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Extensions

Unlike conventional embedded Linux distributions, Avocado uses a sophisticated layered architecture. An immutable, cryptographically verifiable base system combines with composable System Extensions (sysext) and Configuration Extensions (confext) to enable applications and services as self-contained, isolated components. This design delivers web development-like iteration speeds through live NFS-mounted extensions and hardware-in-the-loop debugging.

System Extensions (sysext)​

System Extensions dynamically extend the /usr/ and /opt/ directory hierarchies at runtime without modifying the base system. Extensions contain files structured like a regular OS tree, combined with the host OS using overlayfs when activated during boot.

Extensions can be provided as plain directories, btrfs subvolumes, or disk images (GPT-partitioned or raw filesystems like squashfs/erofs). They're automatically activated by systemd-sysext after filesystems mount but before basic.target, ensuring extended functionality is available when services initialize.

Configuration Extensions (confext)​

Configuration Extensions operate exclusively on the /etc/ hierarchy, enabling runtime reconfiguration of OS services without deploying new code or complete OS updates. This allows independent management of system configuration, security policies, and environment-specific settings.

Development workflow​

The extension system transforms embedded development from edit-compile-flash-boot-test cycles into interactive workflows:

  • Live NFS-mounted extensions: Changes reflect immediately on target devices
  • Interactive debugging: GDB server integration with live code updates
  • Hot reloading: Update application code without losing system state

Learn how to leverage these capabilities with hardware-in-the-loop development, which enables web development-like iteration speeds on embedded devices.

Extensions integrate with Avocado's SDK for declarative package selection, custom toolchain extensions, and versioned dependencies across development environments.

Security and composition​

Extensions maintain security through compatibility enforcement via release files, cryptographic signature verification, and integrity checking during runtime. Multiple extensions compose together with clear isolation boundaries - each contains complete dependencies and cannot modify the immutable base system.

A typical composition might include:

Base Avocado OS
├── Container runtime extension
├── AI framework extension
├── Networking tools extension
└── Custom application extension

Extensions enable atomic updates, independent rollback capability, and staged deployment across device fleets while maintaining the same composability and security properties from development through production.