As per the subject, on Windows this doesn’t work since it doesn’t support “line”, it will just go to full buffering. See: https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/setvbuf?view=msvc-160#remarks > For some systems, this provides line buffering. However, for Win32, the behavior > is the same as _IOFBF - Full Buffering. Not really a bug or something, just wanted to call it out here in case it is worthy of a mention in the manual wrt platform differences. Thijs Source: https://github.com/lunarmodules/lualogging/pull/9