initscripts bug
Bryn M. Reeves
breeves at redhat.com
Tue Dec 6 11:37:42 UTC 2005
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Sergey wrote:
> Just found a bug in netplugd after having traced it with strace. netplugd is a
> network plug-in/out monitoring daemon, performing the specified actions when
> such an event comes up. Comes with net-tools rpm.
>
> Alright, now the bug. Try to start/restart netplugd from a terminal:
> /sbin/service netplugd restart or /etc/init.d/netplugd restart. Starts up
> well. Good. Now start mc and run the above command again. It hangs up. Strace
> comes with:
>
> [pid 9404] write(1, "/etc/netplug.d/netplug eth0 prob"..., 46) = ?
> ERESTARTSYS (To be restarted)
> [pid 9404] --- SIGTTOU (Stopped (tty output)) @ 0 (0) ---
> [pid 9404] --- SIGTTOU (Stopped (tty output)) @ 0 (0) ---
>
> The cloned process is T (stopped).
>
> # ps axu | grep netplugd
> root 9699 0.0 0.1 1548 412 pts/2 S+ 14:23 0:00 netplugd
> root 9700 0.0 0.0 1552 252 pts/2 T 14:23 0:00 netplugd
>
> I am not sure why mc causes such a stop, anyway it is somehow related to
> terminal. What if such a script hangs up on a remote system reboot? Bad...
>
It stopped because it tried to write to the terminal while in the
background.
When a process running in the background tries to perform output on the
terminal, it is sent a SIGTTOU, causing it to stop.
I think you're seeing this as a side effect of how mc is running the
command. Of course, a demon shouldn't really be doing any terminal IO
anyway, so it may still indicate a bug in netplugd.
Kind regards,
Bryn.
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