differnce between working of at and crontab commands

doddas · #1 (**permalink**) 05-03-2005

h I would like to know the differnce (both working and how) between at command and crontab..

Thanks in advance
Satish D

Just Ice · #2 (**permalink**) 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" ...

solaris-ninja · #3 (**permalink**) 05-04-2005

Quote:

Originally Posted by Just Ice

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" ...

Very interesting answer. Good Job.

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