APT Repositories

APT Repositories

Debian and systems based on it like Ubuntu, Linux Mint, and Raspbian use the same package management system. APT (Advanced Package Tool) is a set of tools for managing Debian packages, and therefore the applications installed on your Debian system. It provides a wide set of operations like searching repositories, installing packages with their dependencies, and managing upgrades.

See APT Documentation

Nexus Repository supports the APT repository format for proxy and hosted repositories.

Proxying APT Repositories

You may set up an APT proxy repository to access a remote repository location.

Minimal configuration steps are:

Note
This field is optional unless Enforce Distribution is enabled. When Enforce Distribution is enabled, it restricts client access to a single, explicitly configured distribution.

Configuration Options

When signing is enabled, import the Nexus public key:

apt-key add <public-key>

APT Proxy Behavior

  1. Passthrough Mode

    • Configuration: 
      Signing: not configured
    • Behavior:
      • Metadata is served from upstream
      • No metadata is generated
      • Packages are cached
    • Example: 
      deb http://nexus/repository/apt-proxy jammy main

  2. Re-signing Mode (Single Distribution)

    • Configuration: 
      Signing: configured
Distribution: jammy
    • Behavior:
      • Nexus generates and signs metadata
      • Applies only to configured distribution
      • Metadata includes upstream + cached packages
      • Initial requests may still use upstream metadata
    • Example: 
      # Import Nexus public key  
curl http://nexus/repository/apt-proxy/gpg.key | apt-key add -

      # Add to sources.list  
deb http://nexus/repository/apt-proxy jammy main

  3. Re-signing Mode (Multi-Distribution)

    • Configuration: 
      Signing: configured
Distribution: not set
    • Behavior:
      • Distributions are tracked when accessed
      • Metadata generated per distribution
      • Supports multiple distributions
    • Example: 
      deb http://nexus/repository/apt-proxy jammy main
deb http://nexus/repository/apt-proxy focal main

  4. Enforce Distribution

    • Enabled with Distribution
      • Only configured distribution is allowed
      • Other distributions return HTTP 404
    • Enabled without Distribution
      • This is a misconfiguration
      • Requests are still allowed (fail-open behavior)

Runtime Behavior

Flat Repository Formats

A flat repository does not use the dists hierarchy of directories and instead places meta index and indices directly into the archive root (or some part below it). In sources.list syntax, a flat repository is specified like this:

 deb uri directory/

Where URI specifies the archive root, and the directory specifies the position of the meta index and the indices relative to the archive root. In Flat repositories, the following indices are supported:

InRelease, Release, Release.gpg meta-information, and indices differences are supported. Translations and Contents indices are not defined. Indices may be compressed just like in the standard Debian repository format.

See Flat Repository Format

Hosting Apt Repositories

You may use a hosted APT repository to upload internally developed and third-party packages.

When creating a hosted APT repository, you need to generate a GPG signing key pair or use an existing one. Hosted APT repositories only sign the metadata. Nexus Repository does not sign packages.

Generate a key pair in a Linux system with the following commands:

apt-get update
apt-get install gpg
gpg --gen-key
gpg --list-keys
cd <path to the folder to import the key pair>
gpg --armor --output public.gpg.key --export <gpg key Id>
gpg --armor --output private.gpg.key --export-secret-key <gpg key Id>

A key ID looks like: '515F58C16D58E682E91ACEFF17B5C97F9A816AD7'

Minimal configuration steps are:

To use a hosted APT repository you need to export the GPG public key into your Linux system. Use the public key (public.gpg.key) from the key pair generated above.

apt-get update
apt-get install gnupg
apt-key add <full folder path in the container>/public.gpg.key

Updating GPG Keys

GPG (GNU Privacy Guard) keys may be set to expire, and it is generally considered a best practice to do so. When updating the GPG keys, the metadata of Nexus Repository needs to be rebuilt to sign it with the new key.

You may do this by running the Apt - Rebuild Apt metadata task after replacing the GPG Key.

See the topic Tasks: APT Rebuild Apt metadata

Deploying Packages to Hosted APT Repositories

You can use HTTP POST or Upload in the UI to upload packages to a hosted APT repository.

The following example uses a curl command to upload a test.deb file to a hosted APT repository:

curl -u "admin:admin123" -H "Content-Type: multipart/form-data" --data-binary "@./test.deb" "http://localhost:8081/repository/apt-hosted/"

Browsing APT Repositories and Searching Packages

You can browse APT repositories in the user interface inspecting the components and assets and their details, as described in Browsing Repositories and Repository Groups. Searching for APT packages can be performed in the user interface, too. It finds all packages that are currently stored in the repository manager, as described in Searching for Components.

Configuring APT Client

If you already loaded a metadata using apt update commands first clean it by removing all files from /var/lib/apt/lists/.

To configure the APT client to work with Nexus Repository Manager edit the file /etc/apt/sources.list. Add the following line if you want to add the repository to the list, or replace the content of the file if you're going to use only your repository:

deb <repository URL> <distribution> main

For a hosted repository you should use the from the repository properties. For a proxy repository, the should be the same as in the original remote repository settings.

You can get the from the table in Browsing Repositories and Repository Groups via the UI.

Taking a Snapshot of Repository Metadata

A snapshot in terms of the APT repository is a named static copy of the metadata of the repository. Changes in the repository will not cause any changes in the snapshot. A snapshot does NOT contain any binary files. So be ready if the content of the repository changes the snapshot can include some invalid metadata.

Available snapshots can be viewed in UI Browse in the /snapshots folder. Files of a particular snapshot are available in /snapshots/ folder.

Snapshots functionality is available for both proxy and hosted repositories.

You can use a snapshot to set up an APT client. The URL of the snapshot is <URL of the repository>/snapshots/<snapshot Id>. For example http://localhost:8081/repository/apt-proxy/snapshots/release123.

Snapshot functionality is useful in the following cases:

Note
To use the removed in the remote repository package, this package must be cached in the proxy repository. If not, you are aware of the changed remote repository, the updated package will not be installed.

There are two variants to create a snapshot:

curl -u "admin:admin123" -X MKCOL "http://localhost:8081/repository/apt-proxy/snapshots/release123"
  1. Create a filter. This is a text file with the following format:
Architectures: <list of architectures>
Components: <list of components>

For example:

Architectures: i386
Components: restricted universe
  1. Use HTTP PUT request to snapshot a filtered metadata. This example uses curl to create a snapshot of repository apt-proxy with filter stored in filter.txt and id filtered_snapshot:
curl -u "admin:admin123" -X PUT -H "Content-Type: multipart/form-data" -T "filter.txt" "http://localhost:8081/repository/apt-proxy/snapshots/filtered_snapshot"

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