SIGTTIN when running with &

Massyn has asked for the wisdom of the Perl Monks concerning the following question:

#!/fellow/monks.pl

I've coded a perl script to report the status of our Tivoli environment. Everything works fine when I run the script, however, when I put the script in the background with the & operator, the script terminates with the following error.

1 + Stopped (SIGTTIN) nohup ./sm-status.sh &

I could isolate the problem down to this line of code, which executes an rsh to a remote AIX server. rsh works fine, as said before, I can execute the script without a problem.

$tmp = `rsh aixhost2 df -k | awk {'print \$4,\$7'} | grep -v \"Mounted
+\"`;
[download]

Thanks!

#!/massyn.pl

You never know how important a backup is until you need it.

Comment on SIGTTIN when running with & Download Code

Replies are listed 'Best First'.
Re: SIGTTIN when running with & by amphiplex (Monk) on Nov 11, 2002 at 10:06 UTC
Hi ! Maybe you should run rsh with the `-n` option ? This option redirects input from /dev/null, it fixed the problem for me. ---- amphiplex	[reply]
Re: SIGTTIN when running with & by joe++ (Friar) on Nov 11, 2002 at 10:12 UTC
Hmm... something with connectivity to a terminal? man signal(7) says: `Signal Value Action Comment -------------------------------------- SIGTTIN 21,21,26 D tty input for background process ... D Default action is to stop the process.` [download] (Note: manual page from Debian Linux on i386 arch.). -- Cheers, Joe	[reply] [d/l]
Re: SIGTTIN when running with & by MZSanford (Curate) on Nov 11, 2002 at 13:56 UTC
Any time you run an external program, you run this risk. If the program you are running tries to open the `tty` to which it is connected, this will happen. I have seen this a great many times with batch perl processes. I guess you have a few options. With `rsh`, i believe someone mentioned the `-n` option, which fixes this. With some other programs (and even some XS modules) where a similar option is not avaialble, i have found i normally have to open a second terminal, start the program with a `nohup`, and close that terminal... or run programs using `cron` or `at`. from the frivolous to the serious	[reply] [d/l] [select]