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Full Discussion: Cron job randomly once a day
Top Forums Shell Programming and Scripting Cron job randomly once a day Post 302467901 by Neo on Monday 1st of November 2010 12:38:06 AM
Old 11-01-2010
You can simply generate a random number each day (with one crontab file that runs only once at the beginning of the day) that corresponds to the number of minutes (or 5 minute intervals) each day, and write that number to a file.

Then, you have a second crontab file that reads the random number in the file and checks against the time and executes if there is match.

If you are using PHP, you can also try to use PHP shared memory, or you could use an environmental variable to hold the daily random number. There are many ways to do this.

---------- Post updated at 04:38 ---------- Previous update was at 04:34 ----------

Quote:
Originally Posted by ctsgnb
maybe use the "at" command instead ?
While it is possible to set something up with the at command, the original poster asked for a crontab solution.

This is easily done with cron, as requested by the original poster.

(See my post above)
 

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crontab(5)							File Formats Manual							crontab(5)

Name
       crontab - clock daemon table file

Syntax
       /usr/lib/crontab

Description
       The  command  executes  at  specified dates and times according to the instructions in the file. The file consists of lines with six fields
       each.  The format for a line is as follows:

	      minute hour day month weekday command

       The following list defines each field in the line:

       minute (0-59)  The exact minute that the command sequence executes.

       hour (0-23)    The hour of the day that the command sequence executes.

       day (1-31)     The day of the month that the command sequence executes.

       month (1-12)   The month of the year that the command sequence executes.

       weekday (1-7)  The day of the week that the command sequence executes. Monday = 1, Tuesday = 2, and so forth.

       command	      The complete command sequence variable that is to be executed.  Note that the command string must conform  to  Bourne  shell
		      syntax.

       The first five integer fields may be specified as follows:

       o   A single number in the specified range

       o   Two numbers separated by a minus, meaning a range inclusive

       o   A list of numbers separated by commas, meaning any of the numbers

       o   An asterisk meaning all legal values

       The sixth field is a string that is executed by the shell at the specified times.  A percent sign (%) in this field is translated to a new-
       line character.	Only the first line of the command field, up to a percent sign (%) or end of line, is executed by the  shell.	The  other
       lines are made available to the command as standard input.

Examples
       The following example is part of a file:
       # periodic things
       0,15,30,45 * * * * (echo '^M' `date`; echo '') >/dev/console
       0,15,30,45 * * * * /usr/lib/atrun

       # daily stuff
       5 4 * * * sh /usr/adm/newsyslog
       15 4 * * * ( cd /usr/preserve; find . -mtime +7 -a -exec rm -f {} ; )
       20 4 * * * find /usr/msgs -mtime +21 -a ! -perm 444 -a ! -name bounds
	    -a -exec rm -f {} ;

       # NOTE: The above line is wrapped.

       # local cleanups
       30 4 * * * find /usr/spool/mqueue -type f -mtime +5 -name df-exec rm {} ;
       35 4 * * * find /usr/spool/mqueue -type f -mtime +5 -name tf-exec rm {} ;
       40 4 * * * find /usr/spool/rwho -type f -mtime +21 -exec rm {} ;
       #

       # redirecting error output
       0 17 * * 1,3,5 /bin/tar -cv /usr/sysads/smith > /dev/console 2>&1
       #

Files
See Also
       sh(1), cron(8)
       Guide to System Environment Setup

																	crontab(5)
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