On Monday 07 August 2006 06:50, Richard Andrews wrote:
> I'm looking for advice on building up a filesystem image file.
>
> I have a working server that I want to mimick in UML. What is the best way
> to get the filesystem of the real server into a UML filesystem image? What
> are the gotchas? eg. I can immediately suspect device configs and partition
> tables would be problematic.

To work on:

/etc/fstab
/etc/inittab maybe

Device configs:
things like hwclock, consolefonts and X11 don't make sense in UML (however you 
can run Xnest instead of normal X by changing a symlink somewhere). In some 
distros (e.g. Debian) the initscripts recognize UML and skip calling those 
tools.

Partition tables: you'd normally copy a single partition rather than a disk, 
so you don't get partition tables.

The reason for this is that when you have a partition table on a file, 
mount -o loop does not parse the table, so you need a script (easily 
writable) to calculate the offset and pass it as offset=$n_sectors to mount 
or losetup. And this is not widely known.

> My understanding is that the filesystem image is just the result of a
> "mount -o loop" situation. Is this true or are there additional elements to
> the filesystem image file?

Yes, that's correct.

> Eventually I'm also interested in going the other way too: tuning the UML
> system config then putting those changes back onto the real servers. What
> do should I keep in mind when creating the UML image that will help me
> avoid problems going back to the real servers?

Never tried that, however I could say "make a patch for your Uml-related 
changes to /etc/fstab and similar material". If /dev/hdaN / /dev/ubda is used 
elsewhere, you'll probably want to setup some symlinks in 

> Thanks
>
> --
>   Rich

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
Chiacchiera con i tuoi amici in tempo reale! 
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