[linux-audio-user] jackd fails to start: cannot create shm segment /jack-shm-registry (No such file or directory)

Jack O'Quin joq at io.com
Fri Apr 18 14:45:01 EDT 2003


"Mark Knecht" <mknecht at controlnet.com> writes:

> Jack,
>    I found (in my Redhat case) that there is support for something that
> 'replaces' the shm file system in the kernel I built this morning, but when
> I went to mount it I found that /dev/shm doesn't exist. I know from my 1394
> work that these things have to be created correctly, but I do not know how
> to do it. Do you know of any documentation on the right way to get this
> created? I admit I have not searched the Jack archives yet.

Mount points are ordinary directories.  To create it (as root)...

  # mkdir /dev/shm

Most things in /dev are device special files, created with mknod (or
MAKEDEV).  But, this is just a mount point.  It's odd that the POSIX
shm implementors put it in that directory, but there it is.

>    What value does this provide, by the way? Jack seemed to be working just
> fine for me up to now.

Paul changed from System V shared memory to the POSIX shm interface.
System V had a bad habit of leaving garbage segments around after
applications terminate.  POSIX shm is cleaner, and is also available
on Apple OS X.

I don't think Paul initially realized that most Linux systems are not
configured out of the box for this to work.  Who would have thunk it?

This problem only arises with CVS versions of JACK.  At one point,
Paul said he was considering changing JACK to support both, with
automatic configuration at build time.  I don't know what the status
of that is, or even whether I think it's a good idea.

At this point, it seems like mostly a big documentation problem.

Regards,
-- 
  Jack O'Quin
  Austin, Texas, USA



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