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Full Discussion: Cron jobs
Operating Systems Linux Cron jobs Post 302383214 by gjkrpan on Monday 28th of December 2009 09:59:39 PM
Old 12-28-2009
Unless there's real urgent need to change it, you should leave /etc/crontab as is. The primary use of /etc/crontab is to allow the system to manage its own log files and environments. If there are tasks that you would like to include in the system housekeeping to be maintained at the times listed within /etc/crontab, they can be included in the appropriate /etc/cron.<time> file.

For purposes of a database backup, 'crontab -e' is the best option. Create your crontab entry and reference a script. This way you will not need to modify your crontab entry unless you need to change the time of your backup. All other aspects of the backup will be controlled from the script.

Deleting the old backup files will depend on how you perform your backups. If you perform a full database backup every night, then you can use something along the lines of this at the top of your script to remove the oldest file prior to performing the nightly backup:

find /backup-dir -atime +7 -exec rm ()\;

This will remove any files older than 7 days from the directory. Since this executes every night, there will only ever be one file deleted per night.

If you're performing a full backup the first night, and incrementals on subsequent nights, then you'd want to only perform the removal operation prior to your full backup with something similar to the following prior to performing the backup (assuming you perform your full backup on Monday):

Code:
if [ "`date +%a`" == "Mon" ]
then
    cd /backup-dir
    /bin/rm backup-files
fi

That will preserve your incremental backups until the night of your next full backup.

Hope this helps.

Last edited by Scott; 12-28-2009 at 11:06 PM.. Reason: Added code tags
 

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CRONTAB(1)						    BSD General Commands Manual 						CRONTAB(1)

NAME
crontab -- maintain crontab files for individual users (V3) SYNOPSIS
crontab [-u user] file crontab [-u user] { -l | -r | -e } DESCRIPTION
The crontab utility is the program used to install, deinstall or list the tables used to drive the cron(8) daemon in Vixie Cron. Each user can have their own crontab, and they are not intended to be edited directly. (Darwin note: Although cron(8) and crontab(5) are officially supported under Darwin, their functionality has been absorbed into launchd(8), which provides a more flexible way of automatically executing commands. See launchctl(1) for more information.) If the /usr/lib/cron/cron.allow file exists, then you must be listed therein in order to be allowed to use this command. If the /usr/lib/cron/cron.allow file does not exist but the /usr/lib/cron/cron.deny file does exist, then you must not be listed in the /usr/lib/cron/cron.deny file in order to use this command. If neither of these files exists, then depending on site-dependent configuration parameters, only the super user will be allowed to use this command, or all users will be able to use this command. The format of these files is one username per line, with no leading or trailing whitespace. Lines of other formats will be ignored, and so can be used for com- ments. 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 following options are available: -u Specify 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(1) can confuse crontab and that if you are running inside of su(1) you should always use the -u option for safety's sake. -l Display the current crontab on standard output. -r Remove the current crontab. -e Edit the current crontab using the editor specified by the VISUAL or EDITOR environment variables. The specified editor must edit the file in place; any editor that unlinks the file and recreates it cannot be used. After you exit from the editor, the modified crontab will be installed automatically. FILES
/usr/lib/cron/cron.allow /usr/lib/cron/cron.deny DIAGNOSTICS
A fairly informative usage message appears if you run it with a bad command line. SEE ALSO
crontab(5), compat(5), cron(8), launchctl(1) STANDARDS
The crontab command conforms to IEEE Std 1003.2 (``POSIX.2''). The new command syntax differs from previous versions of Vixie Cron, as well as from the classic SVR3 syntax. AUTHORS
Paul Vixie <paul@vix.com> BSD
December 29, 1993 BSD
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