Alexander Larsson
ca9544522e
We use a unix domain socketpair instead of a pipe for the sync pipe, which allows us to use two-way shutdown. After sending the context we shut down the write side which lets the child know it finished reading. We then block on a read in the parent for the child closing the file (ensuring we close our version of it too) to sync for when the child is finished initializing. If the read is non-empty we assume this is an error report and fail with an error. Otherwise we continue as before. This also means we're now calling back the start callback later, meaning at that point its more likely to have succeeded, as well as having consumed all the container resources (like volume mounts, making it safe to e.g. unmount them when the start callback is called). Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
libcontainer - reference implementation for containers
Note on API changes:
Please bear with us while we work on making the libcontainer API stable and something that we can support long term. We are currently discussing the API with the community, therefore, if you currently depend on libcontainer please pin your dependency at a specific tag or commit id. Please join the discussion and help shape the API.
Background
libcontainer specifies configuration options for what a container is. It provides a native Go implementation for using Linux namespaces with no external dependencies. libcontainer provides many convenience functions for working with namespaces, networking, and management.
Container
A container is a self contained execution environment that shares the kernel of the host system and which is (optionally) isolated from other containers in the system.
libcontainer may be used to execute a process in a container. If a user tries to run a new process inside an existing container, the new process is added to the processes executing in the container.
Root file system
A container runs with a directory known as its root file system, or rootfs, mounted as the file system root. The rootfs is usually a full system tree.
Configuration
A container is initially configured by supplying configuration data when the container is created.
nsinit
nsinit is a cli application which demonstrates the use of libcontainer. It is able to spawn new containers or join existing containers, based on the current directory.
To use nsinit, cd into a Linux rootfs and copy a container.json file into the directory with your specified configuration. Environment, networking, and different capabilities for the container are specified in this file. The configuration is used for each process executed inside the container.
See the sample_configs folder for examples of what the container configuration should look like.
To execute /bin/bash in the current directory as a container just run the following as root:
nsinit exec /bin/bash
If you wish to spawn another process inside the container while your current bash session is running, run the same command again to get another bash shell (or change the command). If the original process (PID 1) dies, all other processes spawned inside the container will be killed and the namespace will be removed.
You can identify if a process is running in a container by looking to see if state.json is in the root of the directory.
You may also specify an alternate root place where the container.json file is read and where the state.json file will be saved.
Future
See the roadmap.
Copyright and license
Code and documentation copyright 2014 Docker, inc. Code released under the Apache 2.0 license. Docs released under Creative commons.
Hacking on libcontainer
First of all, please familiarise yourself with the libcontainer Principles.
If you're a contributor or aspiring contributor, you should read the Contributors' Guide.
If you're a maintainer or aspiring maintainer, you should read the Maintainers' Guide and "How can I become a maintainer?" in the Contributors' Guide.