minit

---

minimal subreaper init for containers

📝 Table of Contents

• About
• Getting Started
• Running the tests
• Usage
• TODO
• Contributing

🧐 About

Minit acts as a init process for your application. It does:

• spawn a child process to run your application
• forward signals to child processes
• adopt orphaned processes
• reaps terminated child processes to prevent zombie processes

What's the difference between minit and tini?

Functionality	tini	minit
forward signals	✅	✅
adopt orphaned processes	✅	✅
reap zombie processes	✅	✅
wait for all processes	❌	✅

Even if you start tini with the -s flag or the TINI_SUBREAPER environment variable set, it won't wait for the all adopted child processes if the spawned application exits. That means if your application A forks/spawns process B and C, then exits before they finish, tini will also finish and still leave process B and C as zombie processes behind.

Why would I ever want to adopt all orphaned processes and prevent zombies?

Let's skip the lecture about not running daemons within containers, best practices of fork/wait pairing or even signaling child processes when the parent dies. At the end of the day, an application wants a clean exit. This includes its child processes. An abrupt termination of them can result in unwanted behaviour, such as state corruption or misleading status.

🏁 Getting Started

You can build the application using make minit. You can also build the sample application using make sample, which simply forks a sleep system command and exits, allowing a quick test.

Prerequisites

The repository contains a developer container that is usable with the VSCode [Remote - Containers][ms-vscode-remote.remote-containers] extension. Due to this extension lack of support for buildkit, the container build must be done through a task, which is also provided.

If you're on Linux and want to develop directly, then install:

• GNU Make
• GCC
• Linux headers
• libc-dev or equivalent package
• procps-dev or equivalent package

Installing

Release versions are built statically, which means you can use minit on a scratch container. In fact the release container is based on scratch, with only the binary. You can base off it, or just copy the binary from the image:

FROM minit:latest AS minit

FROM scratch

COPY --from=minit /usr/local/bin/minit /usr/local/bin/minit

# your awesome directives go here

ENTRYPOINT ["minit", "<your-app>"]
CMD ["minit", "<your-app>"]

🔧 Running the tests

The binary is only tested for memory leaks, using valgrind. This is available as the test target on the main Dockerfile, and can be executed using make test.

The final container image be tested for its structure using make image-test.

🎈 Usage

Prefix any executable with minit. It takes any arguments, which will all be used as-is to execute from the spawned process. For instance, if you want to run sleep 10 with minit, use:

minit sleep 10

That's it.