update-initramfs fails when cp encounters empty directory

[Haravikk]

I recently upgraded to UbuntuServer 16.04 but encountered the following problem:

    dpkg --configure linux-image-4.4.0-45-generic
    Setting up linux-image-4.4.0-45-generic (4.4.0-45.66) ...
    Running depmod.
    update-initramfs: deferring update (hook will be called later)
    The link /initrd.img is a dangling linkto /boot/initrd.img-4.4.0-45-generic
    vmlinuz(/boot/vmlinuz-4.4.0-45-generic
    ) points to /boot/vmlinuz-4.4.0-45-generic
     (/boot/vmlinuz-4.4.0-45-generic) -- doing nothing at /var/lib/dpkg/info/linux-image-4.4.0-45-generic.postinst line 491.
    Examining /etc/kernel/postinst.d.
    run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 4.4.0-45-generic /boot/vmlinuz-4.4.0-45-generic
    run-parts: executing /etc/kernel/postinst.d/initramfs-tools 4.4.0-45-generic /boot/vmlinuz-4.4.0-45-generic
    update-initramfs: Generating /boot/initrd.img-4.4.0-45-generic
    cp: omitting directory '/etc/udev/rules.d/70-persistent-net.rules'
    E: /usr/share/initramfs-tools/hooks/udev failed with return 1.
    update-initramfs: failed for /boot/initrd.img-4.4.0-45-generic with 1.
    run-parts: /etc/kernel/postinst.d/initramfs-tools exited with return code 1
    Failed to process /etc/kernel/postinst.d at /var/lib/dpkg/info/linux-image-4.4.0-45-generic.postinst line 1052.
    dpkg: error processing package linux-image-4.4.0-45-generic (--configure):
     subprocess installed post-installation script returned error exit status 2
    Errors were encountered while processing:
     linux-image-4.4.0-45-generic

With a bit of digging I determined the issue was with this line (after initially disregarding it):

    cp: omitting directory '/etc/udev/rules.d/70-persistent-net.rules'

The path specified turned out to be an empty directory, hence why cp omitted it, so I simply deleted it and tried again, this time successfully.

It seems that update-initramfs, or some other component of it, is treating a cp omission as a failure and erroring out, rather than continuing, while looking into the problem I found a few variations of the problem (directories other than udev) so it seems like this behaviour could do with being changed to prevent this issue in future.

Version information:
    lsb_release -rd
    Description: Ubuntu 16.04.1 LTS
    Release: 16.04

    initramfs-tools:
      Installed: 0.122ubuntu8.5
      Candidate: 0.122ubuntu8.5
      Version table:
     *** 0.122ubuntu8.5 500
            500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
            500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main i386 Packages
            100 /var/lib/dpkg/status
         0.122ubuntu8 500
            500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
            500 http://us.archive.ubuntu.com/ubuntu xenial/main i386 Packages

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.