Hello,

Case: If I want to run a script background and logout, which command should I use ?

1)# ./script_name &
2)# nohup script_name
3)# nohup script_name &

And any differences ?

What happens if I redirect the output to a file?

I learned somewhere that the (1) format will stop after you logout, because the kernel sends SIGHUP to all of your processes after the Shell exits. But my experence told me that the script keep running after I logout.

So, I am confused here:

Could someone giudes me out...
Thanks,

I may be very wrong here, but I think the best route would be to use #3.

The first may work if the process you're running does not exit on SIGHUP. Some, such as inetd, simply reread their config and keep processing. Some of the scripts I write ignore SIGHUP purposely.

The second will trap SIGHUP, but not place it in the background right away. I believe it will is you press "susp", Control-Z in my case.

The last will trap SIGHUP, and run the job in the background.

Again, these may not be correct, since I'm working from memory here.

If you don't redirect the output to a file it will go to a file called nohup.out.

Otherwise, output goes where you specify.

Do a "man nohup" for more info.

3)# nohup script_name &

thats the right one....

nohup = the process is the child of the id 1
script_name = starts the script
& = starts the script in backround, otherwise you could not exit your terminal....

greetings pressy

Thanks for reply.

Yes, I knew the "script_name &" can put it background and I can logout, then check it next time login. Suppose the script doesn't trap any signal, or exit on signal, just an infinite loop and sleep, my confusion is if "script_name & " can have the job done, why prefer to use 'nohup'? What's benificial of using 'nohup'?

"man nohup" says it immune to SIGHUP. From user's point of view, if I don't trap or exit on SIGHUP, is there any reason that I must or better use "nohup" to start the script?

The default action for HUP is to exit. If you don't defeat that somehow, your script will exit when it gets a HUP. nohup is one way. And scripts can ignore HUP if they want to. If a script is explicitly ignoring HUP, nohup is not also needed. But some people will use nohup rather than checking the script.