1 .\"/* Copyright 1988,1990,1993,1994 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
20 .Dd September 24, 2019
25 .Nd tables for driving cron
29 file contains instructions to the
31 daemon of the general form: ``run this command at this time on this date''.
32 Each user has their own crontab, and commands in any given crontab will be
33 executed as the user who owns the crontab.
34 Uucp and News will usually have
35 their own crontabs, eliminating the need for explicitly running
37 as part of a cron command.
39 Blank lines and leading spaces and tabs are ignored.
41 non-space character is a pound-sign (#) are comments, and are ignored.
42 Note that comments are not allowed on the same line as cron commands, since
43 they will be taken to be part of the command.
44 Similarly, comments are not
45 allowed on the same line as environment variable settings.
47 An active line in a crontab will be either an environment setting or a cron
49 An environment setting is of the form,
54 where the spaces around the equal-sign (=) are optional, and any subsequent
57 will be part of the value assigned to
61 string may be placed in quotes (single or double, but matching) to preserve
62 leading or trailing blanks.
65 string may also be placed in quote (single or double, but matching)
66 to preserve leading, trailing or inner blanks.
68 Several environment variables are set up
77 .Pa /sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin ,
84 line of the crontab's owner.
89 may be overridden by settings in the crontab;
95 variable is sometimes called
113 if it has any reason to send mail as a result of running
114 commands in ``this'' crontab.
117 is defined (and non-empty), mail is
118 sent to the user so named.
121 is defined (and non-empty), its value will be used as the from address.
123 may also be used to direct mail to multiple recipients
124 by separating recipient users with a comma.
127 is defined but empty (MAILTO=""), no
129 Otherwise mail is sent to the owner of the crontab.
131 option is useful if you decide on
134 .Pa /usr/lib/sendmail
136 your mailer when you install cron --
138 does not do aliasing, and UUCP
139 usually does not read its mail.
141 The format of a cron command is very much the V7 standard, with a number of
142 upward-compatible extensions.
143 Each line has five time and date fields,
144 followed by a user name
145 (with optional ``:<group>'' and ``/<login-class>'' suffixes)
146 if this is the system crontab file,
147 followed by a command.
148 Commands are executed by
150 when the minute, hour, and month of year fields match the current time,
152 when at least one of the two day fields (day of month, or day of week)
153 matches the current time (see ``Note'' below).
155 examines cron entries once every minute.
156 The time and date fields are:
157 .Bd -literal -offset indent
163 month 1-12 (or names, see below)
164 day of week 0-7 (0 or 7 is Sun, or use names)
167 A field may be an asterisk (*), which always stands for ``first\-last''.
169 Ranges of numbers are allowed.
170 Ranges are two numbers separated
172 The specified range is inclusive.
174 8-11 for an ``hours'' entry specifies execution at hours 8, 9, 10
178 A list is a set of numbers (or ranges)
180 Examples: ``1,2,5,9'', ``0-4,8-12''.
182 Step values can be used in conjunction with ranges.
184 a range with ``/<number>'' specifies skips of the number's value
186 For example, ``0-23/2'' can be used in the hours
187 field to specify command execution every other hour (the alternative
188 in the V7 standard is ``0,2,4,6,8,10,12,14,16,18,20,22'').
190 also permitted after an asterisk, so if you want to say ``every two
191 hours'', just use ``*/2''.
193 Names can also be used for the ``month'' and ``day of week''
195 Use the first three letters of the particular
196 day or month (case does not matter).
198 lists of names are not allowed.
200 The ``sixth'' field (the rest of the line) specifies the command to be
202 One or more command options may precede the command to modify processing
204 The entire command portion of the line, up to a newline or %
205 character, will be executed by
210 variable of the cronfile.
211 Percent-signs (%) in the command, unless escaped with backslash
212 (\\), will be changed into newline characters, and all data
213 after the first % will be sent to the command as standard
216 The following command options can be supplied:
219 No mail is sent after a successful run.
220 The execution output will only be mailed if the command exits with a non-zero
224 option is an attempt to cure potentially copious volumes of mail coming from
227 Execution will not be logged.
230 Duplicate options are not allowed.
232 Note: The day of a command's execution can be specified by two
233 fields \(em day of month, and day of week.
235 restricted (ie, are not *), the command will be run when
237 field matches the current time.
240 would cause a command to be run at 4:30 am on the 1st and 15th of each
241 month, plus every Friday.
243 Instead of the first five fields,
244 a line may start with
246 symbol followed either by one of eight special strings or by a numeric value.
247 The recognized special strings are:
248 .Bd -literal -offset indent
251 @reboot Run once, at startup of cron.
252 @yearly Run once a year, "0 0 1 1 *".
253 @annually (same as @yearly)
254 @monthly Run once a month, "0 0 1 * *".
255 @weekly Run once a week, "0 0 * * 0".
256 @daily Run once a day, "0 0 * * *".
257 @midnight (same as @daily)
258 @hourly Run once an hour, "0 * * * *".
259 @every_minute Run once a minute, "*/1 * * * *".
260 @every_second Run once a second.
265 symbol followed by a numeric value has a special notion of running
266 a job that many seconds after completion of the previous invocation of
268 Unlike regular syntax, it guarantees not to overlap two or more
269 invocations of the same job during normal cron execution.
270 Note, however, that overlap may occur if the job is running when the file
271 containing the job is modified and subsequently reloaded.
272 The first run is scheduled for the specified number of seconds after cron
273 is started or the crontab entry is reloaded.
274 .Sh EXAMPLE CRON FILE
277 # use /bin/sh to run commands, overriding the default set by cron
279 # mail any output to `paul', no matter whose crontab this is
282 # run five minutes after midnight, every day
283 5 0 * * * $HOME/bin/daily.job >> $HOME/tmp/out 2>&1
284 # run at 2:15pm on the first of every month -- output mailed to paul
285 15 14 1 * * $HOME/bin/monthly
286 # run at 10 pm on weekdays, annoy Joe
287 0 22 * * 1-5 mail -s "It's 10pm" joe%Joe,%%Where are your kids?%
288 23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"
289 5 4 * * sun echo "run at 5 after 4 every sunday"
290 # run at 5 minutes intervals, no matter how long it takes
291 @300 svnlite up /usr/src
292 # run every minute, suppress logging
294 # run every minute, only send mail if ping fails
295 * * * * * -n ping -c 1 freebsd.org
301 When specifying day of week, both day 0 and day 7 will be considered Sunday.
305 seem to disagree about this.
307 Lists and ranges are allowed to co-exist in the same field.
313 cron -- they want to see "1-3" or "7,8,9" ONLY.
315 Ranges can include "steps", so "1-9/2" is the same as "1,3,5,7,9".
317 Names of months or days of the week can be specified by name.
319 Environment variables can be set in the crontab.
325 environment handed to child processes is basically the one from
328 Command output is mailed to the crontab owner
330 cannot do this), can be
331 mailed to a person other than the crontab owner (SysV cannot do this), or the
332 feature can be turned off and no mail will be sent at all (SysV cannot do this
337 directives that can appear in place of the first five fields
340 Command processing can be modified using command options.
343 option suppresses logging.
346 option does not mail on successful run.
348 .An Paul Vixie Aq Mt paul@vix.com
350 If you are in one of the 70-odd countries that observe Daylight
351 Savings Time, jobs scheduled during the rollback or advance may be
354 is not started with the
357 In general, it is not a good idea to schedule jobs during
360 is not started with the
362 flag, which is enabled by default.
367 For US timezones (except parts of AZ and HI) the time shift occurs at
369 For others, the output of the
373 option can be used to determine the moment of time shift.
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