The name of a files used to log failed Accounting-Request messages in the standard radius accounting log format. If no reply is ever received from any of the remote hosts, the accounting message is logged to the named file. For more information about log file format, see Section 9.5. Accounting log file. If no AcctFailedLogFileName is defined, failed accounting messages are not logged. The default is no logging. The file name can include special formatting characters as described in Section 3.3. Special formatters, which means that, for example, using the %c specifier, you can maintain separate accounting log files for each Client. The AcctFailedLogFileName file is always opened, written and closed for each failure, so you can safely rotate it at any time.

The user name that is recorded in the log file is the rewritten user name when RewriteUsername is enabled.

# Log all accounting to a single log file in LogDir
AcctFailedLogFileName %L/misseddetails