I have a simple .sh file ,I want linux to call this at boot up , please advice me how to .

Call it from one of the system startup scripts.

I can't be more specific without knowing which distribution you're using, but calling it from rc.local (usually found in /etc, /etc/init.d or /etc/rc.d) is pretty much guaranteed to work.

here is my cat /proc/version

I've never seen a Redhat-based release that didn't run /etc/rc.local on boot. That's not to say they don't exist, most of my experience is with Fedora, but there's no harm in trying.

For Ubuntu, or any variant of; Add the script to /etc/init.d/ give it the proper persmission and update rc.d with defaults for that script.

Lets say your script name is script.sh; copy the script to the /etc/init.d/ dir from the command line then chmod it. Then run, "update-rc.d script.sh defaults". It will then run on next boot.

one option is adding it to your .bash_profile. another option would be adding an @reboot line to your crontab.

Adding it to the .bash_profile will only run it when a user logs in, whereas the OP wants it run at every boot. I think that the crontab option would work, but I think simply adding it to rc.local would be simpler (personal preference, though).

You can add it to cron with @boot as the option.

IMO, adding the script to rc.local/rc.d is much simpler than tinkering with crontab. In some cases the daemon is not enabled by default. With crontab, the trival task of making a script run on boot, then becomes a hassle for beginners. I prefer updating rc.d to crontab.

Sure, crontab is great for running scripts every n minutes but you could achieve the same with the watch command. Watch allows you to specify the job frequency in seconds. Unlike cron, which only allows minutes.

I say stick with adding the script to rc.local/rc.d! Daemonize with the screen command and the -dmS switches.

Which shell are the d, m and S options for?

@Catkin, the dmS switches are used with Bash. I'm sorry, i did not specify that the -dms switches are used with the screen command and not the watch command.

Example:
above code runs as a daemon every 60 seconds from boot. screen detaches the proc, and watch runs the proc every n seconds.

chmod
drop script into /etc/init.d/ directory
run-> update-rc.d scriptname.sh defaults
reboot

unnecessary post.

That does not work on all distros (and the chmod is missing some arguments).

If the .sh file is run from the boot scripts such as rc.local, the boot process will not continue until the .sh file finishes running. If this matters, the .sh file can be run in the background and the boot scripts allowed to continue by putting & after the file's name to "background" it.

I know the chmod is missing arguments lol Specifically chmod u+x scriptname.sh and I didn't say it works on all distros either. I have only tested it on Ubuntu versions 10.10 - 12.04.

OK.

We don't know which distro fachhoch@gmail.com is using or their familiarity with the chmod command. Advice that may not work is confusing for beginners.