Hey there, let's work through this libc6 version issue step by step. I get why this is confusing—you installed that exact version on staging just 4 weeks ago, so it's frustrating that production can't find it now. Here's what's going on and how to fix it:

Ubuntu's official repositories regularly cycle out older package versions, especially security update builds like the one you're targeting. Even a 4-week-old patch version might have been replaced by a newer security fix, so it's no longer in the default active repositories. But don't worry, we can track it down a few ways:

1. Check and adjust your APT sources #

First, make sure your production server's APT sources include Ubuntu's archive repositories where older versions are stored. Here's how:

• Open your sources list file with sudo nano /etc/apt/sources.list
• Add the following lines (adjust the codename to match your Ubuntu release—libc6 2.31 corresponds to Ubuntu 20.04, codenamed focal):
  deb http://archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse
• Save the file, then run sudo apt update to refresh the package cache
• Try installing again with sudo apt install libc6=2.31-0ubuntu9.15

2. Manually download and install the DEB package #

If the above doesn't work, you can grab the specific package file directly from Ubuntu's official package archive:

• Identify your system architecture by running dpkg --print-architecture (you'll get something like amd64)
• Navigate to Ubuntu's package archive, locate the glibc package group under the main pool, and download the libc6_2.31-0ubuntu9.15_[your-architecture].deb file
• Once downloaded, install it with sudo dpkg -i libc6_2.31-0ubuntu9.15_[your-architecture].deb
• Important note: libc6 is a core system library, so if dpkg reports dependency errors, you'll need to download and install the matching dependent packages from the same archive version first.

3. Match your staging server's repo configuration #

Since staging successfully installed this version 4 weeks ago, check its APT sources by running cat /etc/apt/sources.list on staging, then replicate those sources on your production server. It's possible staging is using a local repository, a pinned archive, or hasn't updated its cache recently—mirroring those settings should let production pull the same version.

4. Pin the package version (to avoid future updates) #

Once you get the version installed, you might want to pin it so APT doesn't automatically upgrade it later. Create a file /etc/apt/preferences.d/libc6-pin with:

Package: libc6
Pin: version 2.31-0ubuntu9.15
Pin-Priority: 1001

This will force APT to keep that specific version unless you explicitly upgrade it.

Just a heads-up: Manually modifying libc6 can be risky since it's critical to the entire system. Make sure you have backups or can roll back if something goes wrong!

备注：内容来源于stack exchange，提问作者Philippe Godfrin