Error encountered during apt install indicated that the file couldn't be accessed by user _apt
When installing package from local file (.deb file), following error might be occurred.
Processing triggers for dbus (1.14.0-2ubuntu3) ...
N: Download is performed unsandboxed as root as file 'full_path_of_deb_file_name' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)Usually apt tries to run the process that fetches packages as a different user called _apt to increase security. That's no problem if it has to download packages from the internet. But if you tell it to install a .deb file that's already on your system, it needs to have permission to access that file by _apt user. Otherwise, above error will be shown.