Install a specific version of an older package by adding an old mirror

I'm attempting to install a specific version of gcc to Ubuntu 18.04.

By default the version of Ubuntu at the time of this writing is 18.04.5. Installing it with sudo apt-get install gcc-7 results in the following:

user@server:~$ gcc-7 -v
gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04) 
user@server:~$ sudo apt-cache policy gcc-7
gcc-7:
  Installed: 7.5.0-3ubuntu1~18.04
  Candidate: 7.5.0-3ubuntu1~18.04
  Version table:
 *** 7.5.0-3ubuntu1~18.04 500
        500 http://hr.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
        500 http://hr.archive.ubuntu.com/ubuntu bionic-security/main amd64 Packages
     7.3.0-16ubuntu3 500
        500 http://hr.archive.ubuntu.com/ubuntu bionic/main amd64 Packages

Apt recognizes two versions and has installed the 7.5.0-3ubuntu1~18.04 one. I need the version 7.4.0.

I have found a package mirror which has the required package version (gcc-7-multilib_7.4.0-1ubuntu1~18.04.1_amd64.deb) and did the following:

# Add "deb https://mirror.squ.edu.om/ubuntuarchive/ubuntu bionic main restricted multiverse universe" to /etc/apt/sources.list
user@server:~$ sudo apt-get update
user@server:~$ sudo apt-cache policy gcc-7
gcc-7:
  Installed: 7.5.0-3ubuntu1~18.04
  Candidate: 7.5.0-3ubuntu1~18.04
  Version table:
 *** 7.5.0-3ubuntu1~18.04 500
        500 http://hr.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
        500 http://hr.archive.ubuntu.com/ubuntu bionic-security/main amd64 Packages
     7.3.0-16ubuntu3 500
        500 http://hr.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
        500 https://mirror.squ.edu.om/ubuntuarchive/ubuntu bionic/main amd64 Packages

However this only added a new mirror to the 7.3.0-16ubuntu3. It didn't introduce the version 7.4.0-1ubuntu1~18.04 which exists as a package in the mirrors. I expected to see the new versions available.

Am looking for an explanation for this behavior and ways to add the 7.4.0 version?

Here's one way to do it.

1. Look at apt changelog gcc-7-multilib to see which older releases of Ubuntu include version 7.4.0. This avoids a lot of mucking about with broken dependencies. Here's the edited list:

    gcc-7 (7.5.0-1ubuntu1) focal
    gcc-7 (7.4.0-15ubuntu1) focal

    gcc-7 (7.4.0-14ubuntu2) eoan
    gcc-7 (7.4.0-14ubuntu1) eoan
    gcc-7 (7.4.0-12ubuntu2) eoan
    gcc-7 (7.4.0-11ubuntu1) eoan
    gcc-7 (7.4.0-10ubuntu2) eoan
    gcc-7 (7.4.0-9ubuntu1) eoan

    gcc-7 (7.4.0-8ubuntu1) disco
    gcc-7 (7.4.0-7ubuntu1) disco
    gcc-7 (7.4.0-6ubuntu1) disco
    gcc-7 (7.4.0-5ubuntu1) disco
    gcc-7 (7.4.0-4ubuntu1) disco
    gcc-7 (7.4.0-3ubuntu2) disco
    gcc-7 (7.4.0-3ubuntu1) disco
    gcc-7 (7.4.0-2ubuntu1) disco
    gcc-7 (7.4.0-1ubuntu1) disco
    gcc-7 (7.3.0-31ubuntu1) disco

2. You can see that both 19.04 (Disco) and 19.10 (Eoan) shipped with the version you want.

   • Note: Both releases are past End of Life. Neither receives security patches, and neither is supported here at AskUbuntu anymore.

3. Unsupported releases of Ubuntu are available at https://old-releases.ubuntu.com/releases/ . If you decide to use an old release for a specific purpose, run it in a VM and be sensible about its access to your network.