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

[Dwight Engen]

On Thu, 13 Feb 2014 13:32:44 -0500
"Michael H. Warfield" <mhw at WittsEnd.com> wrote:

> 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.

Hey Mike, hmm, I'm just wondering where it is getting created in the
native host case? I think if we can get the container to do it itself
that would be better than adding stuff to lxc, but maybe that isn't
feasible.

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