Mounting filesystems

Mounting filesystems within a VE

To mount filesystems inside a VE, you have several choices:

• NFS (the VE will be an NFS Client) - see NFS
• FUSE - see FUSE
• Bind mount from Hardware Node

Bind mount from Hardware Node

Recent Linux kernels support an operation called 'bind mounting' which makes part of a mounted filesystem visible at some other mount point. See 'man bind' for more information.

Bind mounts can be used to make directories on the hardware node visible to the VE.

OpenVZ uses two directories. Assuming our VE is numbered 777, these directories are:

$VZROOT/private/777
$VZROOT/root/777

Note: $VZROOT is usually /vz, on Debian systems however this is /var/lib/vz. In this document this is further referred to as $VZROOT -- substitute it with what you have.

The $VZROOT/private directory contains root directory contents. This directory or subdirectory may be symlinked onto a different file system, for example:

 $VZROOT/private -> /mnt/openvz

Putting VE root directories onto a separate file system (not the hardware node root file system) is good storage management practice. It protects the Hardware Node root file system from being filled up by a VE; this could cause problems on the Hardware Node.

Requirement

On the HN we have a directory /home which we wish to make available (shared) to all containers.

You would think that you could bind mount this directory, as in: mount --bind /home $VZROOT/private/777/home but this does not work — the contents of /home cannot be seen within the VE.

This is where the second directory listed above ($VZROOT/root/777) is used. If a VE is not started, this directory is empty. But after starting a VE, this directory contains what the VE sees as its mounted file systems.

The correct command to issue on the HN is:

 mount --bind /home $VZROOT/root/777/home

The VE must be started and the destination directory must exist. The VE will see this directory mounted like this:

# df
Filesystem           1K-blocks      Used Available Use% Mounted on
simfs                 10485760    298728  10187032   3% /
tmpfs                   484712         0    484712   0% /lib/init/rw
tmpfs                   484712         0    484712   0% /dev/shm
ext3                 117662052 104510764   7174408  94% /home