The Linux Audit subsystem provides a secure logging framework that is used to capture and record security relevant events. It consists of a kernel component which generates audit records based on system activity, a userspace daemon which logs these records to a local file or a remote aggregation server, and a set of userspace tools to for audit log inspection and post-processing.
The main Linux Kernel README can be found at Documentation/admin-guide/README.rst
The canonical audit kernel repository is hosted by kernel.org:
There is also an officially maintained GitHub mirror:
The audit userspace tools and test suites are hosted by GitHub: