Once you have backups, you can and should test the ability to restore those backups to a new hardware environment. The restore procedure is going to depend on what you used to create your "image" in the first place. Independent of the notion of backups, a system administrator (or even an experienced user) will want to "clone" a computer system. That is make an identical copy or nearly identical copy of a computer on different hardware. The most widespread use-case for this is when a person gets a new computer and wants to migrate the old computer software and data to the new hardware. From the system administrator's perspective, the common use case is different: it's when you have to build out a cluster, provide redundancy, or otherwise scale a hardware/software platform.
Consider all the times that you could produce a system that you wish to replicate. For example, a standard "Developer's Workstation" or "Designer's Studio" or "Student Desktop" and many more technical varieties like "Web Front-end", "Mail Relay" etc.
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Apt-get --set-selections
One way to do this on Debian-based systems (including Ubuntu) is to use dpkg get/set-selections in combination with apt-get using it's dselect-upgrade option:
To clone the package installation state of System A to System B do the following:
on System A
sudo dpkg --get-selections > package-list.txt
copy package-list.txt from System A to System B
on System B
sudo dpkg --set-selections < package-list.txt
sudo apt-get -u dselect-upgrade
You might get 'database' errors, in which case you should install dselect and update that as well (all as root, or with sudo):
apt-get update
apt-get install dselect
dselect update
apt-get -u dselect-upgrade
There are other tools to do the job too, and the tools you want to use for this depend on how automated you aim for this task to be, and how much you need/want to be able to customize each machine as it's being installed.
KickStart
Kickstart is a Red Hat package that deploys Red Hat to multiple installation targets with minimal customisation. Aside from the wiki, it is also covered in the Installation Guide for RedHat Enterprise Linux
System Imager
SystemImager is a third-party tool that does a better job. http://systemimager.org/
Fully Automated Install
fai (fully automated install) is a Debian-based tool to do likewise. Like System Imager, it's suitable for building clusters. See the
Replicator
Replicator seems like it could use some volunteers to expand. http://replicator.sourceforge.net/ It tries to do some customization for differences in hard disk sizes, video cards, etc. You may want to check it out.
Partition Image
Partition Image is a semi-automated tool for replicating a Linux partition to multiple targets. It is particularly useful as a system cloning tool, and has many uses for data backup and archiving of whole disks or partitions.