[Bug 1335642] Re: mdadm runs into infinite loop and prevents initrd/initramfs phase to finish on boot

[Cal Leeming [Simplicity Media Ltd]]

Indeed the fix from #4 seems to solve the problem for me. I can confirm
that the update from #9 is likely right, this is certainly a race
condition, sometimes it will boot without problem and other times it
gets stuck.

If I run `ls /dev/mapper` from busybox before executing the `udevadm`
command, it doesn't show the LVM volumes. Once I run that command, the
devices then appear.

My drive configuration is as follows:

RAID 1 on 2 drives
LVM on Software RAID
Root partition on LVM, not separate boot partition
No encryption

This was an out of the box install of 14.04.3 LTS, and should almost
certainly be treated as a serious bug

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https://bugs.launchpad.net/bugs/1335642

Title:
  mdadm runs into infinite loop and prevents initrd/initramfs phase to
  finish on boot

Status in mdadm package in Ubuntu:
  Confirmed

Bug description:
  Hi all,

  probably the issue is caused by changing the SATA-port where RAID
  disks were originally attached -- this is the only thing that happened
  before my Ubuntu 14.04 (kernel-3.13.0-27) became unbootable.

  During the boot the OS runs into infinite loop reporting from time to
  time these:

  incrementally starting raid arrays
  mdadm: Create user root not found
  mdadm: create group disk not found
  incrementally started raid arrays

  Since mdadm is in initrd image, I don't even know how to skip mdadm --
  workarounds are very welcome, please!

  For example, renaming /etc/mdadm/mdadm.conf in initrd image didn't
  help, mdadm then just repeats infinitely without group/user-related
  errors:

  incrementally starting raid arrays
  incrementally started raid arrays
  incrementally starting raid arrays
  incrementally started raid arrays
  ...

  Disks are successfully assembled into a RAID under LiveCD Ubuntu 13
  (yes , i have only old CD here)

  Why I consider this a bug? because my RAID-array is needed at
  application level, not on OS-level (e.g. it is not mounted as / or
  /boot). So, if one can't boot into OS it is a serious bug. Last but
  not least, I was never choosing to put mdadm into initramfs, so it is
  a decision taken by default that leads to not-bootable system...

  UPDATE1:
  in scripts/mdadm-functions of initrd image i see this:

  mountroot_fail()
  {
      message "Incrementally starting RAID arrays..."
      if mdadm --incremental --run --scan; then
          message "Incrementally started RAID arrays."
          return 0
      else        
          if mdadm --assemble --scan --run; then
              message "Assembled and started RAID arrays."
              return 0
          else
              message "Could not start RAID arrays in degraded mode."
          fi
      fi
      return 1
  }

  i tried 'mdadm --incremental --run --scan -c <path to
  etc/dmadm/dmadm.conf of initrd image> -v' and it exits silently
  without creating /dev/md/127 as I have expected.

  Whereas

  sudo mdadm --assemble --run --scan -c ./etc/mdadm/mdadm.conf -v

  Does the job. Is it an issue just of incremental mode?

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