尝试从未签名的存储库安装Debian软件包到Debian 9:
# apt-get --allow-unauthenticated update
Get:1 http://files.freeswitch.org/repo/deb/freeswitch-1.8 stretch InRelease [3,196 B]
Hit:2 http://security.debian.org/debian-security stretch/updates InRelease
Ign:1 http://files.freeswitch.org/repo/deb/freeswitch-1.8 stretch InRelease
Ign:3 http://debianmirror.nkn.in/debian stretch InRelease
Hit:4 http://debianmirror.nkn.in/debian stretch Release
Fetched 3,196 B in 1s (1,940 B/s)
Reading package lists... Done
W: GPG error: http://files.freeswitch.org/repo/deb/freeswitch-1.8 stretch InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY BD3189F5A2B57698
W: The repository 'http://files.freeswitch.org/repo/deb/freeswitch-1.8 stretch InRelease' is not signed.
N: Data from such a repository can't be authenticated and is …