[Bug 1489855] Re: Change to mount sequence order breaks persistence on casper-rw partitions

Sat Apr 4 02:07:42 UTC 2020

After some additional tests, it seems I was a bit too hasty to declare
that there exists a regression, as, even though a similar error is
displayed as the one from the original bug, the persistent partition
appears to be mounted regardless.

For the record however, `/var/log/boot.log` displays the following error
while mounting the persistent partition:

--------------------------------------------------------
ln: /tmp/mountroot-fail-hooks.d//scripts/init-premount/lvm2: No such file or directory
mount: mounting /cow on /root/cow failed: No such file or directory
adduser: The user `ubuntu' already exists.
[FAILED] Failed unmounting /cdrom.
--------------------------------------------------------

Also, the introduction of `/casper/vmlinuz$casper_flavour` in `grub.cfg`
does add a new hurdle to utilities, such as Rufus, that attempt to add
the required 'persistent' keyword to the kernel options, because, of
course, the new `$casper_flavour` variable makes it even more difficult
to insert the keyword in a location that is not going to cause trouble.

I sure wish persistence on Linux didn't require developers of boot
utilities to treat every single release as its own special case, and/or
end up to the boot process to throwing error messages that seem to
indicate that there exists and issue.

As such, I would strongly encourage to test at least UEFI boot in the following manner:
- One FAT32 partition where the whole content of the Ubuntu ISO has been extracted (and grub.cfg patched to enabled persistence)
- One ext3 or ext4 casper-rw partition following the FAT32 partition (since this has been the longtime recommended way of enabling persistence for Ubuntu)

The above is a a very reasonable way to expect persistence to be
achieved for 20.04 LTS, so if it does throw errors, as it currently
appears to do, I would assert that there are still some improvements
that could be made.

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https://bugs.launchpad.net/bugs/1489855

Title:
  Change to mount sequence order breaks persistence on casper-rw
  partitions

Status in casper package in Ubuntu:
  Fix Released

Bug description:
  the system boots fine when using a casper-rw FILE but drops to a
  busybox when using a partition

  the short log would be:
  ___________________________________________________
  Begin: Running /scripts/casper-premount ... done.
  done.
  umount: can't umount /cdrom: Device or resource busy
  Warning: Unable to find the persistent home medium
  umount: can't umount /cdrom: Device or resource busy
  Warning: Impossible to include the casper-sn Snapshot
  umount: can't umount /cdrom: Device or resource busy
  Warning: Impossible to include the home-sn Snapshot
  done.
  ___________________________________________________

  removing the "persistence" keyword from the syslinux.cfg works and the live usb drive boots just fine.
  using a persistence file instead of the partition and the usb drive boots just fine.

  i found older bug reports concerning the same problem but the fix
  proposed in 2010 is already integrated into the script "casper".

  so i started the flashdrive with the casper debug= option and i see
  the following (after probing several other devices it finally finds
  the right device and partition (sdb3)

  ___________________________________________________

  + cow_backing_mp=/cdrom
  + [ -e /cdrom/casper-rw ]
  + umount /cdrom
  + sys2dev /sys/block/sdb/sdb3
  + sysdev=/block/sdb/sdb3
  + udevadm info -q name -p /block/sdb/sdb3
  + echo /dev/sdb3
  + devname=/dev/sdb3
  + /sbin/blkid -s LABEL -o value /dev/sdb3
  + [ casper-rw = casper-rw ]
  + echo /dev/sdb3
  + return
  + cowprobe=/dev/sdb3
  + [ -b /dev/sdb3 ]
  + cowdevice=/dev/sdb3
  + get_fstype /dev/sdb3
  + local FSTYPE
  + local FSSIZE
  + fstype
  + eval FSTYPE=ext4 FSSIZE=8458862592
  + FSTYPE=ext4 FSSIZE=8458862592
  + [ ext4 != unknown ]
  + echo ext4
  + return 0
  + cow_fstype=ext4
  + cow_mountopt=rw,noatime
  + mount -t ext4 -o rw,noatime /dev/sdb3 /cow
  + [ ! -d /cow/upper ]
  + mkdir -p /cow/upper
  + continue
  + continue
  + mkdir -p /cow/work
  + [ -f /cow/format ]
  + [ DEFAULT = DEFAULT ]
  + modprobe -q -b overlay
  + grep -q ^overlay$
  + cut -f2 /proc/filesystems
  + UNIONFS=overlay
  + break
  ___________________________________________________

  this looks fine to me.. it looks like it recognizes everything .. it's
  ext4 .. label casper-rw.. it's mounting it...

  a little bit further down in the loooong log file it states the
  following:

  ______________________________________________

  + cow_backing_mp=/home-rw-backing
  + [ -e /home-rw-backing/home-rw ]
  + umount /home-rw-backing
  + sys2dev /sys/block/sdb/sdb3
  + sysdev=/block/sdb/sdb3
  + udevadm info -q name -p /block/sdb/sdb3
  + echo /dev/sdb3
  + devname=/dev/sdb3
  + /sbin/blkid -s LABEL -o value /dev/sdb3
  + [ casper-rw = home-rw ]
  + get_fstype /dev/sdb3
  + local FSTYPE
  + local FSSIZE
  + fstype
  + eval FSTYPE=ext4 FSSIZE=8458862592
  + FSTYPE=ext4 FSSIZE=8458862592
  + [ ext4 != unknown ]
  + echo ext4
  + return 0
  + [ ext4 = vfat ]
  + homecow=
  + [ -b ]
  + [ n != y ]
  + log_warning_msg Unable to find the persistent home medium
  + _log_msg Warning: Unable to find the persistent home medium\n
  + [ n = y ]
  + printf Warning: Unable to find the persistent home medium\n
  Warning: Unable to find the persistent home medium
  __________________________________________________________

  a warning about the home medium is shown in both cases (file and partition) but the persistence file works never the less..

  my system:  

  kubuntu linux 15.10 beta1

  uname -a
  Linux wald 4.1.0-3-generic #3-Ubuntu SMP Tue Jul 28 12:25:10 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

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