When a dispatcher is configured to manage multiple slaves, each of those slaves operates with the same signature (Image and Flags). Because the log file name is specified in the flags, this means that each of the slaves uses the same log file, and output from multiple slaves is interleaved in a single log file.

To enable separate log files for each slave, a percent character (%) used within the -L flag has special meaning. Each instance of a single “%” character in the -L string is replaced by the unique slave ID number before the log file is opened.