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'

little-dude · Accepted Answer · 2014-06-18T19:35:58.273

21

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.

edited Jun 18 '14 at 19:35

answered Jun 02 '14 at 17:23

little-dude

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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 Jun 02 '14 at 17:27
Also not in the [latest `mount(8)`](http://man7.org/linux/man-pages/man8/mount.8.html) – 0xC0000022L Jun 02 '14 at 17:47
2

indeed... looks like it works with lxc only. See [this thread on lxc-devel ML](https://lists.linuxcontainers.org/pipermail/lxc-devel/2013-December/006444.html) – little-dude Jun 18 '14 at 19:33

score 18 · Answer 2 · edited Jan 31 '20 at 13:41

18

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

edited Jan 31 '20 at 13:41

Luc

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answered Aug 03 '15 at 16:00

Mausy5043

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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! – Huygens Oct 01 '15 at 14:04

score 12 · Answer 3 · edited Jun 16 '16 at 14:22

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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

edited Jun 16 '16 at 14:22

Pierre.Vriens

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answered Nov 11 '15 at 13:53

biscuitNinja

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Great addition, it works as an answer, it'll get upvoted so people see it soon. Thanks for adding to it! – David Parks Nov 11 '15 at 19:22

score 11 · Answer 4 · answered Mar 25 '13 at 13:38

11

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

answered Mar 25 '13 at 13:38

David Parks

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`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). – imz -- Ivan Zakharyaschev Aug 16 '16 at 09:16

score 7 · Answer 5 · answered Aug 18 '16 at 15:03

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

The ubuntu manpage has a nice example: `lxc config device add [:]container1 disk source=/share/c1 path=opt`, where `source` is on the host machine and `path` lies within the container. — 0_0, Sep 05 '21 at 11:54

score 1 · Answer 6 · edited Dec 04 '15 at 10:47

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If you are using libvirt to create your lxc container, you can make the directory on the host to be passthrough as shown here:

root@localhost:/# cat /etc/libvirt/lxc/my_container.xml
...
 <filesystem type='mount' accessmode='passthrough'>
    <source dir='<dir on host>'/>
    <target dir='<dir on container>'/>
 </filesystem>
....

edited Dec 04 '15 at 10:47

Kevdog777

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answered Dec 04 '15 at 10:21

Swanand Pashankar

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

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