I am getting this message when installing a .deb file:
Download is performed unsandboxed as root as file '/home/joesph-russ-bryant/teamviewer_amd64.deb' couldn't be accessed by user '\_apt'. - pkgAcquire::Run (13: Permission denied)
What causes this, and how do I fix it?
When apt runs, it runs in a 'sandboxed' user named _apt behind the scenes underneath the apt and superuser powers. That 'sandboxed' user can still do things with packages, system access, etc. but it's utilized under the hood and limited in what all it actually can access, intentionally.
However, this sandboxing and control only works when apt is handling installation from the configured repositories, as it can download files into temporary space that utilizes the _apt sandbox user.
When you install a .deb from your filesystem (/home/user/Downloads, /tmp/, anything on your system locally anywhere else outside of standard apt repository downloads, etc), the sandboxed _apt user is not capable of being used to handle proper access permissions to access files elsewhere in the filesystem.
This is why you get the warning-level notification* about couldn't be accessed by user '_apt'.
However, despite receiving this warning, there is actually nothing wrong at all. And you can safely ignore that warning when installing .deb files from your filesystem space and not from apt downloading it from an apt repository configured on your system.
You can't disable the warning, but you also can safely ignore it in this case.
