Running the Linux server build of UE5 and observing that log output to stdout is being flushed every 4k.
Is there a configuration to disable buffering of log output to stdout? If not, what are my options for writing output unbuffered to stdout?
I know I’m necrobumping this but I ran into this also.
It looks like Engine/Source/Runtime/ApplicationCore/Private/Linux/LinuxConsoleOutputDevice.cpp is what’s handling the logging to stdout here. There is no manual flushing so standard stdout buffering will defer here. If you’re running the UE server without a TTY (not via a terminal, e.g. in Kubernetes or Docker), it’s up to the compiler implementation, which typically is 8k or 4k in our case. So you can either attach a TTY to defer to line-buffering (flushes after \n or manually add fflush(stdout) after the printf.
Another potential option is to use the CLI flag -stdout, which will defer to the FOutputDeviceStdOutput device in Engine/Source/Runtime/Launch/Private/LaunchEngineLoop.cpp, which already has a fflush(stdout) after each line, though it seems like the logging is more limited in this mode.
A totally separate solution (which is what I went with) is use a 3rd party program like stdbuf -oL -eL <program> to force line buffering for both stdout and stderr