a lot of jobs are likely to start at once, e.g.,
120 at the beginning of the first minute of each hour.
121 .It Fl J Ar rootjitter
122 Enable time jitter for superuser jobs.
125 except that it will affect jobs run by the superuser only.
127 Overrides the default recipient for
134 explicitly set will send mail to the
137 Sending mail will be disabled by default if
139 set to a null string, usually specified in a shell as
144 Do not daemonize; run in foreground instead.
146 Enable special handling of situations when the GMT offset of the local
147 timezone changes, such as the switches between the standard time and
148 daylight saving time.
150 The jobs run during the GMT offset changes time as
151 intuitively expected.
152 If a job falls into a time interval that disappears
153 (for example, during the switch from
154 standard time) to daylight saving time or is
155 duplicated (for example, during the reverse switch), then it is handled
158 The first case is for the jobs that run every at hour of a time interval
159 overlapping with the disappearing or duplicated interval.
160 In other words, if the job had run within one hour before the GMT offset change
161 (and cron was not restarted nor the
164 or would run after the change at the next hour.
165 They work as always, skip the skipped time or run in the added
168 The second case is for the jobs that run less frequently.
169 They are executed exactly once, they are not skipped nor
170 executed twice (unless cron is restarted or the user's
172 is changed during such a time interval).
173 If an interval disappears
174 due to the GMT offset change, such jobs are
175 executed at the same absolute point of time as they would be in the
177 For example, if exactly one hour disappears, this
178 point would be during the next hour at the first minute that is
179 specified for them in
182 Disable the special handling of situations when the GMT offset of the local
183 timezone changes, to be compatible with the old (default) behavior.
188 are specified, the option specified last wins.
189 .It Fl x Ar debugflag Ns Op , Ns Ar ...
190 Enable writing of debugging information to standard output.
191 One or more of the following comma separated
193 identifiers must be specified:
195 .Bl -tag -width ".Cm proc" -compact
199 make the other debug flags more verbose
201 be verbose when loading crontab files
203 be verbose about miscellaneous one-off events
205 be verbose about parsing individual crontab lines
207 be verbose about the state of the process, including all of its offspring
209 be verbose when iterating through the scheduling algorithms
211 trace through the execution, but do not perform any actions
215 .Bl -tag -width /usr/local/etc/cron.d -compact
219 Directory for optional/modularized system crontab files.
220 .It Pa /etc/pam.d/cron
222 configuration file for
224 .It Pa /usr/local/etc/cron.d
225 Directory for third-party package provided crontab files.
226 .It Pa /var/cron/tabs
227 Directory for personal crontab files
235 .An Paul Vixie Aq Mt paul@vix.com