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Recent Linux kernels support an operation called 'bind mounting' which makes part of a mounted filesystem visible at some other mount point. See 'man mount' for more information.
== Filesystem layout ==OpenVZ uses two directories. Assuming our container This is numbered 777, these directories are: * <code>VE_PRIVATE</code>: $VZDIR/private/777* <code>VE_ROOT</code>: $VZDIR/root/777 {{Note|<code>$VZDIR</code> is usually <code>/vz</code>, on Debian systems however this is <code>/var/lib/vz</code>. In this document this is further referred to as <code>$VZDIR</code> -- substitute it with what how you have.}} <code>VE_PRIVATE</code> is a place for all the container files. <code>VE_ROOT</code> is the mount point to which <code>VE_PRIVATE</code> is mounted during container start (or when you run <code>vzctl mount</code> {{Warning|If you want to do a bind mount for container, you need to 'can make host system''use s <code>VE_ROOT</code>''' (not <code>VE_PRIVATE<mnt/code>!) and '''make sure that container is mounted''' (this can be checked using <code>vzctl statusdisk</code>).}} == Manual mount example == On the HN we have a directory <code>/home</code> which we wish to make available (shared) to a container 777. The correct command to issue on the HN is:<source lang="bash"> mount --bind /home $VZDIR/root/CTID=777/home The container must be started (or at least mounted) and the destination directory must exist. The container will see this directory mounted like this:
echo '# df!/bin/bash. /etc/vz/vz.conf Filesystem 1K. ${VE_CONFFILE}SRC=/mnt/diskDST=/mnt/diskif [ ! -blocks Used Available Use% Mounted one ${VE_ROOT}${DST} ]; then mkdir -p ${VE_ROOT}${DST}; fi mount -n -t simfs 10485760 298728 10187032 3% ${SRC} ${VE_ROOT}${DST} -o ${SRC}' > / ext3 117662052 104510764 7174408 94% etc/vz/conf/home${CTID}.mount
During the container stop vzctl unmounts that bind mount, so you have to chmod +x /etc/vz/conf/${CTID}.mount it again when you start the container for the next time. Luckily there is a way to automate it.</source>
== Make the If you want read-only mount persistent ==, add <code>-r</code> option to mount command.
Put a mount script in OpenVZ configuration {{Note|When specifying destination directory (<code>/etc, always use /vz/confroot/</code>) with the name <code>''CTID''or ${VE_ROOT} env.mountvariable </codenowiki> (where <code>''CTID''avoid using /vz/private)</codenowiki> is }}{{Note|When binding directories from one container IDto another, like 777). This script will be executed every time make sure you run <code>vzctl mount<have proper boot order (See [[Man/code> or <code>vzctl start</code> for a particular container. If you need to the same for all containers, use the global mount script named <code>vps.mount</code>8|BOOTORDER]] param.)}}
From any mount script you can use the following environment variables:
* <code>${VEID}</code> -- container ID (like <code>777</code>).
* <code>${VE_CONFFILE}</code> -- container configuration file (like <code>/etc/vz/conf/777.conf</code>)
Now, in order to get the value of <code>VE_ROOT</code> '''Instruction above will not work on OpenVZ 7 until you need to source both the global OpenVZ configuration file, and then the container configuration file, in that particular order. This is run the same way vzctl uses script below to determine <code>VE_ROOT</code>.enable Bind mounts:'''
=== Mount script example ===Here is an example of such a mount script (it can either be <code>chmod +x /etc/vz/conf/vps.mount</code> or <code>/etc/vz/conf/''CTID''.mount</code>) #!/bin/bash source /etc/vz/vz.conf source ${VE_CONFFILE} mount --bind /mnt/disk ${VE_ROOT}/mnt/disk === Unmount script example ===For unmounting a filesystem, <code>/etc/vz/conf/vps.umount</code> or <code>/etc/vz/conf/''CTID''.umount</code> script can be used in the same way: #!/bin/bash source /etc/vz/vz.conf source ${VE_CONFFILE} umount ${VE_ROOT}/mnt/disk {{Note|<code>''CTID''.umount</code> script is not strictly required, since vzctl tries to unmount everything on CT stop. But you'd better have it anyway.}} == Read-only bind mounts == Since Linux kernel 2.6.26, bind mounts can be made read-only. The trick is to first mount as usual, and then remount it read-only: mount --bind /home $VZDIR/root/777/home mount --bind -oremount,ro $VZDIR/root/777/home
Better wording to clarify that the additional script is not a replacement for the one above, but rather needs to be run first.
Bind mounts can be used to make directories on the hardware node visible to the container.
<source lang="bash">
cat <<'EOF' > /etc/vz/conf/vps.mount
#!/bin/bash
. ${VE_CONFFILE}
VE_MOUNT=$(echo ${VE_CONFFILE} | sed 's/\.conf$/.mount/')
[ -x ${VE_MOUNT} ] && . ${VE_MOUNT}
exit 0
EOF
== See also ==
* {{Man|vzctl|8}} (ACTION SCRIPTS section)
* [[NFS]]
* [[FUSE]]
* [[Mounting filesystems]]
[[Category:HOWTO]]