Re: LiveCD wiping root partition?

Douglas McClendon <dmc.fedora@xxxxxxxxxxxxxxxxxxxxxx> · Tue, 31 Jul 2007 12:23:00 -0500

Douglas McClendon wrote:
Michel Salim wrote:
I just did a clean install of Fedora 7 from the live CD onto my laptop,
which previously had a Fedora install upgraded from one of the F7 test
releases, partitioned as suggested by anaconda (LVM, one swap partition,
everything else under '/')

When reinstalling, I kept the partition layout and specifically told
Anaconda *not* to reformat / (having booted in rescue mode beforehand, 
and
removing everything but /home). Anaconda gave a warning that the leftover
files might interfere with the installed system, which gave the 
impression
that those files won't actually be removed during installation.

I don't remember the specific warning, but if it is not clearly 
indicating that unselecting the format option on '/' is not allowed, 
then that is a bug that should be fixed either with better user 
messages, or alternate installation mechanisms.

WOW.  I was wrong.  There is NO such message.  That is a horrible bug.  I may 
try to check to see if it's still in the latest anaconda, and provide some sort 
of simple patch later today.

Also, to answer your question more thoroughly than my first reply-  Yes, after 
the dd, if there is a seperate /usr or other partitions, files are then copied 
from / to there.  This is all very related to my turboLiveInst patch which I 
recently posted to livecd-list and anaconda-devel.

I'm surprised I don't remember hearing about this bug before.  I had personally 
run into the same warning you saw, but that is just a general warning that has 
nothing to do with the livecd installer case specifically, and the livecd 
installer will stupidly let you just march along with the / fs not scheduled for 
formatting, even though it is going to anyway.

-dmc

I didn't have anything to do with what's in F7, though I did know enough 
about it to catch the fact that the 'formatting / filesystem' during the 
process was meaningless and time consuming, so that will be gone from 
from F8.

As it turns out, however, the old contents are completely gone (I'm 
trying
out different recovery tools now to see if I could rescue some of the 
data).
It's as if the live CD simply used dd to transfer the install image to 
the
hard drive (in which case, how does it actually handle different 
partition
layouts, e.g. /usr, /var, /home on separate partitions -- does it just 
move
the files afterwards?)

As it stands it seems that the Live CD is a very dangerous tool, at 
least as
long as
1) the default behaviour of Anaconda is to put everything under /
2) it does not carry more warnings about what it will do to the / 
partition
during installation

Could someone let us know how the live CD actually performs its work? 

It takes a 4.0G ext3 fsimage from the cd, effectively dd's it to the 
chosen root volume, then does a resize2fs.

It
would aid tremendously in the data recovery part. Would 'dd'-ing the 
entire
partition to an external drive, and mounting it on a Windows computer 
(most
recovery tools are unfortunately for that platform) preserve all the data
required? I'm assuming that the new installation overwrote the same 
parts of
the disk that was used to hold the OS in the previous install.

As long as you haven't done much, data that was sitting in the first 
4.0G of the filesystem will be gone, but data in the rest should be 
largely untouched.  I have no idea how to go about trying to recover it 
(haven't used any windows tools), except asking for expensive 
professional date recovery help.  Or if all I cared about was a text 
file, using 'strings' and 'grep' on chunks of the disk data.

-dmc