Legato's runtime architecture manages each application in its own sandbox.

Applications communicate with each other using access-controlled message-passing services. The Supervisor automatically creates sandboxes.

Supervisor

The Supervisor is a privileged process running on the target device that:

creates and destroys sandboxes for applications
starts and stops applications
acts as an application watchdog
performs fault recovery actions when applications fail (such as restarting the app).

Log Control Daemon

The Log Control Daemon provides a user-friendly way to control log message filtering for running Legato application processes.

See Logging API

Service Directory

The Service Directory provides a secure way for client processes to find servers that offer the services they need. The Service Directory ensures that only authorized connections are established.

See Services and Interfaces

Configuration Tree

The Configuration Tree provides persistent configuration data storage organized in a tree structure.

See Configuration and Configuration Tree API

Applications

An application is a collection of executable files, libraries, and/or other resource files (e.g., audio files, web pages) that can be deployed to a target device. Once installed on a device, an application can be started and stopped.

By default, each application runs in its own sandbox. When an application is constructed, all the files and IPC services it needs to access are declared (these should be examined and approved before installed on the target). At runtime, the Supervisor and the Service Directory enforce that only those approved files and IPC services are accessed by that application.

Watchdog

Legato has a service that provides a kickable watchdog with a timeout that can be configured in Application Definition (.adef) Files or specified at run time. If a kick is not received in the specified time out, the supervisor signals to perform the action given in WatchdogAction. Applications are assembled from components.

What's Next?

Components