For now, all run history is written to a flat file. The file name (and location) is defined in the environment variable UBOONEDAQRUNFILE. Run information is separated by a line of 40 '#' characters. Run information will be appended to this file at the start of a run (BeginRun). The next run number is determined by going to the end of the run history file and reading backwards until the last run number is found. The default first run number is 10000.