LXC: How do I mount a folder from the host to the container?

Question

I'm trying to mount a folder on the host to an LXC container.

The host has a folder /mnt/ssd/solr_data created (this is currently on the root filesystem, but later I'll mount an SSD drive there, so I'm prepping for that).

I want that folder to mount as /data in the container.

So in the containers fstab file I have the following:

/mnt/ssd/solr_data      /var/lib/lxc/Solr4StandAlone/rootfs/data        ext4    defaults,noatime        0       0

But that's a no-go, I get this error starting the container:

lxc-start: No such file or directory - failed to mount '/mnt/ssd/solr_data' on '/usr/lib/x86_64-linux-gnu/lxc//data'
lxc-start: failed to setup the mounts for 'Solr4StandAlone'
lxc-start: failed to setup the container
lxc-start: invalid sequence number 1. expected 2
lxc-start: failed to spawn 'Solr4StandAlone'

Solution 1

To create the directory automatically in the container, you can also add the create=dir option in the fstab :

/mnt/ssd/solr_data      /var/lib/lxc/Solr4StandAlone/rootfs/data        none   bind,create=dir

Edit : this is specific to LXC. See this thread

Just like we already had "optional", this adds two new LXC-specific mount flags:

• create=dir (will do a mkdir_p on the path)

• create=file (will do a mkdir_p on the dirname + a fopen on the path)

This was motivated by some of the needed bind-mounts for the unprivileged containers.

Solution 2

In /var/lib/lxc/Solr4StandAlone/config add a line reading:

lxc.mount.entry = /mnt/ssd/solr_data  /var/lib/lxc/Solr4StandAlone/rootfs/data none bind 0 0

Then lxc-stop stop your container and lxc-start your container again.

That is all that is needed.

ref: reference link

Solution 3

I had to create the /data folder in the local container before the mount would work properly.

I also used this fstab entry:

/mnt/ssd/solr_data      /var/lib/lxc/Solr4StandAlone/rootfs/data        none   bind     0       0

Solution 4

As of 2015/09/30 a change resulting from a security patch breaks mounting to an absolute path with lxc.mount.entry in the config file.

Instead you can use a relative path

 lxc.mount.entry = /mnt/ssd/solr_data data none bind 0 0

See: https://wiki.debian.org/LXC#Bind_mounts_inside_the_container

Solution 5

As LXC has changed over time this can be very simple, but it stumped me for a bit, so wanted to contribute. I also created a gist for this so i can remember myself, but simply using lxc config device will do the trick.

sudo lxc config device add Solr4StandAlone sdb disk source=/var/lib/lxc/Solr4StandAlone/rootfs/data path=mnt/ssd/solr_data

Note It is important to leave the front slash off the path argument due to a change mentioned by @biscuitNinja

Mounting directories from container to host

View more solutions

Comments

[0xC0000022L]

What version of mount does this apply to? I couldn't find the option described in mount(8) on Ubuntu 14.04, for example.

[0xC0000022L]

Also not in the latest mount(8)

[little-dude]

indeed... looks like it works with lxc only. See this thread on lxc-devel ML

[Huygens]

Your solution should get better review as it works with unprivileged LXC containers tool. The other ones won't work in this case. And probably selinux/apport would need to be tweaked to allow their method. +1 for your solution!

[alok chauve]

Great addition, it works as an answer, it'll get upvoted so people see it soon. Thanks for adding to it!

[imz -- Ivan Zakharyaschev]

bind mount option is something that was missing in the OP. I believe it is the most important correction (present also in all the other working answers).

[0_0]

The ubuntu manpage has a nice example: lxc config device add [<remote>:]container1 <device-name> disk source=/share/c1 path=opt, where source is on the host machine and path lies within the container.