Re: Return a Debian system to a pristine state
Hi,
Michael Howard wrote:
> With linux (debian) you could just create an image (using dd for example) of
> the drive in order to restore it at a later date.
If a backup shall have a chance to be absolutely safe it must be done
while the backuped filesystems are unmounted or mounted read-only.
This implies that it must be done by an operating system that it not
using these to-be-backuped filesystems for its own needs. Debian Live
comes to my mind.
The risk of backing up a write enabled filesystem is in the time span of
the backup procedure. Around this time, the consistency of files like
data bases is endangered by copying one file or file part while it is in
an older state and later a file or file part which is already in a newer
state.
With data bases there is usually a software specific procedure to get a
consistent snapshot without shutting them down. But in general there are
too many things which could go wrong in this aspect.
Filesystem snapshots reduce the risk but cannot completely avoid it,
because the filesystem is not aware of all semantic interconnections
between file content. They help by making the time window for such mishaps
smaller. But only one of a group of consistency-sensitive write operations
has to lie on the other side of the snapshot time to create a chance for
inconsistency.
The problem is not that important if you make frequent backups for recovery
of small and big disasters while taking special care of data bases. The
resulting backups are still better than nothing and potential inconsistencies
can in most cases be resolved by using files from the next older backup.
> However, with debian, if you want to revert to a pristine state, what is
> easier or quicker than doing a re-install?
Do we have a feature to get a list of installed packages and to later
use it for re-installation ?
I normally need weeks to get everything installed on my next machine.
In the beginning it is easy to choose the big chunks. But the previous
machine is then old as stone and can hardly serve for the fine tuning.
So i need to find out what's still missing and install on demand.
Have a nice day :)
Thomas
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