If you get the error “/dev/zero: No space left on device” in the apache error.log on a OpenVZ virtual machine, then the shared memory size in the xcache.ini is too high or the xcache.mm_path is set wrong.

Edit the file /etc/php5/conf.d/xcache.ini

vi /etc/php5/conf.d/xcache.ini

xcache.mmap_path = "/tmp/xcache"

/etc/init.d/apache2 restart

If the roor still occurs after some time, you will have to reduce the xcache.size.

Edite the xcache.ini file:

vi /etc/php5/conf.d/xcache.ini

xcache.size  =                8M

/etc/init.d/apache2 restart

The /tmp and /dev/shm directories of a OpenVZ virtual machine shall be mounted without suid and exec permissions. To achieve this, create a a shell script on the host server for every virtual machine which contains the commands to remount the directories. This script will be started automatically by openvz when the VM is started.

I will use VPSID as placeholder for the ID of the virtual machine in the commands and the script. Replace VPSID with the id of the virtual machine that you want to create the script for, e.g. replace VPSID with 101.

Create the script:

vi /etc/vz/conf/VPSID.mount

#!/bin/bash
mount -n --bind -onosuid,noexec /vz/vps/VPSID/tmp /vz/root/VPSID/tmp
mount -n --bind -onosuid,noexec /vz/vps/VPSID/shm /vz/root/VPSID/dev/shm
exit ${?}

chmod 700 /etc/vz/conf/VPSID.mount

In case you plan to virtualize your server infrastructure and migrate physical servers to OpenVZ virtual machines, you may find this tutorial helpful:

http://wiki.openvz.org/Physical_to_container

I used this to migrate a ISPConfig Debian system to OpenVZ successfully.

Vzdump is a perl script that makes live backups of OpenVZ virtual machines very easy. The following steps are for Debian Linux but vzdump can be used on all other linux distributions. Only the installation may vary.

Download and install vzdump from http://download.openvz.org/contrib/utils/vzdump/

cd /tmp
wget http://download.openvz.org/contrib/utils/vzdump/vzdump_1.1-2_all.deb
dpkg -i vzdump_1.1-2_all.deb

Create the backup directory
<p class="command">mkdir /home/backup

Create a backup of all virtual machines as compressed (tar.gz) archive and send a email report to the root user when finished.

vzdump --dumpdir /home/backup --suspend --compress --mailto root --all

vzdump can also be used to restore a backup.  Example: restore the backup of the virtual machine 101:

vzdump --restore /home/backup/vzdump-101.tgz 101

To restore the backup to a different virtual machine, you can specify a differnt target ID. E.g. restore the backup of vm 101 to the virtual machine with the ID 500:

vzdump --restore /home/backup/vzdump-101.tgz 500