Shell Programming and Scripting

You don't have to use nohup, by-the-by. It only does things that your script can do by itself. So you could do it all on one script still perhaps:

Code:

#!/bin/ksh

some_foreground_stuff

echo "Input some data"
read SOMEVAR

(
        some_background stuff
        more background stuff
        etc
) >>nohup.out 2>&1 </dev/null & disown

echo "Background stuff is running"
exit 0

Very kewl, did not know about "disown". Regrettably the version of ksh on this server (Solaris 10) does not support disown. Why did you use "</dev/null", I know what it is but not why you used it.

Anyway while disown is not an option for the version of ksh being used , this did lead me to find the "-p" option for nohup. A test script similar to your example shows it appears to serve the same purpose:

Code:

#!/usr/bin/env ksh
 
interact with user

echo "script  will now run independently in background"
 
nohup -p $$
 
( 
  so something
  ...
)&
 
exit 0

If it doesn't support it, you don't even need it, so just remove it.

Because that's exactly what nohup does. Things that try to read from /dev/null will instantly get 'end of file', which is better than an error like 'invalid file descriptor' that you'd get from actually closing the file. See man nohup.

I don't know what -p does, my system doesn't have it. But the nohup is entirely redundant here. Your script also doesn't work like it should since you're not doing redirections on the part inside the subshell anymore. If you just did redirections the way I did in the first place instead of ripping them out...

Code:

#!/usr/bin/env ksh
 
interact with user

echo "script  will now run independently in background"
 
( 
  so something
  ...
) >>nohup.log 2>&1 </dev/null &
 
exit 0

If the nohup is redundant in my example would not the disown be redundent as well? or to put it another way what does the disown do that the redirection in conjunction with putting the script in the backgound not do?

As to the redirection of script output, the "real" script already redirects its output to a file defined at run time.

From the man nohup page:

/usr/bin/nohup -p [-Fa] pid [pid]...
-p Operates on a list of processes.
-F Force. Grabs the target processes even if another pro-
cess has control.
-a Always changes the signal disposition of target
processes.

Some shells won't actually quit after backgrounding something, they'll wait for background jobs. To tell it to give up and leave processes behind, you must disown them first.

Shells which don't have "disown", don't do that anyway, so you don't need it.

Some shells need it to leave a subshell or background process running around by itself. Some don't. Yours doesn't.