Also...be sure to turn on logging to file in retroarch
To enable logging in RetroArch, navigate to Settings > Logging and enable both Logging Verbosity and Log to File. Set the Frontend Logging Level and Core Logging Level to your desired verbosity (0 for debug, 1 for info, 2 for warnings, and 3 for errors). After enabling these settings, restart RetroArch and your logs will be written to the /retroarch/logs/
OR you could open your retroarch.cfg manually and find these lines
log_to_file = "false"
Change that to
log_to_file = "true"