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From: stroyan@hpfcso.HP.COM (Mike Stroyan)
Newsgroups: comp.sys.hp
Subject: Re: stdout problems on HP/UX 6.5
Message-ID: <7370148@hpfcso.HP.COM>
Date: 1 Jun 90 17:28:32 GMT
References: <22441@dartvax.Dartmouth.EDU>
Organization: Hewlett-Packard, Fort Collins, CO, USA
Lines: 20

> All our applications run under X windows (currently 
> running all R4 binaries and using the corresponding
> libraries.  Our applications fork off a window and then
> exit.  For example,
  
> Ok, now here comes the problem.  When the child tries
> to print to stdout, the application window disappears.

Your child process is receiving a SIGKILL resulting from a SIGTTOU
signal to a process with parent process id 1.  You have "stty tostop"
set on your tty, indicating that background processes should be stopped
when they write to the tty.  As described in signal(5), the stop action
is changed to a SIGKILL for children of init.  I suppose the designers
felt that an orphan didn't have much hope of being woken up again.

You can prevent this behaviour by setting "stty -tostop" or by the
equivalent ioctl call on stdout.  Or you can ignore the suspend signal
by calling "signal(SIGTTOU, SIG_IGN);" after forking the child.

Mike Stroyan, stroyan@hpfcla.hp.com