The two tokens, header and trailer, are special in that they distinguish the endpoints of an audit record and bracket all the other tokens. A header token begins an audit record. A trailer token ends an audit record. It is an optional token that is added as the last token of each record only when the AUDIT_TRAIL audit policy has been set.
The trailer token is special in that it marks the termination of an audit record. Together with the header token, the trailer token delimits an audit record. The trailer token supports backward seeks of the audit trail. The trailer token has three fields: a token ID that identifies this token as a trailer token, a pad number to aid in marking the end of the record, and the total number of characters in the audit record, including both the header and trailer tokens. Figure A-27 shows a trailer token.
The audit trail analysis software ensures that each record contains both header and trailer. In the case of a write error, as when a file system becomes full, an audit record can be incomplete and truncated. auditsvc, the system call responsible for writing data to the audit trail, attempts to put out complete audit records. See the auditsvc(2) man page. When file system space runs out, the call terminates without releasing the current audit record. When the call resumes, it can then repeat the truncated record.