Comment 3 for bug 1827157

Note that the kernel version used in the original 18.04.1 ISO (ubuntu-18.04.1-desktop-amd64.iso) is:

    4.15.0-29

When this ISO is exacted, the the boot directory does not contain a vmlinuz or initrd file.

This means, when `ap upgrade` is executed thes three new boot files are added to the system:
    boot/initrd.img-4.18.0-15-generic
    boot/initrd.img-4.18.0-18-generic
    boot/vmlinuz-4.18.0-18-generic

However, the following vmlinux file is not added:
    boot/vmlinuz-4.18.0-15-generic

As an additional note, the following "dangling" symlinks do exist in the root directory:
    initrd.img -> boot/initrd.img-4.15.0-29-generic
    initrd.img.old -> boot/initrd.img-4.15.0-29-generic
    vmlinuz -> boot/vmlinuz-4.15.0-29-generic
    vmlinuz.old -> boot/vmlinuz-4.15.0-29-generic

Notice, these all point to non-existent boot files for kernel 4.15.0-29.