11.4. Log Files

Unless Exim has been configured to use only syslog, it writes logging data to three files in its log directory, whose location is configurable at build time or at runtime. The most common locations are the log subdirectory within Exim's spool directory (which is the default), or a location such as /var/log/exim on systems that keep all their logs in one place. The contents of Exim's logs are described in Section 21.1, in Chapter 21.

Exim processes all write to the same log files, but no Exim process ever reads any log data. Interlocking between processes is achieved by opening log files for appending, and ensuring that each log line is written in a single write operation. The operating system then ensures that only one update happens at once, and there is no need for the processes to do any locking of their own.