Why is my Elementary OS Not Updating via terminal / Apps are not updating from App Center?

Question

I am not able to update apps or the OS. While upgrading from the terminal, I am getting this error message:

Do you want to continue? [Y/n] y 

(Reading database ... 271161 files and directories currently installed.)
Preparing to unpack .../appstream-data-pantheon_0.3.0-0~14~ubuntu0.4.1_all.deb ...

Unpacking appstream-data-pantheon (0.3.0-0~14~ubuntu0.4.1) ...

dpkg: error processing archive /var/cache/apt/archives/appstream-data-pantheon_0.3.0-0~14~ubuntu0.4.1_all.deb (--unpack):

 trying to overwrite '/usr/share/app-info/yaml/pantheon_xenial-main_amd64.yml.gz', which is also in package appstream-data-pantheon-loki-stable 0.4+r13~ubuntu0.4.1

Processing triggers for appstream (0.10.6-1~ubuntu16.04.2) ...

AppStream cache update completed successfully.

Errors were encountered while processing:
 /var/cache/apt/archives/appstream-data-pantheon_0.3.0-0~14~ubuntu0.4.1_all.deb

E: Sub-process /usr/bin/dpkg returned an error code (1)

Answer 1

To solve the problem "public key is not available: NO_PUBKEY A74F73EFFE70B91C", import the key:

wget -q "http://packages.elementary.io/key.asc" -O- | sudo apt-key add -

Answer 2

Following what I've found about these topics, I think you either need to remove the conflicting package, or you need to overwrite it explicitly (I have no idea why its not an option that pops up while you are trying to install):

sudo dpkg -i --force-overwrite /var/cache/apt/archives/appstream-data-pantheon_0.3.0-0~14~ubuntu0.4.1_all.deb

(source)

Answer 3

This will be a late reply, but here's how I fixed this problem:

• Removed the problematic URL lists from the /etc/apt/sources.list file
• Rebooted the machine
• Re-added the URL lists back to the /etc/apt/sources.list file with appropriate URLs

This helped me download latest updates from elementary software, and is how I fixed the problem.