Comment 5 for bug 1337538

The failure you're showing above is from 'chroot $TARGET update-initramfs -u'.

Curtin does this in curthooks because curtin/commands/curthooks.py:
    # As a rule, ARMv7 systems don't use grub. This may change some
    # day, but for now, assume no. They do require the initramfs
    # to be updated, and this also triggers boot loader setup via
    # flash-kernel.
    machine = platform.machine()
    if machine.startswith('armv7'):
        update_initramfs(target)
    else:
        setup_grub(cfg, target)

There are a few things I'm not sure of:
 a.) why 'mkimage' isnt available inside your target.
   If the target was created from the ephemeral image (which is the normal process) then it would be, as we've demonstrated above that the ephemeral image has 'mkimage'.
 b.) if curtin *should* call 'update_initramfs' in the target on this system.
 c.) if mkimage is a requirement of update-initramfs, then why is it not a dependency of initramfs-tools.
      I'm admittedly not fully aware of the relationship of initramfs-tools and mkimage, but personally the above seems like a bug in update-initramfs or its packaging.