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
55 which is in a different format (see
60 then wakes up every minute, examining all stored crontabs, checking each
61 command to see if it should be run in the current minute.
63 commands, any output is mailed to the owner of the crontab (or to the user
66 environment variable in the crontab, if such exists).
70 checks each minute to see if its spool directory's modification time (or
71 the modification time on
73 has changed, and if it has,
75 will then examine the modification time on all crontabs and reload those
79 need not be restarted whenever a crontab file is modified.
82 command updates the modification time of the spool directory whenever it
86 .Bl -tag -width indent
89 Prior to executing commands,
91 will sleep a random number of seconds in the range from 0 to
93 This will not affect superuser jobs (see
97 must be between 0 and 60 inclusive.
98 Default is 0, which effectively disables time jitter.
100 This option can help to smooth down system load spikes during
101 moments when a lot of jobs are likely to start at once, e.g.,
102 at the beginning of the first minute of each hour.
103 .It Fl J Ar rootjitter
104 Enable time jitter for superuser jobs.
107 except that it will affect jobs run by the superuser only.
109 Overrides the default recipient for
116 explicitly set will send mail to the
119 Sending mail will be disabled by default if
121 set to a null string, usually specified in a shell as
126 Enable special handling of situations when the GMT offset of the local
127 timezone changes, such as the switches between the standard time and
128 daylight saving time.
130 The jobs run during the GMT offset changes time as
131 intuitively expected.
132 If a job falls into a time interval that disappears
133 (for example, during the switch from
134 standard time) to daylight saving time or is
135 duplicated (for example, during the reverse switch), then it is handled
138 The first case is for the jobs that run every at hour of a time interval
139 overlapping with the disappearing or duplicated interval.
140 In other words, if the job had run within one hour before the GMT offset change
141 (and cron was not restarted nor the
144 or would run after the change at the next hour.
145 They work as always, skip the skipped time or run in the added
148 The second case is for the jobs that run less frequently.
149 They are executed exactly once, they are not skipped nor
150 executed twice (unless cron is restarted or the user's
152 is changed during such a time interval).
153 If an interval disappears
154 due to the GMT offset change, such jobs are
155 executed at the same absolute point of time as they would be in the
157 For example, if exactly one hour disappears, this
158 point would be during the next hour at the first minute that is
159 specified for them in
162 Disable the special handling of situations when the GMT offset of the local
163 timezone changes, to be compatible with the old (default) behavior.
168 are specified, the option specified last wins.
169 .It Fl x Ar debugflag Ns Op , Ns Ar ...
170 Enable writing of debugging information to standard output.
171 One or more of the following comma separated
173 identifiers must be specified:
175 .Bl -tag -width ".Cm proc" -compact
179 make the other debug flags more verbose
181 be verbose when loading crontab files
183 be verbose about miscellaneous one-off events
185 be verbose about parsing individual crontab lines
187 be verbose about the state of the process, including all of its offspring
189 be verbose when iterating through the scheduling algorithms
191 trace through the execution, but do not perform any actions
198 .An Paul Vixie Aq paul@vix.com