linux-kernel - Inotify and UNIX domain sockets

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Message-ID: <CAKW9VBj-tyfgCTAip7jvwRP4v_LZe9jUtZRLewft81Rbb6y0yw@mail.gmail.com>
Date:	Wed, 18 Apr 2012 10:45:17 +0200
From:	alexandre p <ataaroap@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Inotify and UNIX domain sockets

Hello list,

I have a simple daemon program that creates an AF_UNIX socket which it
uses for local communication, absolutely nothing fancy. A somewhat
minor annoyance with UNIX sockets is that the socket file may be
removed at the filesystem level, and the listening process isn't aware
of it. To that end I decided to use inotify to watch the socket and
kill the daemon if it gets removed.

This doesn't appear to work. Specifically, no inotify event is
generated for a *connected* UNIX domain socket on my system. If the
socket is unconnected, then a delete event is properly generated, and
a regular file with the same name of course works fine. But for a
connected socket, nothing (perhaps because the file is not in fact
unlinked in this instance, a reference to the inode being maintained
by the socket subsystem itself? This is a wild guess.)

The question is, is this by design?

Here at work I'm using a somewhat ancient version of the kernel, so my
apologies in advance if this was a known bug at some point that has
since been fixed. Unfortunately I cannot test it on a more recent
version easily.

Linux devx 2.6.18-128.el5 #1 SMP Wed Dec 17 11:41:38 EST 2008 x86_64
x86_64 x86_64 GNU/Linux

Best regards,

Alexander
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