[Fedora-livecd-list] The long-awaited landing of persistence

Jeremy Katz katzj at redhat.com
Thu Mar 6 20:38:32 UTC 2008


On Thu, 2008-03-06 at 15:20 -0500, Warren Togami wrote:
> Jeremy Katz wrote:
> > The quick steps of how to take advantage of the functionality:
> > 1) Build a live image using the newer mkinitrd (6.0.32) in your repos
> > 2) Use the updated livecd-iso-to-disk.sh with an --overlay-size-mb=512
> > (or 1024 or whatever based on the capacity of your USB stick minus the
> > size of the ISO)
> 
> if [ -n "$overlaysizemb" ]; then
>      echo "Initializing persistent overlay file"
>      OVERFILE="overlay-$( /lib/udev/vol_id -l $USBDEV )-$(
> /lib/udev/vol_id -u $USBDEV )"
>      dd if=/dev/null of=$USBMNT/LiveOS/$OVERFILE \
>          count=1 bs=1M seek=$overlaysizemb
> 
> Warning!
> 
> If your USB stick is vfat filesystem and $overlaysizemb is
> some number larger than your RAM, your system will swap storm and die.
> According to Ulrich Drepper this isn't dd using all RAM, but it is up to
> the filesystem implementation.  Since the OOM happens in kernel space it
> cannot OOM kill anything and recover.
> 
> I just tried the same thing with the USB stick reformatted as ext3.  It 
> successfully created the sparse file without any problem.
> 
> Perhaps this means we cannot support overlay images on vfat?

Or we may need to limit the size that we support.  Warren and I are
looking a little closer now...

Jeremy




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