GNU bug report logs - #15779
timeout: Child gets SIGTTOU when run from a shell script

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: "Richard W.M. Jones" <rjones <at> redhat.com>
To: Pádraig Brady <pbrady <at> redhat.com>
Cc: Report bugs to <bug-coreutils <at> gnu.org>
Subject: Re: timeout: Child gets SIGTTOU when run from a shell script
Date: Fri, 1 Nov 2013 12:17:37 +0000

[Message part 1 (text/plain, inline)]

On Fri, Nov 01, 2013 at 11:53:44AM +0000, Pádraig Brady wrote:
> Probably something to do with job control
> If you `set -m` first in the script,
> then the test binary doesn't hang.

Unfortunately set -m isn't quite right for the script
we are interested in fixing:

https://github.com/libguestfs/libguestfs/blob/master/run.in#L217

> I did a version of timeout once that put the child in it's own group,
> and noted in that version that I needed to leave SIGTTOU as IGN
> as tcsetpgrp(0, getpid()) caused SIGTTOU to be sent and I wasn't sure why.

That sounds like a very similar situation to this one.  The
tty_check_change function is called all over the place, so just about
any ioctl or flush or tc* function could cause SIGTTOU to be sent.

> Maybe we should be resetting SIGTT{OU,IN} to what it was
> previously set to, rather than SIG_DFL?

The attached patch does *not* work .. don't know if you can see
any obvious mistakes.

Yesterday I looked through the strace -f output between the two cases
and came to the conclusion that it's not about signal handlers at all.
(What it's about is a mystery ...)

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://people.redhat.com/~rjones/virt-df/

[timeout.patch2 (text/plain, attachment)]

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