[Bug 1543204] Re: cloud images should have /lib/modules inside

[Scott Moser]

Just for later reference, similar bug 1792905.

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https://bugs.launchpad.net/bugs/1543204

Title:
  cloud images should have /lib/modules inside

Status in maas-images:
  Fix Released
Status in livecd-rootfs package in Ubuntu:
  New

Bug description:
  maas images for xenial recently removed the kernel being installed inside.
  Now, usage of modules after the initramfs depends upon cloud-initramfs-copymods being able to copy (tmpfs bind mount) the /lib/modules/VERSION from the initramfs into the root.

  cloud-initramfs-copymods does this by just bind-mounting a directory with VERSION over the top of lib/modules in the rootfs.
  If that directory is not present, then it cannot perform that mount.

  
  The fix then would be either:
  a.) ensure that all ubuntu images have /lib/modules inside them
      Currently the lxd images do not have /lib/modules in them.
  b.) cloud-initramfs-copymods learn how to address this issue.
      Its very non-trivial to do this, as cloud-initramfs-copymods executes when the target root is mounted read-only.  In order to solve the problem then, the initramfs would have to put its copy somewhere else and rely on a process moving the mount after / is mounted rw.  And then, there is a possibility that / is *never*  mounted RW.
  c.) fix maas images build process  to insist that its output contains /lib/modules
      currently the build process uses the cloud-image and then removes a kernel (which probably gets /lib/modules removed).  The end goal is to use lxd images directly (at very least from a filesystem-contents perspective) so we'd' like to have the fix in 'a'.

  I'll fix 'c' which will unbreak us for now.
  I'll ask cloud images team to ensure /lib/modules is present.

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