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List:       log
Subject:    Re: daemon tools under Solaris
From:       prj () po ! cwru ! edu (Paul Jarc)
Date:       2001-10-16 17:42:35
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Jason Kawaja <kawaja@ece.ufl.edu> wrote:
> On Tue, 16 Oct 2001, Dan Rench wrote:
>> SV:123456:respawn:/command/svscanboot < /dev/null
>
> it's my understanding that svscanboot simply runs svscan with some extras
> (i have daemontools 0.70). so why is a continuous eof needed for svscan?

The reason for redirecting descriptor 0 from /dev/null is that your
daemons should not be reading from the console, and on some systems (I
think), init runs the commands in inittab with descriptor 0 reading
from /dev/console.

svscanboot already does "exec < /dev/null".  The reason for doing this
again in the inittab line is that on some systems including Solaris,
init starts its commands with no open file descriptors, so when
/bin/sh opens the script, the script is on descriptor 0, and on some
systems including Solaris, /bin/sh does not protect itself from losing
the script descriptor via a redirection in the script.

> it's also my understanding that sending a continuous eof to a process that
> is still attached to a terminal device effectively blocks anything from
> being read from that device for that process..

The process will see only EOF on that descriptor, but it can still
open /dev/tty to get a descriptor for the terminal and read from that.

> however a check on my svscan process shows no terminal device
> assignment.

As it should be.  But a process can have a descriptor for a terminal,
while also not having a controlling terminal.  svscanboot might have
been started with descriptor 0 reding from /dev/console, even though
it had no controlling tty.

> i run svscan from inittab (solaris) without any assignment and services
> work properly.

If you're not using svscanboot, then you're avoiding the /bin/sh bug
that svscanboot triggers, and which the redirection in inittab
circumvents.


paul

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