[lxc-devel] Howto user namespaces?

[Serge Hallyn]

Quoting richard -rw- weinberger (richard.weinberger at gmail.com):
> On Tue, Apr 9, 2013 at 5:28 AM, Serge Hallyn <serge.hallyn at ubuntu.com> wrote:
> > Quoting richard -rw- weinberger (richard.weinberger at gmail.com):
> >> Am I missing something obvious?
> >
> > lxc-create does not yet convert the rootfs to the mapped uids, so you
> > need to do that manually using uidmapshift.  Check the
> > container-userns-convert script at
> > https://code.launchpad.net/~serge-hallyn/+junk/nsexec or in the nsexec
> > package at ppa:serge-hallyn/userns-natty.
> 
> Hmm, I've fixed the uids already by hand.
> Today I've created a new container and used container-userns-convert
> but with the same results.
> 
> What I find very strange is that your script does:
> lxc.id_map = U ${uid} 0 $range
> lxc.id_map = G ${uid} 0 $range
> uid is 100000, range is 10000.
> 
> But the lxc docs say:
>               Four values must be provided.  First a character, either
>               'u', or 'g', to specify whether user or group ids are
>               being mapped.  Next is the first userid as seen in the
>               user namespace of the container.  Next is the userid as
>               seen on the host.  Finally, a range indicating the number
>               of consecutive ids to map.
> 
> So, this would make more sense: lxc.id_map = u 0 100000 10000

Dwight recently made some changes to the lxc support.  I may not have
switched my scripts yet.

> Anyways, mount of tmpfs fails with ENOPERM, is there any debugging
> mechanism to find out why it is failing?

Yeah, get your kernel source and check to see in mm/shmem.c whether
tmpfs's fs_flags is given FS_USERNS_MOUNT

> According to strace some bind mounts before the tmpfs work perfectly fine.
> 
> --
> Thanks,
> //richard