Bug#877776: live-boot: fixed read-only mode with overlayfs
Hi all
> Can you be a bit more verbose in your explanation?
OK, I try:
live-boot in Debian 9 uses overlayfs per default instead of aufs in
Debian 8. One difference between aufs and overlayfs is that aufs can
operate directly on the file system root but overlayfs needs certain
subdirectories (rw and work) on the file system root. Here is a quote
from https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt:
--------------------
The "workdir" needs to be an empty directory on the same filesystem as
upperdir.
--------------------
This fact was partly taken care of in live-boot in the script
9990-misc-helpers.sh, see here:
https://anonscm.debian.org/cgit/debian-live/live-boot.git/tree/components/9990-misc-helpers.sh#n1335
The important part here is the postfix "/rw" in the option
"upperdir=${unionrw}/rw"
Unfortunately, these subtleties of overlayfs were not taken into account
when using it as a lower layer (when you add the boot option
"persistence-read-only"). This is what my patch fixes.
> How can we reproduce the problem?
Create a Debian Live system with a persistence partition, use it first
in normal "read-write" mode and change some files and settings. Then
reboot and use the boot option "persistence-read-only". You will see
that non of your previous changes are visible because the persistence
partition got mounted the wrong way (without the "/rw" postfix).
> Why is your patch fixing the issue?
Because it correctly mounts the persistence partition in the overlayfs
case including the necessary "/rw" postfix.
Cheers
Ronny
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