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Top Forums UNIX for Dummies Questions & Answers Execute crontab for every 4 hours and begin from current time Post 302526015 by Ganeshwari on Monday 30th of May 2011 04:47:03 AM
Old 05-30-2011
Execute crontab for every 4 hours and begin from current time

I want to add a crontab entry which should execute for every 4 hours and that 4 hours calculation should begin from the current time.

Normally if I set the crontab entry like this,

Code:
00 */4 30 05 * root date >>/tmp/cronout

The above will execute the date command for every 4 hours like 4,8,12,16,20,24 on 30th May, for example I start the crontab at 02:00:00. But if I start the crontab at 09:15:00, it should execute the crontab command after 4 hours like 13:15:00, then 17:15:00 like this.

Can any one please tell me, how to achieve this in crontab ?

Last edited by pludi; 05-30-2011 at 09:06 AM..
 

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bcrontab(1)						      General Commands Manual						       bcrontab(1)

NAME
bcrontab - Manage users crontab files SYNOPSIS
bcrontab [ -u user ] file bcrontab [ -u user ] { -l | -r | -e } DESCRIPTION
bcrontab interfaces with the bcron-spool daemon to manage crontab files in the privileged spool directory. OPTIONS
-u user Tell bcron-spool that we are acting on behalf of the named user. bcron-spool will only accept the username if bcrontab is running as either root or the same user ID as the named user. -l List the cronab crontab to standard output. -r Remove the user's crontab. -e Edit the current crontab. ENVIRONMENT
VISUAL If this is set, it is used as the editor to invoke to edit a crontab. EDITOR If $VISUAL is not set and this is, it is used as the editor to invoke to edit a crontab. If neither are set, /bin/vi is used. BCRON_SOCKET The path to the named socket used to communicate with bcron-spool. Defaults to /var/run/bcron-spool. LOGNAME USER These two variables are used, in order, to determine the user name invoking the program. One must be set if the -u option is not used. FILES
bcrontab tries to writes a temporary file into the current directory, and then into /tmp if that fails, in order to edit the current crontab. SEE ALSO
bcron-spool(8), crontab(5) AUTHOR
Bruce Guenter <bruceg@em.ca> bcrontab(1)
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