Linux Unsupported proxy configured [closed]

Question

I'm new in linux, I just started using debian. I tried to install g++, by

apt-get install g++

but it didn't work

root@HP:/home/krzysztof# apt-get install g++
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following additional packages will be installed:
  g++-6 libstdc++-6-dev
Suggested packages:
  g++-multilib g++-6-multilib gcc-6-doc libstdc++6-6-dbg libstdc++-6-doc
The following NEW packages will be installed:
  g++ g++-6 libstdc++-6-dev
0 upgraded, 3 newly installed, 0 to remove and 0 not upgraded.
Need to get 8,516 kB of archives.
After this operation, 39.8 MB of additional disk space will be used.
Do you want to continue? [Y/n] Y
Err:1 http://ftp.pl.debian.org/debian stretch/main amd64 libstdc++-6-dev             amd64 6.3.0-18+deb9u1
  Unsupported proxy configured: 127.0.0.1://8888
Ign:2 http://ftp.pl.debian.org/debian stretch/main amd64 g++-6 amd64     6.3.0-18+deb9u1
Err:3 http://ftp.pl.debian.org/debian stretch/main amd64 g++ amd64 4:6.3.0-4
  Unsupported proxy configured: 127.0.0.1://8888
Err:1 http://security.debian.org/debian-security stretch/updates/main     amd64 libstdc++-6-dev amd64 6.3.0-18+deb9u1
  Unsupported proxy configured: 127.0.0.1://8888
Err:2 http://security.debian.org/debian-security stretch/updates/main     amd64 g++-6 amd64 6.3.0-18+deb9u1
  Unsupported proxy configured: 127.0.0.1://8888
E: Failed to fetch http://security.debian.org/debian-    security/pool/updates/main/g/gcc-6/libstdc++-6-dev_6.3.0-18+deb9u1_amd64.deb          Unsupported proxy configured: 127.0.0.1://8888
E: Failed to fetch http://security.debian.org/debian-    security/pool/updates/main/g/gcc-6/g++-6_6.3.0-18+deb9u1_amd64.deb      Unsupported proxy configured: 127.0.0.1://8888
E: Failed to fetch http://ftp.pl.debian.org/debian/pool/main/g/gcc-    defaults/g++_6.3.0-4_amd64.deb  Unsupported proxy configured:     127.0.0.1://8888
E: Unable to fetch some archives, maybe run apt-get update or try with --    fix-missing?

Answer 1

The "//" is a clue that you have left the "http://" off the beginning of the proxy configuration

For example:

Acquire::http::Proxy "127.0.0.1:8888/"

will give the error Unsupported proxy configured: 127.0.0.1://8888, whereas

Acquire::http::Proxy "http://127.0.0.1:8888/"

will correctly set the proxy

Answer 2

Create file /etc/apt/apt.conf and add following content:

 "http://<IP>:<PORT>/";