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

[Warren Togami]

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?

Warren Togami
wtogami at redhat.com