[lxc-devel] Centos template: symlink for /dev/fd missing? - And from Oracle too...

[Michael H. Warfield]

On Thu, 2014-02-13 at 12:18 -0500, Michael H. Warfield wrote:
> On Thu, 2014-02-13 at 14:02 +0100, Harald Dunkel wrote:
> > Hi folks,
> 
> > Problem in LXC (beta4) running a Centos 6.5 client:
> 
> > 	# cat <(echo hello)
> > 	cat: /dev/fd/63: No such file or directory
> 
> > On a "real" host /dev/fd is a symlink pointing to /proc/self/fd.
> > AFAICS only the altlinux template creates this symlink. Debian
> > seems to provide the link on its own.

> > lxc.autodev = 1 does not help. I tried, of course.
> 
> > Question: Should this symlink be added to the lxc-centos template,
> > as it was done for altlinux?

> Probably.  I'll have to look at it.  If the CentOS template needs it,
> then the Fedora template would also probably need it as well, especially
> in the autodev case.  The Oracle template also doesn't do anything
> with /dev/fd and it should be very similar to the CentOS layout.  I'm
> not sure what the deal is.  Maybe they're providing it in their startup.

Oh crud.  Isn't this a fine kettle of fish.

I've confirmed that /dev/fd is missing from CentOS and Oracle containers
but not from Fedora (systemd w/ autodev) containers.  Not exactly what I
was expecting.  I haven't tested it with earlier deprecated upstart or
sysvinit versions of Fedora.  I don't see where it's being created by
any of the init scripts.

I can add creating that symlink into the CentOS template, there's just
one problem.

As you noticed, it also doesn't work if you set autodev = 1.  Adding the
symlink into the CentOS and Oracle templates would fix the static fs
case but the autodev case (which should work with both, even with
sysvinit or upstart) will still be broken.  Maybe when CentOS 7, RHEL 7,
Oracle 7 comes out with systemd (which will require autodev), that will
fix itself.  With devtmpfs, that /dev/fd symlink has to be created
dynamically when the system inits and mounts devtmpfs on /dev.

In my mind, that symlink needs to be created at run-time if it doesn't
exist.  A workaround, right now, would be to add that to a hook (post
mount hook maybe?).  Longer term, I think that may need to be in the
lxc-start code itself, right where we're populating the /dev directory
with things like the pty's (is there any case where we would NOT want to
do this?).  We could also add a start-up script into the container
itself to do this as it inits but I would prefer keeping those kinds of
interventions to a minimum.

I'd like to hear Dwight's thoughts on this wrt the Oracle template
before we go down either road or another.

> > Every helpful comment would be highly appreciated
> > Harri
> 
> Regards,
> Mike

-- 
Michael H. Warfield (AI4NB) | (770) 978-7061 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!

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