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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 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 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 container 777. The correct command to issue on the HN is: mount --bind /home $VZDIR/root/777/home The container must be started (or at least mounted) and the destination directory must exist. The container will see this directory mounted like this: # df Filesystem 1K-blocks Used Available Use% Mounted on simfs 10485760 298728 10187032 3% / ext3 117662052 104510764 7174408 94% /home During the container stop vzctl unmounts that bind mount, so you have to mount it again when you start the container for the next time. Luckily there is a way to automate it. == Make the mount persistent == Put a mount script in OpenVZ configuration directory (<code>/etc/vz/conf/</code>) with the name <code>''CTID''.mount</code> (where <code>''CTID''</code> is container ID, like 777). This script will be executed every time you run <code>vzctl mount</code> or <code>vzctl start</code> for a particular container. If you need to the same for all containers, use the global mount script named <code>vps.mount</code>. From any mount script you can use the following environment variables:* <code>${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> you need to source both the global OpenVZ configuration file, and then the container configuration file, in that particular order. This is the same way vzctl uses to determine <code>VE_ROOT</code>. lang=== Mount script example ===Here is an example of such a mount script (it can either be <code>/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 -n --bind /mnt/disk ${VE_ROOT}/mnt/disk After creating script please make it executable by issuing "chmod +x CTID.mount" at command line otherwise vm fails to start === 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.}} umount scripts could cause trouble and errors on VM start and might not be required if using the -n option on mount. [http://forum.openvz.org/index.php?t=msg&goto=37800&&srch=using+-n+and+no+umount+script#msg_37800 read forum post] When mounting whitout <code>-n</code> option, <code>umount</code> script become required, but display errors,because of recursivity of umount procedure initiated before by libvzctl.777
Even echo '#!/bin/bash. /etc/vz/vz.conf. ${VE_CONFFILE}SRC=/mnt/diskDST=/mnt/diskif no option <code>[ ! -e ${VE_ROOT}${DST} ]; then mkdir -p ${VE_ROOT}${DST}; fimount -n</code> was specified at mount, and no <code>umount</code> script was run,-t simfs ${SRC} ${VE_ROOT}${DST} -o ${SRC}system file <code' >/etc/mtab<vz/conf/code> could become wrong in the HN, causing trouble to commands like df${CTID}.mount
== Read-only bind mounts ==chmod +x /etc/vz/conf/${CTID}.mount</source>
Since Linux kernel 2.6.26, bind mounts can be made If you want read-only. The trick is to first mount as usual, and then remount it readadd <code>-only:r</code> option to mount command.
mount -n --bind {{Note|When specifying destination directory, always use /home vz/root/ or $VZDIR{VE_ROOT} env. variable <nowiki>(avoid using /rootvz/777private)</homenowiki>}} mount -n --bind -oremount{{Note|When binding directories from one container to another,ro $VZDIR/root/777make sure you have proper boot order (See [[Man/homevzctl.8|BOOTORDER]] param.)}}
With some kernels you need to add the sourcedirectory also: mount -n --bind -oremount,ro '''/home''' $VZDIR/root/777/home
Sometimes it is usefull to have a folder read-only mounted in a VPS, but also be able to put files in that directory. If '''Instruction above will not work on OpenVZ 7 until you want that, just create an other directory and simlink run the read only files into that folderscript below to enable Bind mounts:'''
vzctl exec2 777 <source lang="mkdir bash">cat <<'EOF' > /etc/vz/addfileshere && ln -conf/vps.mount#!/bin/bash. ${VE_CONFFILE}VE_MOUNT=$(echo ${VE_CONFFILE} | sed 's /home\.conf$/* .mount/addfileshere/"')[ -x ${VE_MOUNT} ] && . ${VE_MOUNT}exit 0EOF
Now the chmod +x /addfileshere folder is fully writable and it even feels like it is possible to delete files (but that are only the simlinks)etc/vz/conf/vps.mount</source>
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.
== See also ==
* {{Man|vzctl|8}} (ACTION SCRIPTS section)
* [[NFS]]
* [[FUSE]]