W: Download is performed unsandboxed as root as file '/var/cache/apt/archives/partial/ couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)

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 https://askubuntu.com/questions/908800/what-does-this-apt-error-message-download-is-performed-unsandboxed-as-root

W: Download is performed unsandboxed as root as file '/var/cache/apt/archives/partial/samba-libs_2%3a4.5.8+dfsg-0ubuntu0.17.04.1_i386.deb' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)

Usually apt uses the user _apt to download packages. In your case _apt doesn't have write permission to either /var/cache/apt/archives/partial/ or an existing file /var/cache/apt/archives/partial/samba-libs_2%3a4.5.8+dfsg-0ubuntu0.17.04.1_i386.deb so it downloaded the file as root.

Make sure /var/cache/apt/archives/partial/ and everything below it are writeable for _apt, e.g. by running

sudo chown -Rv _apt:root /var/cache/apt/archives/partial/
sudo chmod -Rv 700 /var/cache/apt/archives/partial/