How To Image FreeBSD Systems Using ``tbku``
This document describes how to use the TundraWare Inc. ``tbku``
utility to "image" or "clone" FreeBSD systems.
What follows is a description of activities that can (and
will) clobber the contents of a hard drive. Never do any
of this until you understand what's going on fully.
Obviously, you should have backups of whatever machine
you're targeting so that if (when) you make a mistake, you
can recover your data. YOU HAVE BEEN WARNED! If you
proceed, you do so at your own risk ... and no, I will
*not* come to your house and help you recover your hard
Why Bother Imaging?
Suppose we need to build a new instance of a ``FreeBSD`` system.
Perhaps we need to replace one that just had a hard drive failure.
Maybe we want to build a new server that is based on our "standard"
system configuration. In other words, we want to go from "bare metal"
hardware to a fully running *and configured* system as quickly as
There are a number of commercial and open source solutions to this
problem, but they all have one thing in common: We want to minimize
the amount of manual labor needed to install, configure, and otherwise
customize the final system. This is especially important in large
data centers where it is impractical to manually (re)install each and
every server, its applications, and its customization information.
"Imaging" or "Cloning" allows us to keep a copy of the entire OS *as
configured* - that means with all its applications and configuration
options set up as desired. We then load or "Provision" a new hard
drive with this image and *voila'*, "instant" running system.
When Does Imaging NOT Make Sense?
Imaging works best when the system you are targeting is very similar
or identical to the system that made the image in the first place.
For example, Imaging is a great way to restore a single machine from
its own backups - say after a hard disk crash or upgrade.
Imaging is more complex when the source of the image and the target
machines are different. The more different they are, the harder it
will be to get the image running on the new target machine.
As a practical matter, production Data Centers tend to keep a separate
restore image around *for each different system variant*. So, for
example, you might find a separate image for IBM web servers, IBM
applications servers, Dell database servers, Toshiba laptops, and so
Imaging may- or may not make sense when initially installing a new
configuration. Say you have a system that is a web server, but you
now want to build a separate machine that is a database server.
Typically, you would initially install FreeBSD with the installation
disk, configure the database and *then* create a system image of your
database server. However, this is kind of time consuming. It might
simpler to image the target machine with your web server image, boot
it, reconfigure it as a database server, and then take an image of
your newly configured server for future installations.
What Is ``tbku``?
``tbku`` is a shell script that makes it easy to create tarballs of
some of all of your filesystems. ``tbku`` does not help you with
*restoring* your image, it's just handy for creating the image in the
If you've never used it before, take a moment to download it and read
the documentation. You'll find the latest copy at:
There is no fee for using ``tbku`` in any context, personal or
commercial. However, there are some licensing terms you have to abide
by to use it, so take a moment to read the license in the distribution
You don't *have* to use ``tbku`` to create your backup
image. The description below should work fine so long
as you have a backup of all the relevant files that
preserves all the appropriate file information such as
ownership and permissions. ``tbku`` just makes it easy
to automate the creation of such backups.
The Big Picture
Before diving into the details, it's good to get a sense of the
overall process. Imaging a system requires the following steps:
A. Create the master image:
- Create a baseline system configured as you want it.
- Take an "image" of it. (That's where ``tbku`` is helpful.)
- Save the image somewhere (DVD, USB drive, network drive ...)
you can get at when you need it to (re)install a system.
B. Use the master image to (re)provision a machine:
- Prepare the target hard disk to receive the image.
- Dump the image onto the hard disk.
- Adjust the configuration if/as needed for the new hardware.
Creating The Master Image
Unlike other approaches that make an image of *the disk*, ``tbku``
creates an image of *files* on the disk. This means that your new
target disk does not have to be physically the same as the one on
which the master image (sometimes called a "snapshot") was made. You
can clone systems back and forth between SCSI, IDE, and SATA. You can
clone from smaller disks to larger ones or go the other way.
The whole point of imaging is to avoid having to do
custom configuration for each new installation.
However, some configuration changes may be necessary
when the target environment or hardware is different
than the system on which the master image was created.
This is discussed a bit more below in the `Gotchas`_
Creating The Master Image
1. Select the machine whose existing FreeBSD installation
you want preserved or used as a standard installation image.
2. Image that system with ``tbku`` using the following
Notice that we do *not* backup the dynamic kernel-created
filesystems like ``/dev`` or ``/proc``, nor do we backup
utility mountpoints like ``/mnt`` or ``/tmp``.
Also, if you have ``tbku`` writing your backup to the local
disk, make sure that directory is *not* included in the
fileset. Doing so would create a recursive backup wherein
the backup would be copied to itself.
The exact fileset you use will vary somewhat depending on
how you've laid out your directory tree and just what you
want included in your image. Use the fileset above as a
point of departure, and tune it for your exact needs.
3. Save the resulting ``.tar.gz`` (tarball) file somewhere
it can be retrieved later when you want to image another
machine. This can be a network server, a USB drive,
a DVD or whatever makes sense in your environment. As
with all backup systems, it's pretty important to make
multiple copies of the backup image, and keep a couple
of them off-site.
Provisioning With The Master Image
Now that we have a "snapshot" or master image, we can use it to
(re)provision machines. The general idea here is to take advantage of
the tools already present on the FreeBSD installation CD. However,
instead of actually installing an operating system, we'll just use the
paritioning and disk labeling tools to prepare the target disk to
receive our FreeBSD image. Then, we'll jump into the ``Fixit`` shell
and actually do the restore from there.
Provisioning Machines With A Master Image
1. Boot the FreeBSD installation disk.
2. Prepare the disk to receive a FreeBSD filesystem::
Select the target drive
Partition as desired
Select the partition that will boot
S - To make it bootable
Select the boot manager you want
Layout your partition(s) as desired
The Automatic option is a good choice
**WRITE DOWN THE DEVICE/MOUNT ASSIGNMENTS!**
You'll need them later
W - Write the changes out (Answer "Yes" at the prompt)
Exit back to the main menu
At this point, your target disk has been partitioned,
labeled, and had the Master Boot Record installed. The copy
of FreeBSD you booted from CD is pretty smart about this.
It has already mounted your mountpoints (the ones you wrote
down above, right?) under its own ``/mnt`` directory. We'll
take advantage of this in the next step.
3. Now we're ready to actually dump the image onto our newly
prepared disk. The FreeBSD team helpfully provides a fairly
complete shell environment where we can do what is needed.
Simply select the ``Fixit`` option from the main menu, and
the ``CDROM/DVD`` suboption, and you'll find yourself in a
shell. You can prove that your new disk mountpoints are
ready to be loaded, by doing this::
You should see your newly created filesystems mounted under
``/mnt``. Now, we need to create the top level directories
that are typically not backed up in an image (some of these
may already be present)::
mkdir cdrom dev dist proc tmp
At this point, we need the image tarball file to go ahead
and do the image restore. But ... we need to take a small
detour here. You may need to do a few things to be able to
*get* to your image. The ``Fixit`` environment is purposely
fairly small (so it can run in a logical memory disk). As
such, it does not have a lot of the utilties, kernel
modules, and/or libraries you may need to get to your backup
Say, for example, your image is on as USB drive. You plug
the drive in and take a look at ``/var/log/messages`` where
you are informed that the drive has been recognized as
``/dev/da1``. So, you try this::
mount -t msdosfs /dev/da1s1 /mnt/mnt
Oops ... the ``Fixit`` shell complains - it doesn't know how
to mount filesystems of type ``msdosfs`` because the
necessary file ``/sbin/mount_msdosfs`` file is not present
in the ``Fixit`` operating environment.
Fortunately, there's a very simple way to work around this.
The CD from which you booted is itself mounted under
``/dist``. That CD has a more-or-less full "live" FreeBSD
system on it, that *does* have the files you need there. In
this case, the "fix" is to do something like this::
mkdir -p /sbin # Make sure the directory exists in Fixit
cp -pv /dist/sbin/mount_msdosfs /sbin
Now the mount command above will work fine, and you
can get to your backup tarball.
You can use a similar approach to get the necessary files
for accessing your image via sftp, nfs, and other filesystem
types. Just remember that, if you do need to use a network,
you need to initialize it first with something like::
ifconfig <NIC device name> address mask
OK, so now we've mounted the medium with our
image on it under ``/mnt/mnt``. To actually image the
new disk, all we have to do is this::
cd /mnt # Make sure we're at the
# logical root of our disk
tar -xzvf mnt/my-fine-image.tar.gz
4. Finally, we need to make sure that our newly imaged
filesystems will be mounted properly at boot time. This is
controlled by the contents of: ``/mnt/etc/fstab`` Suppose,
after we image the drive, that file looks like this::
/dev/ad4s1b none swap sw 0 0
/dev/ad4s1a / ufs rw 1 1
/dev/ad4s1d /var ufs rw 2 2
/dev/ad4s1e /usr ufs rw 2 2
/dev/acd0 /cdrom cd9660 ro,noauto 0 0
This would indicate the image was taken from a system with
FreeBSD installed on the first SATA drive. Now, lets assume
we're going to use the same slice layout, but our newly
imaged drive is the first *SCSI* drive on the system.
``/mnt/etc/fstab`` needs to be edited to look like this::
/dev/da0s1b none swap sw 0 0
/dev/da0s1a / ufs rw 1 1
/dev/da0s1d /var ufs rw 2 2
/dev/da0s1e /usr ufs rw 2 2
/dev/acd0 /cdrom cd9660 ro,noauto 0 0
It may also be necessary to edit the ``/mnt/etc/rc.conf``
file to adjust IP address assignments or other system
We're DONE! Well ... maybe. If the environment or hardware of your
target machine is similar/same as the machine from which you took the
original image OR if the kernel you plan to boot has support for your
new target hardware, you should just be able to boot and run at this
point. If not, read the following `Gotchas`_ section for further
This may all seem complex the first time you do it, but after a couple
of times, you'll be able to do this in your sleep. This is one of
those things where describing it is more complicated than just doing
Depending on how large your backup image is, a complete system restore
can typically be done in less than an hour. That's less than an hour
to a *completely configured system* with all your applications, custom
configuration, and so on as you last left them.
If you use the approach described above to reprovision the same
machine - say after a disk failure or disk upgrade - then that's all
you have to do. Your "target" machine is essentially identical to the
one from which you got the backup image ... the same machine.
However, there are circumstances where you cannot avoid doing some
configuration on the newly provisioned machine. This is the case
where there is a significant difference between the machine that took
the snapshot and the machine receiving it. This might be because the
target machine has different hardware, needs a different IP address,
uses a different chipset, and so on.
What Problems Can I Expect?
So, you've decided to image a machine that is somehow different than
the original source of the image. Here's what you'll possibly
A. Environmental Differences
Your newly imaged machine may work fine except that its environment
needs to change. The most common thing here is the need to
reconfigure the NIC with new network parameters like IP address,
netmask, DNS server, default route, and so on. Similarly, you may
want to change the machine name or domain name. This is why you
need to edit ``/mnt/etc/rc.conf`` before booting your newly imaged
Keep in mind that changing the OS environment may also require
changes in your applications' configuration. For instance,
changing your machine name, IP, and so forth can break Apache. You
may need to edit ``/mnt/etc/rc.conf`` to temporarily prevent these
applications from starting so that you can successfully boot boot
the newly imaged system. Once the system is running, you can
correct any applications' configuration that need to be changed.
B. Different Hardware
This is the tougher situation to handle after a machine has been
newly imaged. Modern FreeBSD kernels come with enough standard
driver support built-in that they should boot on most standard
hardware ... unless you've hand tuned the kernel on the machine
where the image was taken. You should therefore always build an
image with a system that has the option to boot a GENERIC kernel.
This kernel is likely to boot on almost all but the strangest
However "booting" and "running properly" are two different things.
If the hardware on your target machine is considerably different
thatn the original machine on which the image was produced, you may
need to do some further systems and/or kernel configuration.
Hardware differences show up in a number of places:
1. CPU Architecture
If you built your image on a machine that is configured
exclusively to run, say, on Pentium 4 chipsets, and then try
to image another machine with an 80386, um ... it's not going
to work. The kernels in your image have to be compatible
with the CPU architecture on your target machine.
2. Motherboard Chipset
Motherboards have so-called "Northbridge" and "Southbridge"
chipsets. The Northbridge chip(s) control memory and high
speed graphics (like AGP). The Southbridge chip(s) control
the slower I/O functions and peripherals of the motherboard.
If the machine you're imaging uses wildly different chipsets
than the machine where the image was taken, you may have
If you have different Southbridges, you'll run into this with
any of the on-board controllers:
3. Peripheral Cards
If your newly imaged machine has different PCI and/or video
cards than the machine that produced the image, you may,
again, have to install additional or different drivers.
The good news is that FreeBSD is much more forgiving than Linux or
Windows are in this regard *so long as you can boot a GENERIC
kernel*. The whole point of the GENERIC kernel is to be able to
get the machine to boot. Once you're able to boot, it's a fairly
straightforward matter to build a custom kernel or have the boot
loader dynamically load the additional necessary kernel modules.
*Always* build your image on a machine that has a
GENERIC kernel on it even if you boot a different or
custom kernel by default. This will save your bacon
later when you are imaging to other hardware
Tim Daneliuk - email@example.com
Comments and/or improvements welcome!
This document was produced using the very useful ``reStructuredText``
tools in the ``docutils`` package. For more information, see:
This document is Copyright (c) 2008, TundraWare Inc., Des Plaines, IL
Permission is hereby given to freely distribute, copy, or otherwise
disseminate this document without charge, so long as you do so without
modifying it in any way.
``$Id: Imaging-FreeBSD-With-tbku.txt,v 1.108 2008/03/19 06:14:08 tundra Exp $``