| CRONTAB(5) | File Formats Manual | CRONTAB(5) | 
crontab —
crontab file contains instructions to the
  cron(8) daemon of the general
  form: “at these times on these dates run this command”. There
  may be a system crontab and each user may have their
  own crontab. Commands in any given
  crontab will be executed either as the user who owns
  the crontab or, in the case of the system
  crontab, as the user specified on the command line.
While a crontab is a text file, it is not
    intended to be directly edited. Creation, modification, and removal of a
    crontab should be done using
    crontab(1).
Blank lines, leading spaces, and tabs are ignored. Lines whose
    first non-space character is a pound sign
    (‘#’) are comments, and are ignored.
    Note that comments are not allowed on the same line as
    cron(8) commands, since they
    will be taken to be part of the command. Similarly, comments are not allowed
    on the same line as environment variable settings.
An active line in a crontab is either an
    environment variable setting or a
    cron(8) command.
Environment variable settings create the environment any command
    in the crontab is run in. An environment variable
    setting is of the form:
name = valueThe spaces around the equal sign
    (‘=’) are optional, and any subsequent
    non-leading spaces in value will be part of the value
    assigned to name. The value
    string may be placed in quotes (single or double, but matching) to preserve
    leading or trailing blanks.
Lines in the system crontab have six fixed
    fields plus a command, in the form:
While lines in a user crontab have five
    fixed fields plus a command, in the form:
Fields are separated by blanks or tabs. The command may be one or more fields long. The allowed values for the fields are:
| field | allowed values | 
| minute | * or 0–59 | 
| hour | * or 0–23 | 
| day-of-month | * or 1–31 | 
| month | * or 1–12 or a name (see below) | 
| day-of-week | * or 0–7 or a name (0 or 7 is Sunday) | 
| user | a valid username | 
| command | text | 
Lists are allowed. A list is a set of numbers (or ranges) separated by commas. For example, “1,2,5,9” or “0–4,8–12”.
Ranges of numbers are allowed. Ranges are two numbers separated with a hyphen. The specified range is inclusive. For example, 8–11 for an hour entry specifies execution at hours 8, 9, 10 and 11.
Step values can be used in conjunction with ranges. Following a range with /number specifies skips of number through the range. For example, “0–23/2” can be used in the hour field to specify command execution every other hour. Steps are also permitted after an asterisk, so to say “every two hours”, just use “*/2”.
An asterisk (‘*’) is short
    form for a range of all allowed values.
Names can be used in the month and day-of-week fields. Use the first three letters of the particular day or month (case doesn't matter). Ranges or lists of names are not allowed.
The command field (the rest of the line) is
    the command to be run. The entire command portion of the line, up to a
    newline or % character, will be executed by /bin/sh
    or by the shell specified in the SHELL variable of
    the crontab. Percent signs
    (‘%’) in the command, unless escaped
    with a backslash (‘\’), will be
    changed into newline characters, and all data after the first
    ‘%’ will be sent to the command as
    standard input.
Commands may be modified as follows:
-n
    command-n option is an attempt to cure potentially
      copious volumes of mail coming from
      cron(8).-q
    commandCommands are executed by cron(8) when the minute, hour, and month fields match the current time, and when at least one of the two day fields (day-of-month or day-of-week), match the current time.
Note: The day of a command's execution can be specified by two fields — day-of-month and day-of-week. If both fields are restricted (i.e. aren't *), the command will be run when either field matches the current time. For example,
30 4 1,15 * 5would cause a command to be run at 4:30 am on the 1st and 15th of each month, plus every Friday.
Instead of the first five fields, one of eight special strings may appear:
| string | meaning | 
| @reboot | Run once, at startup. | 
| @yearly | Run every January 1 (0 0 1 1 *). | 
| @annually | The same as @yearly. | 
| @monthly | Run the first day of every month (0 0 1 * *). | 
| @weekly | Run every Sunday (0 0 * * 0). | 
| @daily | Run every midnight (0 0 * * *). | 
| @midnight | The same as @daily. | 
| @hourly | Run every hour, on the hour (0 * * * *). | 
CRON_TZCRON_TZ variable can be set to an alternate
      time zone in order to affect when the job is run. Note that this only
      affects the scheduling of the job, not the time zone that the job
      perceives when it is run. If CRON_TZ is defined
      but empty (CRON_TZ=""), jobs are
      scheduled with respect to the local time zone.CRON_WITHINCRON_WITHIN variable should indicate the
      number of seconds within a job's scheduled time that it should still be
      run. On a heavily loaded system, or on a system that has just been
      “woken up”, jobs will sometimes start later than originally
      intended, and by skipping non-critical jobs because of delays, system load
      can be lightened. If CRON_WITHIN is defined but
      empty (CRON_WITHIN=""), or set to some
      non-positive value (0, a negative number, or a non-numeric string), it is
      treated as if it was unset.HOMEcrontab.LOGNAMEcrontab.MAILTOMAILTO is defined and non-empty, mail is sent
      to the user so named. If MAILTO is defined but
      empty (MAILTO = “”), no mail will be
      sent. Otherwise mail is sent to the owner of the
      crontab. This is useful for pseudo-users that lack
      an alias that would otherwise redirect the mail to a real person.SHELLcrontab.USERcrontab.# use /bin/sh to run commands, no matter what /etc/passwd says SHELL=/bin/sh # mail any output to `paul', no matter whose crontab this is MAILTO=paul # # run five minutes after midnight, every day 5 0 * * * $HOME/bin/daily.job >> $HOME/tmp/out 2>&1 # run at 2:15pm on the first of every month -- output mailed to paul 15 14 1 * * $HOME/bin/monthly # run at 10 pm on weekdays, annoy Joe 0 22 * * 1-5 mail -s "It's 10pm" joe%Joe,%%Where are your kids?% 23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday" 5 4 * * sun echo "run at 5 after 4 every sunday"
crontab file format is compliant with the
  IEEE Std 1003.1-2008 (“POSIX.1”)
  specification. The behaviours described below are all extensions to that
  standard:
-n.-q.@’ commands that can
      appear in place of the first five fields.crontab was written by Paul
  Vixie
  <vixie@isc.org>.
| June 14, 2018 | NetBSD 9.4 |