update-initramfs hangs during mdadm hook

[Scott Moser]

$ sudo update-initramfs -v -c -t -k 4.4.0-34-generic

...
Adding binary /sbin/mdadm
Adding binary /sbin/mdmon
W: mdadm: /etc/mdadm/mdadm.conf defines no arrays.

<hang>

I can't install a kernel as a result.
the issue seems to be hanging of
 /sbin/mdadm --examine --scan --config=partitions
during
  /usr/share/initramfs-tools/hooks/mdadm
which calls
 /usr/share/mdadm/mkconf

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: mdadm 3.3-2ubuntu7.1
ProcVersionSignature: User Name 4.4.0-31.50-generic 4.4.13
Uname: Linux 4.4.0-31-generic ppc64le
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: ppc64el
Date: Wed Aug 24 21:08:10 2016
Lsusb:
 Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
 Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
 Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MDadmExamine.dev.sda: Error: command ['/sbin/mdadm', '-E', '/dev/sda'] failed with exit code 1: mdadm: cannot open /dev/sda: Permission denied
MDadmExamine.dev.sda1: Error: command ['/sbin/mdadm', '-E', '/dev/sda1'] failed with exit code 1: mdadm: cannot open /dev/sda1: Permission denied
MDadmExamine.dev.sda2: Error: command ['/sbin/mdadm', '-E', '/dev/sda2'] failed with exit code 1: mdadm: cannot open /dev/sda2: Permission denied
MDadmExamine.dev.sdb: Error: command ['/sbin/mdadm', '-E', '/dev/sdb'] failed with exit code 1: mdadm: cannot open /dev/sdb: Permission denied
MDadmExamine.dev.sdc: Error: command ['/sbin/mdadm', '-E', '/dev/sdc'] failed with exit code 1: mdadm: cannot open /dev/sdc: Permission denied
MDadmExamine.dev.sdd: Error: command ['/sbin/mdadm', '-E', '/dev/sdd'] failed with exit code 1: mdadm: cannot open /dev/sdd: Permission denied
MDadmExamine.dev.sde: Error: command ['/sbin/mdadm', '-E', '/dev/sde'] failed with exit code 1: mdadm: cannot open /dev/sde: Permission denied
MDadmExamine.dev.sdf: Error: command ['/sbin/mdadm', '-E', '/dev/sdf'] failed with exit code 1: mdadm: cannot open /dev/sdf: Permission denied
MDadmExamine.dev.sdg: Error: command ['/sbin/mdadm', '-E', '/dev/sdg'] failed with exit code 1: mdadm: cannot open /dev/sdg: Permission denied
MDadmExamine.dev.sdg1: Error: command ['/sbin/mdadm', '-E', '/dev/sdg1'] failed with exit code 1: mdadm: cannot open /dev/sdg1: Permission denied
MDadmExamine.dev.sdg2: Error: command ['/sbin/mdadm', '-E', '/dev/sdg2'] failed with exit code 1: mdadm: cannot open /dev/sdg2: Permission denied
MDadmExamine.dev.sdh: Error: command ['/sbin/mdadm', '-E', '/dev/sdh'] failed with exit code 1: mdadm: cannot open /dev/sdh: Permission denied
MDadmExamine.dev.sdi: Error: command ['/sbin/mdadm', '-E', '/dev/sdi'] failed with exit code 1: mdadm: cannot open /dev/sdi: Permission denied
MDadmExamine.dev.sdj: Error: command ['/sbin/mdadm', '-E', '/dev/sdj'] failed with exit code 1: mdadm: cannot open /dev/sdj: Permission denied
MDadmExamine.dev.sdk: Error: command ['/sbin/mdadm', '-E', '/dev/sdk'] failed with exit code 1: mdadm: cannot open /dev/sdk: Permission denied
MDadmExamine.dev.sdl: Error: command ['/sbin/mdadm', '-E', '/dev/sdl'] failed with exit code 1: mdadm: cannot open /dev/sdl: Permission denied
ProcEnviron:
 TERM=screen.xterm-256color
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: root=/dev/mapper/mpath0-part2 ro console=hvc0
ProcLoadAvg: 0.51 0.88 0.96 1/1428 73716
ProcMDstat:
 Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
 unused devices: <none>
ProcSwaps:
 Filename Type Size Used Priority
 /swap.img file 8388544 0 -1
ProcVersion: Linux version 4.4.0-31-generic (buildd@bos01-ppc64el-028) (gcc version 5.3.1 20160413 (User Name/IBM 5.3.1-14ubuntu2.1) ) #50-User Name SMP Wed Jul 13 00:05:18 UTC 2016
SourcePackage: mdadm
UpgradeStatus: No upgrade log present (probably fresh install)
cpu_cores: Number of cores present = 20
cpu_coreson: Number of cores online = 20
cpu_smt: SMT is off
etc.blkid.tab: Error: [Errno 2] No such file or directory: '/etc/blkid.tab'

[Kai Mast (kai-mast)]

Can confirm this on multiple machines. Removing the mdadm package fixes it but some folks might need that...

There's a bunch of other people seeming to have this problem too: https://askubuntu.com/questions/1255546/update-initramfs-stuck/1256262