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Top Forums Shell Programming and Scripting crontab entry modification using shell script Post 302124349 by Perderabo on Friday 29th of June 2007 11:30:36 PM
Old 06-30-2007
My suggestion is do not do that! First of all, simply changing the crontab file is NOT correct. You must use the crontab command or cron will not notice the change.

But what you should do is make the entry in root's crontab a shell script. And the shell script should, at the top, do something like:
Code:
if [ -f /var/root-crontab-control/inhibit-file1 ] ; then
        exit 0
fi

This is much cleaner than having scripts that fiddle with root crontab. Sooner or later the scripts fail and root is left with no crontab. With the inhibit-file concept, you just touch a file to inhibit the corresponding cronjob and then later you remove the inhibit file when you the script to run all the way.
 

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CRONTAB(1)						      General Commands Manual							CRONTAB(1)

NAME
crontab - maintain crontab files for individual users (ISC Cron V4.1) SYNOPSIS
crontab [-u user] file crontab [-u user] [-l | -r | -e] DESCRIPTION
Crontab is the program used to install, deinstall or list the tables used to drive the cron(8) daemon in ISC Cron. Each user can have their own crontab, and though these are files in /var, they are not intended to be edited directly. If the cron.allow file exists, then you must be listed therein in order to be allowed to use this command. If the cron.allow file does not exist but the cron.deny file does exist, then you must not be listed in the cron.deny file in order to use this command. If neither of these files exists, only the super user will be allowed to use this command. If the -u option is given, it specifies the name of the user whose crontab is to be tweaked. If this option is not given, crontab examines "your" crontab, i.e., the crontab of the person executing the command. Note that su(8) can confuse crontab and that if you are running inside of su(8) you should always use the -u option for safety's sake. The first form of this command is used to install a new crontab from some named file or standard input if the pseudo-filename ``-'' is given. The -l option causes the current crontab to be displayed on standard output. The -r option causes the current crontab to be removed. The -e option is used to edit the current crontab using the editor specified by the VISUAL or EDITOR environment variables. After you exit from the editor, the modified crontab will be installed automatically. SEE ALSO
crontab(5), cron(8) FILES
/etc/cron.allow /etc/cron.deny STANDARDS
The crontab command conforms to IEEE Std1003.2-1992 (``POSIX''). This new command syntax differs from previous versions of Vixie Cron, as well as from the classic SVR3 syntax. DIAGNOSTICS
A fairly informative usage message appears if you run it with a bad command line. AUTHOR
Paul Vixie <vixie@isc.org> 4th Berkeley Distribution 29 December 1993 CRONTAB(1)
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