suppose i want to run some command at some fixed time

how can i do it..............at 4:30 ls
is not working i dont know why throw some light

We might be able to shed some light if you were kind
enough to provide us with WHAT you are doing.

Usually you'll do something like

echo "halt" | at 23:00

or have the instructions that you want executed
listed in a file and invoke at with -f ... but all of this
you could have found out from the man-page.



Cheers,
Tink

Also, do you want to do this one time, or is it something you want to do every day or every week at a certain time?

At is used for one-time events; cron should be used for things that will be run on a regular basis, be it hourly, daily, weekly, or even once a year on a particular day.

At will also use the environment you have in effect at the time you submit the at schedule, using all your environment variables and paths. Cron will not have the same environment set, so you must supply full paths to scripts or utilities you use.

-Alan