Ah, "apt-cache show" can probably see it because it's installed locally maybe? I don't see the updates pocket in /var/lib/apt/lists/:
phablet@ubuntu-phablet:/var/lib/apt/lists$ ls lock partial ports.ubuntu.com_ubuntu-ports_dists_vivid_Release ports.ubuntu.com_ubuntu-ports_dists_vivid_Release.gpg ports.ubuntu.com_ubuntu-ports_dists_vivid_main_binary-armhf_Packages ports.ubuntu.com_ubuntu-ports_dists_vivid_main_i18n_Translation-en ports.ubuntu.com_ubuntu-ports_dists_vivid_restricted_binary-armhf_Packages ports.ubuntu.com_ubuntu-ports_dists_vivid_restricted_i18n_Translation-en ports.ubuntu.com_ubuntu-ports_dists_vivid_universe_binary-armhf_Packages ports.ubuntu.com_ubuntu-ports_dists_vivid_universe_i18n_Translation-en ppa.launchpad.net_ci-train-ppa-service_stable-snapshot_ubuntu_dists_vivid_Release ppa.launchpad.net_ci-train-ppa-service_stable-snapshot_ubuntu_dists_vivid_Release.gpg ppa.launchpad.net_ci-train-ppa-service_stable-snapshot_ubuntu_dists_vivid_main_binary-armhf_Packages ppa.launchpad.net_ci-train-ppa-service_stable-snapshot_ubuntu_dists_vivid_main_i18n_Translation-en
However sources.list does have "deb http://ports.ubuntu.com/ubuntu-ports/ vivid-updates universe" but maybe it wasn't present during image generation.
Ah, "apt-cache show" can probably see it because it's installed locally maybe? I don't see the updates pocket in /var/lib/ apt/lists/ :
phablet@ ubuntu- phablet: /var/lib/ apt/lists$ ls com_ubuntu- ports_dists_ vivid_Release com_ubuntu- ports_dists_ vivid_Release. gpg com_ubuntu- ports_dists_ vivid_main_ binary- armhf_Packages com_ubuntu- ports_dists_ vivid_main_ i18n_Translatio n-en com_ubuntu- ports_dists_ vivid_restricte d_binary- armhf_Packages com_ubuntu- ports_dists_ vivid_restricte d_i18n_ Translation- en com_ubuntu- ports_dists_ vivid_universe_ binary- armhf_Packages com_ubuntu- ports_dists_ vivid_universe_ i18n_Translatio n-en net_ci- train-ppa- service_ stable- snapshot_ ubuntu_ dists_vivid_ Release net_ci- train-ppa- service_ stable- snapshot_ ubuntu_ dists_vivid_ Release. gpg net_ci- train-ppa- service_ stable- snapshot_ ubuntu_ dists_vivid_ main_binary- armhf_Packages net_ci- train-ppa- service_ stable- snapshot_ ubuntu_ dists_vivid_ main_i18n_ Translation- en
lock
partial
ports.ubuntu.
ports.ubuntu.
ports.ubuntu.
ports.ubuntu.
ports.ubuntu.
ports.ubuntu.
ports.ubuntu.
ports.ubuntu.
ppa.launchpad.
ppa.launchpad.
ppa.launchpad.
ppa.launchpad.
However sources.list does have "deb http:// ports.ubuntu. com/ubuntu- ports/ vivid-updates universe" but maybe it wasn't present during image generation.