Question about why the `apt` package manager might install an older version of a package when a newer version is available from external sources. This can happen due to various reasons, and here's an explanation:
1. **Repository Priority**: The behavior of `apt` depends on the priority of repositories. Debian-based systems like Ubuntu use a system of priorities to determine which package versions to install. The distribution's official repositories typically have higher priority, and external or third-party repositories may have lower priority.
2. **Pin Priority**: You can assign pin priorities to specific repositories or packages using `/etc/apt/preferences` or `/etc/apt/preferences.d` files. These pinning preferences can override the default priorities set by `apt`. If you have such preferences set, it can influence which versions of packages are installed.
3. **Package Pinning**: Sometimes, specific package versions may be pinned to avoid conflicts or issues with other packages. This is often done for stability and compatibility reasons. In such cases, `apt` will install the pinned version even if a newer one is available.
4. **Repository Updates**: `apt` relies on package metadata and information provided by the repositories. If the repository has not updated its package information to include the newer version, `apt` won't be aware of it.
5. **Dependency Resolution**: `apt` also considers package dependencies. If the newer version has dependencies that are not available or compatible with the rest of your system, `apt` may opt to install an older version to maintain package compatibility.
6. **Local Packages**: Sometimes, you may have locally stored packages that take precedence over repository versions. If `apt` finds a locally stored older version, it might use that instead.
To ensure that `apt` installs the most up-to-date version of a package from external sources, you can do the following:
1. Make sure the external repository is correctly configured and enabled.
2. Use the `-t` or `--target-release` option with `apt` to specify the release from which to install packages. This allows you to request packages from a specific repository or release.
3. Review and adjust any pinning or preference settings in your `/etc/apt/preferences` and `/etc/apt/preferences.d` files.
4. Ensure that the newer version you want is available in the external repository and that the repository has been updated.
By carefully configuring your repository preferences and using the appropriate `apt` options, you can influence the package versions that are installed on your system.