The log write path for applications inside a container is determined by the log framework configuration it used. The log level (such as info or error) is independent of container standard output (stdout) or error output (stderr) type.

If the log framework calls os.Stdout, the log is written to the container's standard output (stdout).

If the log framework calls os.Stderr, the log is written to the container's standard error output (stderr).

Notice

If the logging framework configuration is unclear, it is recommend to collect both stdout and stderr.

View the log write pathway based on framework configuration

Taking a Golang application as an example:

Logger is configured with logger.SetOutput(os.Stderr), so all logs (including info and error levels) are written to standard error output (stderr).

logger := logrus.New()​
logger.SetOutput(os.Stderr)  # Log is redirect to stderr​
logger.SetLevel(logrus.DebugLevel)​
logger.Info("Service started")  # write in stderr​
logger.Error("Disk full")  # write in stderr​

View the log write pathway based on log content

Taking the Containerd container runtime as an example:

Check the /var/log/pods/<namespace>_<pod-name>_<pod-uid>/<container-name>/0.log log file. In the file, the stderr label indicates that logs are written to the standard error output (stderr).

2025-05-12T10:39:39.477327246+08:00 stderr F 10.1.0.138 - - [12/May/2025 02:39:39] "GET / HTTP/1.1" 200 -​
2025-05-12T10:39:40.23676878+08:00 stderr F 10.1.0.138 - - [12/May/2025 02:39:40] "GET / HTTP/1.1" 200 -​
2025-05-12T10:39:49.477228162+08:00 stderr F 10.1.0.138 - - [12/May/2025 02:39:49] "GET / HTTP/1.1" 200 -​

Last updated: 2025.12.15 17:27:03

Public security network record in Beijing: No. 11010802032137