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
61 then wakes up every minute, examining all stored crontabs, checking each
62 command to see if it should be run in the current minute.
63 Before running a command from a per-account crontab file,
65 checks the status of the account with
67 and skips the command if the account is unavailable,
68 e.g., locked out or expired.
73 commands, any output is mailed to the owner of the crontab (or to the user
76 environment variable in the crontab, if such exists).
80 checks each minute to see if its spool directory's modification time (or
81 the modification time on
83 has changed, and if it has,
85 will then examine the modification time on all crontabs and reload those
89 need not be restarted whenever a crontab file is modified.
92 command updates the modification time of the spool directory whenever it
96 .Bl -tag -width indent
99 Prior to executing commands,
101 will sleep a random number of seconds in the range from 0 to
103 This will not affect superuser jobs (see
107 must be between 0 and 60 inclusive.
108 Default is 0, which effectively disables time jitter.
110 This option can help to smooth down system load spikes during
111 moments when a lot of jobs are likely to start at once, e.g.,
112 at the beginning of the first minute of each hour.
113 .It Fl J Ar rootjitter
114 Enable time jitter for superuser jobs.
117 except that it will affect jobs run by the superuser only.
119 Overrides the default recipient for
126 explicitly set will send mail to the
129 Sending mail will be disabled by default if
131 set to a null string, usually specified in a shell as
136 Enable special handling of situations when the GMT offset of the local
137 timezone changes, such as the switches between the standard time and
138 daylight saving time.
140 The jobs run during the GMT offset changes time as
141 intuitively expected.
142 If a job falls into a time interval that disappears
143 (for example, during the switch from
144 standard time) to daylight saving time or is
145 duplicated (for example, during the reverse switch), then it is handled
148 The first case is for the jobs that run every at hour of a time interval
149 overlapping with the disappearing or duplicated interval.
150 In other words, if the job had run within one hour before the GMT offset change
151 (and cron was not restarted nor the
154 or would run after the change at the next hour.
155 They work as always, skip the skipped time or run in the added
158 The second case is for the jobs that run less frequently.
159 They are executed exactly once, they are not skipped nor
160 executed twice (unless cron is restarted or the user's
162 is changed during such a time interval).
163 If an interval disappears
164 due to the GMT offset change, such jobs are
165 executed at the same absolute point of time as they would be in the
167 For example, if exactly one hour disappears, this
168 point would be during the next hour at the first minute that is
169 specified for them in
172 Disable the special handling of situations when the GMT offset of the local
173 timezone changes, to be compatible with the old (default) behavior.
178 are specified, the option specified last wins.
179 .It Fl x Ar debugflag Ns Op , Ns Ar ...
180 Enable writing of debugging information to standard output.
181 One or more of the following comma separated
183 identifiers must be specified:
185 .Bl -tag -width ".Cm proc" -compact
189 make the other debug flags more verbose
191 be verbose when loading crontab files
193 be verbose about miscellaneous one-off events
195 be verbose about parsing individual crontab lines
197 be verbose about the state of the process, including all of its offspring
199 be verbose when iterating through the scheduling algorithms
201 trace through the execution, but do not perform any actions
205 .Bl -tag -width /etc/pam.d/cron -compact
208 .It Pa /etc/pam.d/cron
210 configuration file for
212 .It Pa /var/cron/tabs
213 Directory for personal crontab files
221 .An Paul Vixie Aq paul@vix.com