Physical to container
A rough description of how to migrate existing physical server into a container.
Contents
- 1 Preparing to migrate
- 2 Prepare a new “empty” container
- 3 Copying the data
- 4 Setting container parameters
- 5 Making adjustments
- 6 Starting a new container
- 7 Troubleshooting
- 8 Scripting
- 9 Success stories
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 lose your data. Just leave the bare minimum (including ssh daemon).
To make things easier you may like to first follow the basic instructions elsewhere and create a dummy container based on the same Linux distribution you want to migrate. That way you can take that dummy as a template and then copy to your new migrated container and modify. You can later discard this dummy.
Prepare a new “empty” container
For OpenVZ this would mean the following (assume you chose CT ID of 123):
mkdir /vz/root/123 /vz/private/123
cat /etc/vz/conf/ve-basic.conf-sample > /etc/vz/conf/123.conf
Note: Now comes the dummy container handy mentioned above: Simply copy the xxx.conf file of the dummy to your new yyy.conf and modify it. |
Note: If you have created a container from the same distro as the basis for the migration, simply take not of the CT ID and skip this step. |
Copying the data
Copy all your data from the machine to an OpenVZ box. Say you'll be using container 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 in several ways:
rsync
On the new HN create a file /tmp/exclude.txt
with:
/tmp /boot /lib/modules /etc/blkid /etc/mtab /etc/lvm /etc/fstab /etc/udev
and run rsync as follows:
rsync -avz -H -X --one-file-system --numeric-ids --exclude-from=/tmp/exclude.txt -e ssh root@a.b.c.d:/ /vz/private/123/
Note: You should add the -H option, so hardlinks will be preserved during sync and also include the -X option to preserve file extended attributes
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If your source system have multiple partitions (for example /var
or /home
) repeat the command above for each partition in your system; for example:
rsync -avz -H -X --one-file-system --numeric-ids -e ssh root@a.b.c.d:/var/ /vz/private/123/var/
Advantage: Your system doesn't really go down.
Live CD
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.
Tar
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 container because some devices might not exist. (/dev/ptmx or others)
# tar --numeric-owner -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 live cd, so your system doesn't really go down.
Setting container 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.
Note: If you copied from the dummy container or are using it as basis for your migrated system then this step is already accomplished. |
IP address(es)
Also, you have to supply an IP for a new container:
vzctl set 123 --ipadd x.x.x.x --save
venet vs. veth
You may use veth interface instead of venet if you need just bring old server up for seamless migration of services. It may be nessessary if server you are migrating is badly configured and it is hard to find all hard-coded net interfaces settings and so on.
veth inteface may be included into bridge to allow seamless old installation access.
Making adjustments
Since container is a bit different to a real physical server, you have to edit some files inside your new container.
/etc/inittab
A container does not have real ttys, so you have to disable getty in /etc/inittab
(i. e. /vz/private/123/etc/inittab
).
sed -i -e 's/^[0-9].*getty.*tty/#&/g' /vz/private/123/etc/inittab
/etc/mtab
Link /etc/mtab
to /proc/mounts
, for df
to work properly:
ln -sf /proc/mounts /vz/private/123/etc/mtab
/
) is mounted not from the container itself, but rather from the host system. That leaves /etc/mtab
in container without a record for /
being mounted, thus df doesn't show it. By linking /etc/mtab → /proc/mounts
we make sure /etc/mtab shows what is really mounted in a container.
Sure this is not the only way to fix df; you can just manually add a line to /etc/mtab
telling /
is mounted, and make sure this line will be there after a reboot./etc/fstab
Since you do not have any real disk partitions in a container, /etc/fstab (or most part of it) is no longer needed. Empty it (excluding the lines for /dev/pts
, /proc
, /sys
and such):
mv /vz/private/123/etc/fstab /vz/private/123/etc/fstab.old
egrep '/dev/pts|/dev/shm|/proc|/sys' /vz/private/123/etc/fstab.old > /vz/private/123/etc/fstab
You can also mount a devpts in a running (but not fully functional) container:
vzctl exec 123 mount -t devpts none /dev/pts
A still better approach would be simply to copy the /etc/fstab
from a previously created container from a template of the same or similar distribution. In the case of RedHat/CentOS 5 this is:
none /dev/pts devpts rw 0 0
and for RedHat/CentOS 6:
none /dev/pts devpts rw,gid=5,mode=620 0 0
/dev
Note: Once again if you are using the container from the same distro as basis, and you were carefull to not overwrite /dev with rsync by using the --one-file-system option, you can skip this section
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Introduction: static /dev
In order for container to work, some nodes should be present in container's /dev
. For modern distributions, udev is taking care of it. For a variety of reasons udev doesn't make much sense in a container, so the best thing to do is to disable udev and create needed device nodes manually.
Note that in some distributions /dev
is mounted on tmpfs
— this will not work in case of static /dev
. So what you need to do is find out where /dev
is being mounted on tmpfs
and remove this. This is highly distribution-dependent; please add info for your distro here.
For Suse 11.0, It is found in /etc/init.d/boot
After you made sure your /dev
is static, populate it with needed device nodes.
Please pay attention to the access permissions of the device files being created: a default file mode for newly created files is affected by umask
(w:umask). You can use --mode option for mknod
to set the desired permissions.
Note: Now comes the dummy container handy mentioned above: Simply copy the entire /dev directory of the dummy to your new migrated container - worked in my case at least with Debian Etch. |
tty device nodes
In order for vzctl enter to work, a container needs 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 --mode 666 /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
/dev/null
Make sure sure /dev/null is not a file or directory; if unsure remove and recreate. If this is not correct sshd will not start correctly.
rm -f /vz/private/123/dev/null mknod --mode 666 /vz/private/123/dev/null c 1 3
/dev/urandom
Check that /dev/urandom exists. If it does not, create with:
mknod --mode 444 /vz/private/123/dev/urandom c 1 9
Using udev anyway
CentOS 5 can run in a container with udev enabled. You need to create /etc/udev/devices, containing the above device nodes. Also, the following will create the extra device nodes you need
mkdir /vz/private/123/etc/udev/devices /sbin/MAKEDEV -d /vz/private/123/dev {p,t}ty{a,p}{0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f} console core full kmem kmsg mem null port ptmx random urandom zero ram0 /sbin/MAKEDEV -d /vz/private/123/etc/udev/devices {p,t}ty{a,p}{0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f} console core full kmem kmsg mem null port ptmx random urandom zero ram0
/proc
Note: One more time you may skip this if you are using a container created from a template of the same distro as your basis system. |
Make sure the /proc directory exists:
ls -la /vz/private/123/ | grep proc
If it doesn't, create it:
mkdir /vz/private/123/proc
/etc/init.d services
Some system services can (or in some cases should) be disabled and/or uninstaled. A few good candidates are:
- acpid, amd (not needed)
- checkfs, checkroot (no filesystem checking is required in container)
- clock (no clock setting is required/allowed in container)
- consolefont (container does not have a console)
- hdparm (container does not have real hard drives)
- klogd (unless you use iptables to LOG some packets)
- keymaps (container does not have a real keyboard)
- kudzu (container does not have real hardware)
- lm_sensors (container does not have access to hardware sensors)
- microcodectl (container can not update CPU microcode)
- netplugd (container does not have real Ethernet device)
- irqbalance (this is handled in host node)
- auditd ( not needed in container)
- lvm2-monitor (no LVM in containers)
- ntp/ntpd (clock taken from host node)
To see which services are enabled:
- RedHat/Fedora/SUSE:
/sbin/chkconfig --list
- Debian: Use '
rcconf
' (ncurses) orupdate-rc.d
( See: http://www.debianadmin.com/manage-linux-init-or-startup-scripts.html )
- Gentoo:
/sbin/rc-update show
To disable the service:
- RedHat/Fedora/SUSE:
/sbin/chkconfig SERVICENAME off
- Debian:
' update-rc.d -f hdparm remove '
- Gentoo:
/sbin/rc-update del SERVICENAME
Disable old network interface
You should disable your old physical network interface from starting at boot time. This is distribution-dependant.
Fedora/CentOS/Red Hat
Edit /vz/private/{CTID}/etc/sysconfig/network-scripts/ifcfg-ethx
Make the following look like this:
ONBOOT=no
If the files /vz/private/{CTID}/etc/sysconfig/network-scripts/ifdown-venet or /vz/private/{CTID}/etc/sysconfig/network-scripts/ifup-venet exist, make sure they won't be used. These two files might exist if the physical server had OpenVZ installed. One way to do this is to rename them, like so:
mv ifdown-venet SKIP.ifdown-venet
Failing to do this will prevent networking from starting up correctly in the container.
Debian/Ubuntu
Edit /etc/network/interfaces
# /etc/network/interfaces -- configuration file for ifup(8), ifdown(8) # The loopback interface # automatically added when upgrading auto lo eth0 iface lo inet loopback iface eth0 inet static address 10.0.0.4 netmask 255.0.0.0 network 10.0.0.0 broadcast 10.0.0.255
You can either comment out the eth* interface stanza(s), or take it out of the "auto" line(s).
Ubuntu server 8.x
Here what I have done for my Ubuntu server JEOS 8.04.2
rm /vz/private/123/etc/network/if-up.d/ntpdate rm /vz/private/123/etc/event.d/tty{1,2,3,4,5,6} vzctl exec 123 update-rc.d -f klogd remove vzctl exec 123 update-rc.d -f udev remove
openSUSE/SLES
Use Yast.
Disable udev if you create DEVNODES devices
If you are creating devices for the container with a DEVNODES statement in a veid.conf file then these devices may be overwritten/deleted by udev when the container starts. As udev cannot "see" the device from within the container it disables it. Therefore, if you have DEVNODES statements in veid.conf then disable udev.
In Fedora, Redhat, Centos, try commenting out any udev entries in /vz/private/{CTID}/etc/rc.sysinit Comment the line similar to this:
#[ -x /sbin/start_udev ] && /sbin/start_udev
Other adjustments
There might be other adjustments needed. Please add those here (just above this section) if you have more info.
Starting a new container
Try to start your new container:
vzctl start 123
Now check that everything works fine. If not, see #Troubleshooting below.
Troubleshooting
PHP not serving pages / random issues
Make sure that /tmp and /var/tmp are created if you rsynced over your data and that they have proper permissions
mkdir tmp chmod 1777 tmp
Can't enter container
If you can not enter your container (using vzctl enter
), you should be able to at least execute commands in it.
First, see the #tty device nodes 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 container's startup scripts. On some distros, you need to have the appropriate line in container's /etc/fstab.
In Fedora, try commenting out any udev entries in /vz/private/{CTID}/etc/rc.sysinit
vi /vz/private/{CTID}/etc/rc.sysinit
Locate the udev entry from within vim
/udev
Then comment the line similar to this:
#[ -x /sbin/start_udev ] && /sbin/start_udev
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.
Scripting
For CentOS below are two scripts to help with the migration:
- pre-copy.sh: Does the necessary configuration required for the migration of a server/VM to a CT.
- post-copy.sh: Performs steps 5 and 6.
Success stories
Note: please add your line to the bottom of this list, and do not forget to sign it using --~~~~
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- Debian 3.1 Sarge with MySQL, apache2, PowerDNS --stoffell 08:41, 8 February 2007 (EST)
- Red Hat 7.2 with MySQL 3.23, apache, Chilisoft --stoffell 13:26, 9 February 2007 (EST)
- Gentoo with Courier, Postfix, MySQL, Apache2 --bfrackie 19:00, 18 March 2007 (EST)
- AltLinux Master with qmail, MySQL, Apache, etc - to Debian/testing with OpenVZ --alexkuklin 16:16, 23 March 2007 (EST)
- Centos 4.4 with apache2, SVN, TRAC, etc. --bitherder 23:38, 26 February 2008 (EST)
- Centos 4.6 with apache2, Tomcat 5.0.x, postgresql, etc on CentOS 5.1 64bit Host --laslos 17:35, 10 March 2008 (EST)
- Debian Etch with apache2 etc... on CentOS 4.6 Host --laslos 19:46, 10 March 2008 (EST)
- Debian 1:3.3.5-13 with apache2, PHP, etc. --spawrks 23:36, 10 April 2008 (EST)
- Debian Etch with apache2, MySQL, etc. --zhafrance 16:29, 20 April 2008 (EST)
- Debian Etch i386 with apache2, MySQL, etc. --geejay 17:29, 26 May 2008 (GMT)
- Centos 4.6 with apache2, MySQL, Qmail etc. --Bharathchari 08:06, 13 June 2008 (EDT)
- Centos 4.6 with cPanel/WHM (Apache2, Mysql, Exim, etc) --Zccopwrx 08:16, 30 July 2008 (EDT)
- SlackWare 10.1 (Qmail) --defiancenl
- SlackWare 10.0 (Qmail) --defiancenl
- Ubuntu 8.04.3 LTS JEOS (Apache2, Mysql) --bougui Fri Aug 28 10:40:41 EDT 2009
- CentOS 5.3 (Apache2, Mysql, Cacti) --kofl September 12 2009
- Scientific Linux 3.0.9 (Macrovision FLEXlm) —The preceding unsigned comment was added by 137.226.90.94 (talk • contribs) 11:34, 4 November 2009.
- Red Hat Enterprise Linux 4 (rhel4) --Bpuklich 17:20, 15 February 2010 (UTC)
- Debian SID up-to-date with apache2, MySQL, posgrey etc. --nyquist 14:04, 06 July 2010 (UTC)
- Centos 5.x with Plesk -- 05:33, 17 August 2010 (UTC)
- Redhat 4 -- 20:32, 18 August 2010 (UTC)
- Fedora 4 -- 15:06, 20 August 2010 (UTC)
- Fedora 9 x64 with FDS and samba PDC --burn 23:20 10 October 2010
- Fedora 3 x32 with Plesk -- 23 October 2010 --Rex Wickham (2020media.com) 13:15, 23 October 2010 (UTC)
- Debian 6 (Squeeze) with Lighttpd, MySQL, nfs, smb, etc. --95.21.175.189 22:39, 30 July 2011 (UTC)
- RedHat 9 (Shrike) with apache,nginx,mysql,qmail 09 August 2011 (UTC)
- Centos 5.6 with Postresql and JitterBit 24 August 2011
- Centos 4.9 with MySQL, Apache, ColdFusion, etc. 26 August 2011
- Centos 5.6 with MySQL, Apache, BIND, Postfix, Mono, etc. 26 August 2011
- Centos 5.7 with MySQL, Apache, Nginx, Memcached, Postfix, Openx, etc. --Juranas 18 November 2011
- RedHat Enterprise Linux 5 (rhel 5.6 - x86_64) 14:50, 18 November 2011
- Debian 6.0.4 with DTC Hosting Contro Panel . 15:00, 14 May 2012
- Debian 6, LAMP with ISPManager CP (no adjustments were made, just transferred the file structure and created ctid.conf) 03:19, 15 Jun 2012
- Debian 5.0.3, with Mysql, Apache, ISCP omega, Postfix, etc --91.143.222.253 19:47, 28 June 2012 (EDT)