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Top Forums UNIX for Dummies Questions & Answers differnce between working of at and crontab commands Post 70768 by Just Ice on Tuesday 3rd of May 2005 11:43:52 PM
Old 05-04-2005
at is usually for non-regular, one-time-only jobs while cron is usually for regular, perpetual jobs ...

at samples:
Code:
# harass the console user at 7:05 pm
at 1905
echo "This is my console!" > /dev/console
# reboot the box 1 hour from now
at now + 1 hour
sync; sync; reboot

cron samples:
Code:
# reboot host every weekday @ 8:30 pm
30 20 * * 0-5 (sync; sync; init 6) > /dev/null 2>&1
# annoy the console user every weekday @ 8:00 am
00 08 * * 0-5 echo "This is my concole!" > /dev/console

however, you can also get a job to go regularly with an at command by adding something like this in your script ...
Code:
at now + 1 week << GO
/path/to/this/script > /dev/null 2>&1
GO

... and a "one-time" job in cron ... (will only run when all time conditions are met) ...
Code:
# run the job at 1:01 am Monday, January 1
01 01 01 01 1 echo "This is my console!" > /dev/console

btw, it would be best if you get into checking the man pages while you're just starting ... see "man at" and "man crontab" ...
 

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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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