diff --git a/Imaging-FreeBSD-With-tbku.txt b/Imaging-FreeBSD-With-tbku.txt index a706e62..b73819a 100644 --- a/Imaging-FreeBSD-With-tbku.txt +++ b/Imaging-FreeBSD-With-tbku.txt @@ -1 +1,419 @@ -$Id: Imaging-FreeBSD-With-tbku.txt,v 1.101 2008/03/11 17:25:34 tundra Exp $ +How To Image FreeBSD Systems Using ``tbku`` +============================================== + +This document describes how to use the TundraWare Inc. ``tbku`` +utility to "image" or "clone" FreeBSD systems. + + .. Warning:: + + 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 + drive. + + + + +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 +possible. + +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 +on. + +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 (unless you already have an ``AutoYAST`` configuration ready to +go). It may be simpler to image the target machine with your web +server image, boot it, reconfigure it as a database server, and then +take the image. + + +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 +first place. + +If you've never used it before, take a moment to download it and read +the documentation. You'll find the latest copy at: + + http://www.tundraware.com/Software/tbku + +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 +tarball. + + .. Note:: + + 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. + + .. Note:: + + 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`_ + section. + + + 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 + fileset:: + + /bin + /boot + /dwnl + /etc + /home + /lib + /local + /opt + /root + /sbin + /srv + /usr + /var + + 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``. + + 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. + + Provisioning Machines With A Master Image + + 1. Boot the FreeBSD installation disk and load the + ``Rescue System``. + + 2. Now we have to prepare the disk to receive a FreeBSD + filesystem. The example below assumes we are installing on + ``/dev/hda`` - a PATA master on the first IDE controller - + but that the image came from a system that boots from the + first SCSI drive, ``/dev/sda``. Keep in mind you can do + what follows with any of the drives on your system. Just + substitute the device names as appropriate:: + + +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 +explanation. + +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 +it! + +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. + + +Gotchas +======= + + +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. + +There is no general way to solve these sorts of problems. You'll have +to dig through ``YAST`` (if the system boots at all) and/or the individual +configuration tools to correct things. + + .. Note:: + + Imaging is not the answer to every new installation + problem. At some point, it becomes simpler to + do a fresh install of FreeBSD than to try + and "tweak" an existing image to get it running + properly. + + +As a personal preference, I like to work directly with configuration +files from the command line whenever I can. If the target machine +will not boot, you sort of have no other choice. You'll have to do +something like this to get to those files to edit them. Boot the +installation CD and select ``Rescue System``, then mount the target +drive(s):: + + mount /dev/hda2 /mnt + +You can then edit the files found under ``/mnt``. + + +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 encounter: + + + 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 all easily done via ``YAST`` or by editing the relevant + configuration files directly. 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. + + 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. + + However "booting" and "running properly" are two different + things. In the process of preparing this documentation, I + discovered that my newly imaged test machine *refused* to set + the PATA drive into UDMA modes 5/6. Why? Because the machine + used to create the original image had an older (different) + chipset than the newly imaged machine. I had to figure out + which additional drivers the kernel needed to load for it + to work properly on the new hardware. + + 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 Xeon chipsets, and then try + to image another machine with a Pentium 4, 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're going to probably have + problems. + + This was the case in the example above. By default, SUSE + Linux could boot IDE in its slowest possible mode, but + it could not exploit the higher speed UDMA features + of the new Southbridge chipset - that required the + installation of a driver specific for that chipset. + + If you have different Southbridges, you'll run into this + with any of the on-board controllers: + + - Audio + - Buses + - Disk + - Joystick + - Network + - Video + + 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. + + +Configuring Drivers +------------------- + +Let's assume you can boot your machine fine, but you need to get +additional or different drivers to load for the machine to run +optimally. The kernel configuration is in this file:: + + /etc/sysconfig/kernel + +In that file, you'll see a line something like this:: + + INITRD_MODULES="piix aic7xxx processor thermal fan reiserfs edd" + +Now, suppose we want to add the drivers for, say, a VIA chipset. +We'd edit that line as follows:: + + INITRD_MODULES="piix aic7xxx sata_via via82cxxx processor thermal fan reiserfs edd" + +Then we have to create a new ``initrd`` like this:: + + mkinitrd + +Now unmount the drive and reboot. + + .. Note:: + + If you *cannot* boot your new system, boot the + installation CD as before and get into the ``Rescue + System``. Mount the target drive under ``/mnt`` as we + did previously. This will allow you to edit + ``/mnt/etc/sysconfig/kernel`` as needed. You can then + run ``mkinitrd`` with options to write the updated file + onto your target drive. See ``man mkinitrd`` for the + details. + + + +The trick here is know *which* drivers you'll need. That's going +to take some digging on your part. Generally, you'll find +the compiled driver modules under:: + + /lib/modules/<kernel-name>/kernel + +But, it's going to be up to you to figure out which of these your +particular hardware actually needs. + +In the end, unless the differences in source and target hardware are +fairly small/simple, you're typically better off to do a new +installation for each class of hardware you run, and create separate +image for each of them. + + +Author +====== + + Tim Daneliuk - tbku@tundraware.com + + Comments and/or improvements welcome! + + +Document Information +==================== + +This document was produced using the very useful ``reStructuredText`` +tools in the ``docutils`` package. For more information, see: + + http://docutils.sourceforge.net/rst.html + +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 1.102 2008/03/13 23:10:59 tundra Exp $