Merge pull request #6196 from CatherineF-dev/patch-1

Add logging header formats in doc

Author: k8s-ci-robot

contributors/devel/sig-instrumentation/logging.md

@@ -38,3 +38,25 @@ Logs generated by `ErrorS` command may be enhanced with additional debug informa
 As per the comments, the practical default level is V(2). Developers and QE
 environments may wish to run at V(3) or V(4). If you wish to change the log
 level, you can pass in `-v=X` where X is the desired maximum level to log.
+
+## Logging header formats
+
+An example logging message is
+```
+I0528 19:15:22.737538   47512 logtest.go:52] msg...
+```
+
+This log line have this form:
+```
+	Lmmdd hh:mm:ss.uuuuuu threadid file:line] msg...
+where the fields are defined as follows:
+	L                A single character, representing the log level (eg 'I' for INFO)
+	mm               The month (zero padded; ie May is '05')
+	dd               The day (zero padded)
+	hh:mm:ss.uuuuuu  Time in hours, minutes and fractional seconds
+	threadid         The space-padded thread ID as returned by GetTID()
+	file             The file name
+	line             The line number
+	msg              The user-supplied message
+```
+See more in [here](https://github.com/kubernetes/klog/blob/9ad246211af1ed84621ee94a26fcce0038b69cd1/klog.go#L581-L597)