обьясните синтаксис crontab

Usmanova72

Asgard

 

     The format of a cron command is very much the V7 standard, with a number

     of upward-compatible extensions.  Each line has five time and date

     fields, followed by a user name (with optional ``:<group>'' and

     ``/<login-class>'' suffixes) if this is the system crontab file, followed

     by a command.  Commands are executed by cron(8) when the minute, hour,

     and month of year fields match the current time, and when at least one of

     the two day fields (day of month, or day of week) matches the current

     time (see ``Note'' below).  cron(8) examines cron entries once every

     minute.  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 inclusive.  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.  Following 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 execution 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 particular day or month (case doesn't mat-

     ter).  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 % char-

     acter, 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 example, ``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.

     Instead of the first five fields, one of eight special strings may

     appear:

           string          meaning

           ------          -------

           @reboot         Run once, at startup.

           @yearly         Run once a year, "0 0 1 1 *".

           @annually       (same as @yearly)

           @monthly        Run once a month, "0 0 1 * *".

           @weekly         Run once a week, "0 0 * * 0".

           @daily          Run once a day, "0 0 * * *".

           @midnight       (same as @daily)

           @hourly         Run once an hour, "0 * * * *".

EXAMPLE CRON FILE

     # use /bin/sh to run commands, overriding the default set by cron

     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"

 

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Usmanova72

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