[lxc-users] Mounting additional volume on container

[Christian Benke]

Hello!

Planning to move from OpenVZ to LXC, I started playing with containers
on my workstation yesterday. In the past hours I've been trying to
mount an additional volume to a container, but don't seem to get this
apparently trivial task right and I have difficulties identifying the
cause of the issue.

This is my mostly vanilla container-config (Using LVM as backingstore):

lxc.include = /usr/share/lxc/config/ubuntu.common.conf
lxc.include = /usr/share/lxc/config/ubuntu.userns.conf
lxc.arch = x86_64
lxc.id_map = u 0 100000 65536
lxc.id_map = g 0 100000 65536
lxc.rootfs = /dev/lxc/lxc_test_ubuntu
lxc.utsname = lxc_test_ubuntu
lxc.network.type = veth
lxc.network.flags = up
lxc.network.link = lxcbr0
lxc.network.hwaddr = 00:16:3e:b5:11:fb
lxc.cgroup.devices.allow = b 252:2 rwm
lxc.mount.entry = /media/benke/755f788b-3930-44e9-b7b8-cb93a3ec5af0
bla none bind 0 0


When the mount-point "/bla" has not been created in the container, the error is:

"lxc-start 1443952415.367 ERROR    lxc_utils - utils.c:safe_mount:1419
- No such file or directory - Mount of
'/media/benke/755f788b-3930-44e9-b7b8-cb93a3ec5af0' onto
'/usr/lib/x86_64-linux-gnu/lxc/bla' failed"

and when I create the mount-point "/bla" in the container, I get the error:

"lxc-start 1443952688.974 ERROR    lxc_utils - utils.c:safe_mount:1419
- Permission denied - Mount of
'/media/benke/755f788b-3930-44e9-b7b8-cb93a3ec5af0' onto
'/usr/lib/x86_64-linux-gnu/lxc/bla' failed."


Using "lxc.mount.entry = /dev/lxc/mount_test bla ext4 defaults 0 0"
instead of bind gives error "Operation not permitted" as well.
I've also tried to use "dir=create" as a mount-option, mounting a
block-device instead of using bind or a lv (WIth the correct
cgroup-settings of course), tested it on a container with the regular
filesystem as backingstore instead of lvm, tried "lxc.aa_profile =
unconfined", used  and manually created
"/usr/lib/x86_64-linux-gnu/lxc/bla" chmodded with the unprivileged
users rights out of desperation, even tried it with a privileged
container, but none of that made a difference. The error-messages
where always the same.

Reading all the threads and blogposts about this issue make it out to
be straightforward after ironing out typos or
cgroup-settings[1][2][3][4], but I'm not getting anywhere with the
changes.

What confuses me is the intransparency of how the mount is supposed to
work according to the lxc-logfile. Why is it trying to mount to
"/usr/lib/x86_64-linux-gnu/lxc/bla", not mounting to
/var/lib/lxc/lxc_test_ubuntu/rootfs/ or the real lvm-root?

I'm using Ubuntu 14.04 and stock LXC 1.0.7 from the package-manager.

Thanks in advance for all helpful advice!

Kind regards,
Christian


[1] https://lists.linuxcontainers.org/pipermail/lxc-users/2014-February/006257.html
[2] https://lists.linuxcontainers.org/pipermail/lxc-users/2014-February/006174.html
[3] https://www.mail-archive.com/lxc-users@lists.sourceforge.net/msg01208.html
[4] https://github.com/lxc/lxc/issues/78