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crontab



DESCRIPTION

       A crontab file contains instructions to the cron(8) daemon
       of the general form: ``run this command at  this  time  on
       this  date''.   Each  user has their own crontab, and com­
       mands in any given crontab will be executed  as  the  user
       who  owns  the  crontab.   Uucp and News will usually have
       their own crontabs, eliminating the  need  for  explicitly
       running su(1) as part of a cron command.

       Blank  lines  and  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 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 will be either an environment
       setting or a cron command.  An environment setting  is  of
       the form,

           name = value

       where  the  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.

       Several  environment variables are set up automatically by
       the cron(8) daemon.  SHELL is set to /bin/sh, and  LOGNAME
       and  HOME  are  set  from  the  /etc/passwd  line  of  the
       crontab's owner.  HOME and SHELL may be overridden by set­
       tings in the crontab; LOGNAME may not.

       (Another  note:  the  LOGNAME variable is sometimes called
       USER on BSD systems...  on these systems, USER will be set
       also.)

       In addition to LOGNAME, HOME, and SHELL, cron(8) will look
       at MAILTO if it has any reason to send mail as a result of
       running  commands  in  ``this''  crontab.   If  MAILTO  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  option  is  useful  if you decide on
       /bin/mail instead of /usr/lib/sendmail as your mailer when
       you  install  cron  --  /bin/mail doesn't do aliasing, and
       UUCP usually doesn't read its mail.

       The format of a cron command is very much the V7 standard,
       with  a number of upward-compatible extensions.  Each line

       The time and date fields are:

              field          allowed values
              -----          --------------
              minute         0-59
              hour           0-23
              day of month   1-31
              month          1-12 (or names, see below)
              day of week    0-7 (0 or 7 is Sun, or use names)

       A  field  may  be an asterisk (*), which always stands for
       ``first-last''.

       Ranges of numbers are allowed.   Ranges  are  two  numbers
       separated  with  a  hyphen.  The specified range is inclu­
       sive.  For example, 8-11 for an ``hours'' entry  specifies
       execution at hours 8, 9, 10 and 11.

       Lists are allowed.  A list is a set of numbers (or ranges)
       separated by commas.  Examples: ``1,2,5,9'', ``0-4,8-12''.

       Step  values can be used in conjunction with ranges.  Fol­
       lowing a range with ``/<number>'' specifies skips  of  the
       number's value through the range.  For example, ``0-23/2''
       can be used in the hours field to specify  command  execu­
       tion  every other hour (the alternative in the V7 standard
       is ``0,2,4,6,8,10,12,14,16,18,20,22'').   Steps  are  also
       permitted after an asterisk, so if you want to say ``every
       two hours'', just use ``*/2''.

       Names can also be used for  the  ``month''  and  ``day  of
       week'' fields.  Use the first three letters of the partic­
       ular day or month (case doesn't matter).  Ranges or  lists
       of names are not allowed.

       The  ``sixth''  field (the rest of the line) specifies 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  cronfile.   Percent-signs  (%) in the command, unless
       escaped with backslash (\), will be changed  into  newline
       characters, and all data after the first % will be sent to
       the command as standard input.

       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 (ie, aren't *), the command will  be
       run when either field matches the current time.  For exam­
       ple,
       ``30 4 1,15 * 5'' would cause a command to be run at  4:30
       am on the 1st and 15th of each month, plus every Friday.
       5 4 * * sun     echo "run at 5 after 4 every sunday"


SEE ALSO

       cron(8), crontab(1)


EXTENSIONS

       When  specifying day of week, both day 0 and day 7 will be
       considered Sunday.  BSD and ATT  seem  to  disagree  about
       this.

       Lists  and  ranges  are  allowed  to  co-exist in the same
       field.  "1-3,7-9" would be rejected by ATT or BSD cron  --
       they want to see "1-3" or "7,8,9" ONLY.

       Ranges  can  include  "steps",  so  "1-9/2" is the same as
       "1,3,5,7,9".

       Names of months or days of the week can  be  specified  by
       name.

       Environment  variables  can be set in the crontab.  In BSD
       or ATT, the environment handed to child processes is basi­
       cally the one from /etc/rc.

       If  the  uid  of the owner is 0, he can put a "-" as first
       character of a crontab entry. Then cron won't write a sys­
       log message about this command.

       Command  output  is mailed to the crontab owner (BSD can't
       do this), can be mailed to a person other than the crontab
       owner  (SysV  can't do this), or the feature can be turned
       off and no mail will be sent at all (SysV  can't  do  this
       either).


AUTHOR

       Paul Vixie <paul@vix.com>

                         24 January 1994               CRONTAB(5)
  

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