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
56 which is in a different format (see
62 then wakes up every minute, examining all stored crontabs, checking each
63 command to see if it should be run in the current minute.
64 Before running a command from a per-account crontab file,
66 checks the status of the account with
68 and skips the command if the account is unavailable,
69 e.g., locked out or expired.
74 commands, any output is mailed to the owner of the crontab (or to the user
77 environment variable in the crontab, if such exists).
81 checks each minute to see if its spool directory's modification time (or
82 the modification time on
84 has changed, and if it has,
86 will then examine the modification time on all crontabs and reload those
90 need not be restarted whenever a crontab file is modified.
93 command updates the modification time of the spool directory whenever it
97 .Bl -tag -width indent
100 Prior to executing commands,
102 will sleep a random number of seconds in the range from 0 to
104 This will not affect superuser jobs (see
108 must be between 0 and 60 inclusive.
109 Default is 0, which effectively disables time jitter.
111 This option can help to smooth down system load spikes during
112 moments when a lot of jobs are likely to start at once, e.g.,
113 at the beginning of the first minute of each hour.
114 .It Fl J Ar rootjitter
115 Enable time jitter for superuser jobs.
118 except that it will affect jobs run by the superuser only.
120 Overrides the default recipient for
127 explicitly set will send mail to the
130 Sending mail will be disabled by default if
132 set to a null string, usually specified in a shell as
137 Don't daemonize, run in foreground instead.
139 Enable special handling of situations when the GMT offset of the local
140 timezone changes, such as the switches between the standard time and
141 daylight saving time.
143 The jobs run during the GMT offset changes time as
144 intuitively expected.
145 If a job falls into a time interval that disappears
146 (for example, during the switch from
147 standard time) to daylight saving time or is
148 duplicated (for example, during the reverse switch), then it is handled
151 The first case is for the jobs that run every at hour of a time interval
152 overlapping with the disappearing or duplicated interval.
153 In other words, if the job had run within one hour before the GMT offset change
154 (and cron was not restarted nor the
157 or would run after the change at the next hour.
158 They work as always, skip the skipped time or run in the added
161 The second case is for the jobs that run less frequently.
162 They are executed exactly once, they are not skipped nor
163 executed twice (unless cron is restarted or the user's
165 is changed during such a time interval).
166 If an interval disappears
167 due to the GMT offset change, such jobs are
168 executed at the same absolute point of time as they would be in the
170 For example, if exactly one hour disappears, this
171 point would be during the next hour at the first minute that is
172 specified for them in
175 Disable the special handling of situations when the GMT offset of the local
176 timezone changes, to be compatible with the old (default) behavior.
181 are specified, the option specified last wins.
182 .It Fl x Ar debugflag Ns Op , Ns Ar ...
183 Enable writing of debugging information to standard output.
184 One or more of the following comma separated
186 identifiers must be specified:
188 .Bl -tag -width ".Cm proc" -compact
192 make the other debug flags more verbose
194 be verbose when loading crontab files
196 be verbose about miscellaneous one-off events
198 be verbose about parsing individual crontab lines
200 be verbose about the state of the process, including all of its offspring
202 be verbose when iterating through the scheduling algorithms
204 trace through the execution, but do not perform any actions
208 .Bl -tag -width /etc/pam.d/cron -compact
211 .It Pa /etc/pam.d/cron
213 configuration file for
215 .It Pa /var/cron/tabs
216 Directory for personal crontab files
224 .An Paul Vixie Aq paul@vix.com