Manually sending logs to stdout in a container.

Manually sending logs to stdout in a container.

When working with Docker containers, there may be times when you need to pass information to the Docker logging system. Although there are various methods to achieve this, one intriguing approach involves using the special /proc filesystem.

The /proc directory is a unique area in Unix-like systems, containing information about running processes. For Docker containers, the process with an identifier of PID 1 is the main process launched within the container. Its standard output can be accessed as /proc/1/fd/1.

The command echo "test log1" >> /proc/1/fd/1 appends the string “test log1” to the standard output stream of the main process in the container. In practice, this string will be written into the Docker logging system.

To view this log, you can use the command docker logs [container_name]. In this way, you can inspect information passed to /proc/1/fd/1.

However, this is a command that requires appropriate permissions within the container. In practice, you need to have root privileges to write directly to /proc/1/fd/1.

In conclusion, utilizing /proc/1/fd/1 is an intriguing and useful approach for directly passing logs to Docker’s logging system. Remember, this is but one tool in your container management arsenal, and as always, it’s best to understand how it works before you start using it.

More useful commands: https://github.com/PBujakiewicz/kubectl-oc-cheat-sheet

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