[Bug 1877078] Re: Please ship empty /etc/fstab in LXD images

[Steve Langasek]

On Tue, Aug 25, 2020 at 02:20:50PM -0000, Balint Reczey wrote:
> @vorlon What is your plan regarding this fix? The revert may have helped
> MAAS, but broke all LXD instances. IMO if MAAS relied on having a broken
> fstab then MAAS should be fixed and not LXD images should be broken, so
> I'd prefer having this fix in again. Maybe with /etc/fstab as an empty
> file which is not particularly beautiful, but not invalid at least.

MAAS images were broken because cloud-init could not handle the new
behavior.  This is not the MAAS team's responsibility to fix, the Server
Team has been working on it with Dimitri; and having our MAAS images broken
was an unacceptable regression that was blocking kernel testing.

See the other linked bug, LP: #1890803, for details.  If the
cloud-initramfs-tools change has landed, then the livecd-rootfs revert can
be reverted again.

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https://bugs.launchpad.net/bugs/1877078

Title:
  Please ship empty /etc/fstab in LXD images

Status in livecd-rootfs package in Ubuntu:
  Triaged
Status in systemd package in Ubuntu:
  Triaged

Bug description:
  Systemd boots degraded because of the invalid content of /etc/fstab:

  $ lxc shell gg-test 
  root at gg-test:~# systemctl is-system-running 
  degraded
  root at gg-test:~# systemctl list-units --failed 
    UNIT                       LOAD   ACTIVE SUB    DESCRIPTION                         
  ● systemd-remount-fs.service loaded failed failed Remount Root and Kernel File Systems

  LOAD   = Reflects whether the unit definition was properly loaded.
  ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
  SUB    = The low-level unit activation state, values depend on unit type.

  1 loaded units listed.
  root at gg-test:~# cat /etc/fstab 
  LABEL=cloudimg-rootfs	/	 ext4	defaults	0 0
  root at gg-test:~# echo "" > /etc/fstab 
  root at gg-test:~# reboot

  Session terminated, killing shell... ...killed.
  rbalint at yogi:~$ lxc shell gg-test 
  root at gg-test:~# systemctl is-system-running 
  running
  root at gg-test:~# systemctl list-units --failed 
    UNIT LOAD ACTIVE SUB DESCRIPTION
  0 loaded units listed.

  
  Not shipping is also fixing the issue, but some programs (such as systemd autopkgtes) reads fstab and a missing fstab should be special-cased, thus that would cause more breakages.

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