How to set up a proxy on Debian?

Question

Debian

I installed Debian 10 on VirtualBox, on the network to which I am connected to access the Internet (and only there is a repository there), I can’t set up a proxy, although I set up cntlm on a neighboring PC and through it I work quietly on Windows, which is also installed on VirtualBox next door with Debian. When installing Debian, I tried to register a proxy, but for some reason it does not work on Debian, or I chose the wrong repository :(
For example, this is what it now writes in response to the apt-get update command:

Answer 1

your system is trying to upgrade from the CD-ROM.
and comment out the lines starting with deb cdrom ... to make it look like this - #deb cdrom .... Uncomment
the rest of the lines starting with deb and deb-src .
but in general, if you use a proxy on your network, then look at the settings in VirtualBox itself. like they should be there.

Answer 2

Is the proxy registered in HTTP_PROXY?

Answer 3

export HTTP_PROXY=scheme://host:port