How to fix E: Version 'x.x.x' for 'package-name' was not found in APT

First, check what versions are actually available in your repositories using apt-cache:

apt-cache policy package-name

This command shows all available versions with their sources. For example, if you run this for Docker:

apt-cache policy docker-ce

You will see output like:

docker-ce:
  Installed: (none)
  Candidate: 5:24.0.6~3-0~ubuntu-focal
  Version table:
     5:24.0.6~3-0~ubuntu-focal 500
        500 https://download.docker.com/linux/ubuntu focal/stable amd64 Packages
     5:24.0.5~3-0~ubuntu-focal 500
        500 https://download.docker.com/linux/ubuntu focal/stable amd64 Packages

Notice the exact format including colons, tildes, and build numbers.

The version you install must match exactly what appears in the apt-cache output. Do not simplify or abbreviate the version number. For example:

Incorrect (will fail):

sudo apt install docker-ce=18.03.0.ce

Correct:

sudo apt install docker-ce=5:18.03.0~ce-0~ubuntu

Note the differences:
- Colons (epoch): 5:
- Tildes instead of dots: ~ce instead of .ce
- Build designation: -0~ubuntu

Always copy the complete version string from apt-cache policy output.

If you cannot find the version you need, your package cache may be outdated. Update it:

sudo apt update

This command refreshes your local cache of available packages from all enabled repositories. Sometimes newly released versions or older versions are added back to repositories, and you need to update to see them.

Some versions may only be available for specific Ubuntu/Debian versions. Check your current distribution:

lsb_release -a

Or more concisely:

lsb_release -cs

When searching for packages online (e.g., at packages.ubuntu.com), make sure you select the correct distribution version. A version available for Ubuntu 20.04 (Focal) may not be available for Ubuntu 22.04 (Jammy).

If the version you need is from a PPA or third-party repository that you removed or disabled:

sudo add-apt-repository ppa:owner/ppa-name
sudo apt update
apt-cache policy package-name

Then install using the exact version from the new apt-cache output:

sudo apt install package-name=x.x.x

You can also check what PPAs are enabled:

add-apt-repository --list | grep ppa

Once you have confirmed the exact version string from apt-cache policy, install it:

sudo apt install package-name=exact.version.string

For example:

sudo apt install nginx=1.18.0-6ubuntu14.4

The installation should succeed if the version string is exact. If it still fails, double-check the version string character-by-character against the apt-cache output.