When performing sudo apt-get upgrade from command line nothing to update:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages were automatically installed and are no longer required:
apt-show-versions libapt-pkg-perl libvpx3
Use 'sudo apt autoremove' to remove them.
The following packages have been kept back:
ubuntu-advantage-tools
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
# cat virtualmin.list
deb http://software.virtualmin.com/vm/6/gpl/apt/ virtualmin-xenial main
deb http://software.virtualmin.com/vm/6/gpl/apt/ virtualmin-universal main
Now receive the following:
Reading package lists...
Building dependency tree...
Reading state information...
The following packages were automatically installed and are no longer required:
apt-show-versions libapt-pkg-perl libvpx3
Use 'apt autoremove' to remove them.
The following packages will be upgraded:
webmin-virtual-server
1 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
Need to get 4234 kB of archives.
After this operation, 4096 B of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
webmin-virtual-server
E: There were unauthenticated packages and -y was used without --allow-unauthenticated
# sudo apt-get clean
# sudo apt-get update
W: GPG error: http://software.virtualmin.com/vm/6/gpl/apt virtualmin-xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D9F9010760D62A6B
W: The repository 'http://software.virtualmin.com/vm/6/gpl/apt virtualmin-xenial InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://software.virtualmin.com/vm/6/gpl/apt virtualmin-universal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D9F9010760D62A6B
W: The repository 'http://software.virtualmin.com/vm/6/gpl/apt virtualmin-universal InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
# cat virtualmin.list
deb [signed-by=/usr/share/keyrings/debian-virtualmin-6.gpg] https://software.virtualmin.com/vm/6/gpl/apt virtualmin-xenial main
deb [signed-by=/usr/share/keyrings/debian-virtualmin-6.gpg] https://software.virtualmin.com/vm/6/gpl/apt virtualmin-universal main