Logtostderr

Logtostderr is a command-line flag used by Google's glog logging library to direct all log output to the standard error stream rather than to log files. When this flag is enabled, log messages of all severities (INFO, WARNING, ERROR, FATAL) are written to standard error, and no log files are created or rotated in a log directory. This behavior makes it suitable for environments where logs are collected from stdout or stderr, such as containers or centralized logging systems.

Usage and behavior: Programs that use glog accept the flag as -logtostderr. It can be combined with other glog flags, such as -v for verbose logging. Importantly, -logtostderr disables file-based logging; setting a log_dir or other file-oriented options will not produce log files when this flag is active. Some setups also offer -alsologtostderr, which logs to both standard error and log files when file logging is enabled; however, if -logtostderr is set, the output typically goes to standard error only.

Format and scope: Log messages preserve glog’s standard formatting, including timestamps, severity labels, and the source location. The flag is widely used in Go-based and C++ projects leveraging glog, including many Kubernetes components, where log collection through standard streams is preferred.

Origins and relation: Logtostderr originates from the Google glog library. It is one of several logging direction flags, alongside options for file logging and verbose levels. See also: glog, -alsologtostderr, -log_dir, -stderrthreshold, -v.