[Bug 1652761] Re: [16.04 LTS] systemd systemd-remount-fs does NOT remount root writeable but says it did

[h]

I found out my /etc/fstab has been empty so systemd-remount-fs falsely
thought it had nothing to do.

This is still a bug, as Ubuntu crashes at bootup without any further
notice.

A)  systemd-remount-fs MUST NOT sys OK if / and /usr aren't writeable after finishing it's job
B)  Ubuntu's starting MUST NOT believe in systemd-remount-fs and especially it is NOT allowed to fail silently if something it expects isn't the case

One of those has to implement a fallback of simply issuing a "mount -o
remount,rw" for /, /usr and /home -- or at least ask the user if it
should do so and/or start the recovery menu.

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Title:
  [16.04 LTS] systemd systemd-remount-fs does NOT remount root writeable
  but says it did

Status in systemd package in Ubuntu:
  New

Bug description:
  On boot root does not get remounted rewriteable and leads to system
  freezing.

  Symptoms:
  - Regular boot stops after unpacking initramfs

  
  Steps to reprocude (on my system):
  1. Boot into recovery, which still works
  2. Select "repair dpkg", then select remount root writeable
  Systemd now says it remounted root writeable, a green "[OK]"
  Followed complains of dpkg  beacause root's not writeable
  3. select "root shell" in the recovery menu
  4. there proof that / not mountable with "touch /tmp/x"
  5. execute fsck and see, everythings ok
  6. execute "mount -o remount,rw /"
  7. see that root is now writeable with "touch /tmp/x"
  8. close root shell and choose to continue boot in recovery menu
  9. system is starting now without any problems

  Two things go wrong here:
  A) root isn't remounted writeable but there's no reason to refuse 
  B) systemd says OK, but didn't do it job

  
  Various Information about installed Ubuntu:
  $ uname -a
  Linux Z30 4.4.0-21-generic #37-Ubuntu SMP Mon Apr 18 18:33:37 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
  $ cat /etc/issue
  Ubuntu 16.04.1 LTS \n \l

  $ dpkg -S /lib/systemd/systemd-remount-fs
  systemd: /lib/systemd/systemd-remount-fs
  $ dpkg -l systemd | grep ^ii
  ii  systemd        229-4ubuntu13 amd64        system and service manager

  I tried this with various kernels without any difference in behaviour
  (4.4.0-21, 4.4.0-31, 4.4.0-53, 4.4.0-47).

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