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
32 .Op Fl x Ar debugflag Ns Op , Ns Ar ...
36 utility should be started from
40 It will return immediately,
41 so you don't need to start it with '&'.
47 for crontab files which are named after accounts in
49 crontabs found are loaded into memory.
52 utility also searches for
54 which is in a different format (see
59 then wakes up every minute, examining all stored crontabs, checking each
60 command to see if it should be run in the current minute.
62 commands, any output is mailed to the owner of the crontab (or to the user
65 environment variable in the crontab, if such exists).
69 checks each minute to see if its spool directory's modification time (or
70 the modification time on
72 has changed, and if it has,
74 will then examine the modification time on all crontabs and reload those
78 need not be restarted whenever a crontab file is modified.
81 command updates the modification time of the spool directory whenever it
85 .Bl -tag -width indent
88 Prior to executing commands,
90 will sleep a random number of seconds in the range from 0 to
92 This won't affect superuser jobs (see
96 must be between 0 and 60 inclusive.
97 Default is 0, which effectively disables time jitter.
99 This option can help to smooth down system load spikes during
100 moments when a lot of jobs are likely to start at once, e.g.,
101 at the beginning of the first minute of each hour.
102 .It Fl J Ar rootjitter
103 Enable time jitter for superuser jobs.
106 except that it will affect jobs run by the superuser only.
108 Enable special handling of situations when the GMT offset of the local
109 timezone changes, such as the switches between the standard time and
110 daylight saving time.
112 The jobs run during the GMT offset changes time as
113 intuitively expected.
114 If a job falls into a time interval that disappears
115 (for example, during the switch from
116 standard time) to daylight saving time or is
117 duplicated (for example, during the reverse switch), then it's handled
120 The first case is for the jobs that run every at hour of a time interval
121 overlapping with the disappearing or duplicated interval.
122 In other words, if the job had run within one hour before the GMT offset change
123 (and cron was not restarted nor the
126 or would run after the change at the next hour.
127 They work as always, skip the skipped time or run in the added
130 The second case is for the jobs that run less frequently.
131 They are executed exactly once, they are not skipped nor
132 executed twice (unless cron is restarted or the user's
134 is changed during such a time interval).
135 If an interval disappears
136 due to the GMT offset change, such jobs are
137 executed at the same absolute point of time as they would be in the
139 For example, if exactly one hour disappears, this
140 point would be during the next hour at the first minute that is
141 specified for them in
144 Disable the special handling of situations when the GMT offset of the local
145 timezone changes, to be compatible with the old (default) behavior.
150 are specified, the option specified last wins.
151 .It Fl x Ar debugflag Ns Op , Ns Ar ...
152 Enable writing of debugging information to standard output.
153 One or more of the following comma separated
155 identifiers must be specified:
157 .Bl -tag -width ".Cm proc" -compact
161 make the other debug flags more verbose
163 be verbose when loading crontab files
165 be verbose about miscellaneous one-off events
167 be verbose about parsing individual crontab lines
169 be verbose about the state of the process, including all of its offspring
171 be verbose when iterating through the scheduling algorithms
173 trace through the execution, but do not perform any actions
180 .An Paul Vixie Aq paul@vix.com