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
33 .Op Fl x Ar debugflag Ns Op , Ns Ar ...
37 utility should be started from
41 It will return immediately,
42 so you do not 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
58 .Pa /usr/local/etc/cron.d
59 which are in a different format (see
65 then wakes up every minute, examining all stored crontabs, checking each
66 command to see if it should be run in the current minute.
67 Before running a command from a per-account crontab file,
69 checks the status of the account with
71 and skips the command if the account is unavailable,
72 e.g., locked out or expired.
77 commands, any output is mailed to the owner of the crontab (or to the user
80 environment variable in the crontab, if such exists).
84 checks each minute to see if its spool directory's modification time (or
85 the modification time on
87 has changed, and if it has,
89 will then examine the modification time on all crontabs and reload those
93 need not be restarted whenever a crontab file is modified.
96 command updates the modification time of the spool directory whenever it
100 .Bl -tag -width indent
103 Prior to executing commands,
105 will sleep a random number of seconds in the range from 0 to
107 This will not affect superuser jobs (see
111 must be between 0 and 60 inclusive.
112 Default is 0, which effectively disables time jitter.
114 This option can help to smooth down system load spikes during
115 moments when a lot of jobs are likely to start at once, e.g.,
116 at the beginning of the first minute of each hour.
117 .It Fl J Ar rootjitter
118 Enable time jitter for superuser jobs.
121 except that it will affect jobs run by the superuser only.
123 Overrides the default recipient for
130 explicitly set will send mail to the
133 Sending mail will be disabled by default if
135 set to a null string, usually specified in a shell as
140 Enable special handling of situations when the GMT offset of the local
141 timezone changes, such as the switches between the standard time and
142 daylight saving time.
144 The jobs run during the GMT offset changes time as
145 intuitively expected.
146 If a job falls into a time interval that disappears
147 (for example, during the switch from
148 standard time) to daylight saving time or is
149 duplicated (for example, during the reverse switch), then it is handled
152 The first case is for the jobs that run every at hour of a time interval
153 overlapping with the disappearing or duplicated interval.
154 In other words, if the job had run within one hour before the GMT offset change
155 (and cron was not restarted nor the
158 or would run after the change at the next hour.
159 They work as always, skip the skipped time or run in the added
162 The second case is for the jobs that run less frequently.
163 They are executed exactly once, they are not skipped nor
164 executed twice (unless cron is restarted or the user's
166 is changed during such a time interval).
167 If an interval disappears
168 due to the GMT offset change, such jobs are
169 executed at the same absolute point of time as they would be in the
171 For example, if exactly one hour disappears, this
172 point would be during the next hour at the first minute that is
173 specified for them in
176 Disable the special handling of situations when the GMT offset of the local
177 timezone changes, to be compatible with the old (default) behavior.
182 are specified, the option specified last wins.
183 .It Fl x Ar debugflag Ns Op , Ns Ar ...
184 Enable writing of debugging information to standard output.
185 One or more of the following comma separated
187 identifiers must be specified:
189 .Bl -tag -width ".Cm proc" -compact
193 make the other debug flags more verbose
195 be verbose when loading crontab files
197 be verbose about miscellaneous one-off events
199 be verbose about parsing individual crontab lines
201 be verbose about the state of the process, including all of its offspring
203 be verbose when iterating through the scheduling algorithms
205 trace through the execution, but do not perform any actions
209 .Bl -tag -width /etc/pam.d/cron -compact
212 .It Pa /etc/pam.d/cron
214 configuration file for
216 .It Pa /var/cron/tabs
217 Directory for personal crontab files
225 .An Paul Vixie Aq paul@vix.com