Doker Conventions

Exit Codes

A DockerShim process will return one of the following exit codes:

  • 0 - If the application logic returns without exception.
  • 64 - If the application logic directly threw an unhandled exception. Unhandled exceptions are logged before the process exits.
  • 65 - If the application logic indirectly threw an unhandled exception (e.g., from a thread pool thread). Unhandled exceptions are logged before the process exits.
  • 66 - If the application logic was requested to shutdown, but did not do so within the exit timeout (see DockerShimSettings.ExitTimeout).
  • (other) - If the application logic returns an int, then that value is used as the process exit code.

Exit codes are returned by DockerShim even if you use static void Main as your entrypoint.


DockerShim responds to Ctrl-C (if your container is run interactively) as well as docker stop on all platforms and container types. Note that for docker stop to work with Windows containers, they must have a base image and host running Windows Version 1709 or higher.

Signal Specifics

DockerShim listens to various signals based on OS:

  • Other: SIGINT and SIGTERM

These are all treated the same: as a graceful stop request. When one of these signals is received, the DockerShimContext.ExitRequested cancellation token is cancelled. When this token is cancelled, your code should stop taking on new work. It should complete the work it already has and then exit.

When a signal comes in, DockerShim will start a kill timer (see DockerShimSettings.ExitTimeout). If the application code has not returned within that timeout, DockerShim will exit the process with exit code 66.


Docker expects logs to be written to stdout (or stderr), with one line per log message.

DockerShim has a core logging factory, exposed at DockerShimContext.LoggingFactory. All of DockerShim’s logs go through this factory (using the "DockerShim" category/logger name), and this same factory can be used to create application logs.

By default, all log messages sent to DockerShimContext.LoggingFactory are formatted on a single line using backslash-escaping. These lines are then written to stdout.

Redirecting DockerShim Logs

Docker applications that do their own application logging directly will want to redirect DockerShim’s logging. This is done by setting DockerShimSettings.LoggingFactory before calling into DockerShimRunner.Main. DockerShim will then use the provided ILoggerFactory instead of its own factory and provider.

static void Main(string[] args)
  var myLoggerFactory = new LoggerFactory();
  myLoggerFactory.AddMyOwnProvider(); // log4net, seq, gelf, whatever...

  var settings = new DockerShimSettings
    MaximumRuntime = TimeSpan.FromHours(2),
    LoggerFactory = myLoggerFactory,
  DockerShimRunner.Main(settings, context =>
    var loggerFactory = context.LoggerFactory; // Same instance as `myLoggerFactory` that we passed into the settings.

This way you can send DockerShim’s own logs to your customized logging provider instead of as stdout to Docker.