Comment 0 for bug 1715012

From the upstream report at https://github.com/CanonicalLtd/ubuntu-advantage-script/issues/54:

I tried to enable livepatch on a trusty machine, but it got stuck:

ubuntu@61-b1:~$ sudo ubuntu-advantage enable-livepatch <redacted>
Installing missing dependency snapd...

Behind the scenes, what happened is that dpkg issued a prompt:

2228 pts/0 S+ 0:00 | \_ sudo ubuntu-advantage enable-livepatch redacted
2229 pts/0 S+ 0:00 | \_ /bin/sh -e /usr/bin/ubuntu-advantage enable-livepatch redacted
2236 pts/0 S+ 0:01 | \_ apt-get install -y snapd
3269 pts/0 S+ 0:00 | \_ /usr/bin/dpkg --status-fd 43 --configure liblzo2-2:amd64 libsystemd-journal0:amd64 linux-image-4.4.0-92-generic:amd64 linux-image-extra-4.4.0-92-generic:amd64 linux-image-generic-lts-xenial:amd64 linux-headers-4.4.0-92:all linux-headers-4.4.0-92-generic:amd64 linux-headers-generic-lts-xenial:amd64 linux-generic-lts-xenial:amd64 cgroup-lite:all squashfs-tools:amd64 systemd:amd64 snapd:amd64 thermald:amd64
3278 pts/0 S+ 0:00 | \_ /usr/bin/perl /var/lib/dpkg/info/linux-image-4.4.0-92-generic.postinst configure
3304 pts/0 S+ 0:00 | \_ run-parts --verbose --exit-on-error --arg=4.4.0-92-generic --arg=/boot/vmlinuz-4.4.0-92-generic /etc/kernel/postinst.d
11905 pts/0 S+ 0:00 | \_ /usr/bin/perl -w /usr/share/debconf/frontend /usr/sbin/update-grub-legacy-ec2
11911 pts/0 S+ 0:00 | \_ /bin/bash /usr/sbin/update-grub-legacy-ec2
12312 pts/0 S+ 0:00 | | \_ /bin/bash /usr/bin/ucf --debconf-ok --debconf-template grub/update_grub_changeprompt_threeway --three-way /tmp/filez4NBAU /var/run/grub/menu.lst
12362 pts/0 S+ 0:00 | \_ whiptail --backtitle Package configuration --title --output-fd 11 --nocancel --default-item keep the local version currently installed --menu A new version of /boot/grub/menu.lst is available, but the version installed currently has been locally modified. What would you like to do about menu.lst? 17 118 7 -- install the package maintainer's version keep the local version currently installed show the differences between the versions show a side-by-side difference between the versions show a 3-way difference between available versions do a 3-way merge between available versions (experimental) start a new shell to examine the situation
Hitting ENTER at the stuck screen accepted whatever was the default choice and moved on.

Note that this can happen in any Ubuntu release, not just trusty.