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

[EvilSupahFly]

On ext4, the journal is written to the same location over and over
again, which can have a seriously negative impact on the lifespan of the
flash memory. If you want your USB stick to last longer, consider using
ext2 instead because it doesn't use journaling. Otherwise, well done
Pankaj!

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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:
  Confirmed

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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