Comment 3 for bug 1855354

Verification complete on trusty:

1) I started two trusty ubuntu-base livefs builds:

$ start-livefs-build --livefs=~mwhudson/+livefs/ubuntu/trusty/docker-ubuntu-core-tests --pocket Updates --metadata project='"ubuntu-base"' --metadata image_format='"plain"'
https://launchpad.net/~mwhudson/+livefs/ubuntu/trusty/docker-ubuntu-core-tests/+build/195865
$ start-livefs-build --livefs=~mwhudson/+livefs/ubuntu/trusty/docker-ubuntu-core-tests --pocket Proposed --metadata project='"ubuntu-base"' --metadata image_format='"plain"'
https://launchpad.net/~mwhudson/+livefs/ubuntu/trusty/docker-ubuntu-core-tests/+build/195866

2) When they'd built, I downloaded the artifacts:

$ wget -O ubuntu-base-trusty-updates.tar.gz https://launchpad.net/~mwhudson/+livefs/ubuntu/trusty/docker-ubuntu-core-tests/+build/195865/+files/livecd.ubuntu-base.rootfs.tar.gz
$ wget -O ubuntu-base-trusty-proposed.tar.gz https://launchpad.net/~mwhudson/+livefs/ubuntu/trusty/docker-ubuntu-core-tests/+build/195866/+files/livecd.ubuntu-base.rootfs.tar.gz

3) I tested them using this silly script:

mwhudson@anduril:~/tmp/trusty-test$ cat test.sh
#!/bin/bash -eux

cleanup () {
    for m in dev/pts dev proc sys; do
        umount chroot/$m
    done
    rm -rf chroot
}
trap cleanup EXIT

mkdir chroot
tar -C chroot -xf "$1"
for m in dev dev/pts proc sys; do
    mount --bind /$m chroot/$m
done
cp /etc/resolv.conf chroot/etc
chroot chroot apt update
chroot chroot apt install -y socat
$

The output is rather verbose so it's here: https://paste.ubuntu.com/p/Mgf6qh2RGx/ but the upshot is that the attempt to install socat failed with the -updates tarball and succeeded with the -proposed tarball.