Physical to container

A rough description of how to migrate existing physical server into a VE.

Prepare a new “empty” VE

For OpenVZ this would mean the following (assume you chose VE ID of 123):

mkdir /vz/root/123 /vz/private/123
cat /etc/vz/conf/ve-vps.basic.conf-sample > /etc/vz/conf/123.conf

Preparing to migrate

Stop most services on a machine to be migrated. “Most” means services such as web server, databases and the like — so you will not loose your data. Just leave the bare minimum (including ssh daemon).

Copying the data

Copy all your data from the machine to an OpenVZ box. Say you'll be using VE with ID of 123, then all the data should be placed to /vz/private/123/ directory (so there will be directories such as /vz/private/123/bin, etc, var and so on). This could be done by scp or rsync.

rsync example (run from the new HN):

rsync -arvpz --exclude dev --exclude proc --exclude tmp -e "ssh -l root@a.b.c.d" root@a.b.c.d:/ /vz/private/123/

Advantage: Your system doesn't really go down.

Another way to do is using a live cd, booting up and use tar to dump the complete disk in a tar you save over the network or on a USB device.

Another approach is using tar and excluding some dirs, you could do it like this:

Create a file /tmp/excludes.excl with these contents:

.bash_history
/dev/*
/mnt/*
/tmp/*
/proc/*
/sys/*
/usr/src/*

Then create the tar. But remember, when the system is 'not' using udev, you have to look into /proc/ after creating your VE because some devices might not exist. (/dev/ptmx or others)

# tar cjpf /tmp/mysystem.tar.bz2 / -X /tmp/excludes.excl

Naturally, you can only do this when the critical services (MySQL, apache, ..) are stopped and your /tmp filesystem is big enough to contain your tar.

Advantage: You don't need to boot from a livecd, so your system doesn't really go down.

Set VE parameters

OSTEMPLATE

You have to add OSTEMPLATE=xxx line to /etc/vz/conf/123.conf file, where xxx would be distribution name (like debian-3.0) for vzctl to be able to make changes specific for this distribution.

IP address(es)

Also, you have to supply an IP for a new VE:

vzctl set 123 --ipadd x.x.x.x --save

Making adjustments

Since VE is a bit different than a real physical server, you have to edit some files inside your new VE.

/etc/inittab

A VE does not have real ttys, so you have to disable getty in /etc/inittab (i. e. /vz/private/123/etc/inittab).

sed -i -e '/getty/d' /vz/private/123/etc/inittab

/etc/mtab

Link /etc/mtab to /proc/mounts:

rm -f /vz/private/123/etc/mtab
ln -s /proc/mounts /vz/private/123/etc/mtab 

/etc/fstab

Since you do not have any real disk partitions in a VE, /etc/fstab (or most part of it) is no longer needed. Empty it (excluding the line for /dev/pts):

cp /vz/private/123/etc/fstab /vz/private/123/etc/fstab.old
grep devpts /vz/private/123/etc/fstab.old > /vz/private/123/etc/fstab

You can also mount a devpts in a running (but not fully functional) VE:

vzctl exec 123 mount -t devpts none /dev/pts

/dev TTY devices

In order for vzctl enter to work, a VE need to have some entries in /dev. This can either be /dev/ttyp* and /dev/ptyp*, or /dev/ptmx and mounted /dev/pts.

/dev/ptmx

Check that /dev/ptmx exists. If it does not, create with:

mknod /vz/private/123/dev/ptmx c 5 2

/dev/pts/

Check that /dev/pts exists. It's a directory, if it does not exist, create with:

mkdir /vz/private/123/dev/pts

/dev/ttyp* and /dev/ptyp*

Check that /dev/ttyp* and /dev/ptyp* files are there. If not, you have to create those, either by using /sbin/MAKEDEV, or by copying them from the host system.

To copy:

cp -a /dev/ttyp* /dev/ptyp* /vz/private/123/dev/

To recreate with MAKEDEV, either

/sbin/MAKEDEV -d /vz/private/123/dev ttyp ptyp

or

cd /vz/private/123/dev && /sbin/MAKEDEV ttyp

Other

There might be other adjustments needed. Please add those here if you have more info.

Starting a new VE

Try to start your new VE:

vzctl start 123

Now check that everything works fine. If not, see #Troubleshooting below.

Troubleshooting

Can't enter VE

If you can not enter your VE (using vzctl enter), you should be able to at least execute commands in it.

First, see the #/dev TTY devices section above.

Next, check if devpts is mounted:

vzctl exec 123 mount | grep pts

If it is not mounted, mount it:

vzctl exec 123 mount -t devpts none /dev/pts

Then, add the appropriate mount command to VE's startup scripts. On some distros, you need to have the appropriate line in VE's /etc/fstab.

Other problems

If anything goes wrong, try to find out why and fix. If you have enough Linux experience, it can be handled. Also check out IRC and please report back on this page.

Success Stories

- Debian 3.1 Sarge with MySQL, apache2, PowerDNS --stoffell 08:41, 8 February 2007 (EST)