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opencontainers

Description

CLI tool for spawning and running containers according to the OCI specification

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runc

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Introduction

runc
is a CLI tool for spawning and running containers according to the OCI specification.

Releases

runc
depends on and tracks the runtime-spec repository. We will try to make sure that
runc
and the OCI specification major versions stay in lockstep. This means that
runc
1.0.0 should implement the 1.0 version of the specification.

You can find official releases of

runc
on the release page.

Security

The reporting process and disclosure communications are outlined here.

Security Audit

A third party security audit was performed by Cure53, you can see the full report here.

Building

runc
currently supports the Linux platform with various architecture support. It must be built with Go version 1.13 or higher.

In order to enable seccomp support you will need to install

libseccomp
on your platform.

e.g.

libseccomp-devel
for CentOS, or
libseccomp-dev
for Ubuntu
# create a 'github.com/opencontainers' in your GOPATH/src
cd github.com/opencontainers
git clone https://github.com/opencontainers/runc
cd runc

make sudo make install

You can also use

go get
to install to your
GOPATH
, assuming that you have a
github.com
parent folder already created under
src
:
go get github.com/opencontainers/runc
cd $GOPATH/src/github.com/opencontainers/runc
make
sudo make install

runc
will be installed to
/usr/local/sbin/runc
on your system.

Build Tags

runc
supports optional build tags for compiling support of various features, with some of them enabled by default (see
BUILDTAGS
in top-level
Makefile
).

To change build tags from the default, set the

BUILDTAGS
variable for make, e.g.
make BUILDTAGS='seccomp apparmor'

| Build Tag | Feature | Enabled by default | Dependency | |-----------|------------------------------------|--------------------|------------| | seccomp | Syscall filtering | yes | libseccomp | | selinux | selinux process and mount labeling | yes | | | apparmor | apparmor profile support | yes | | | nokmem | disable kernel memory accounting | no | |

Running the test suite

runc
currently supports running its test suite via Docker. To run the suite just type
make test
.
make test

There are additional make targets for running the tests outside of a container but this is not recommended as the tests are written with the expectation that they can write and remove anywhere.

You can run a specific test case by setting the

TESTFLAGS
variable.
# make test TESTFLAGS="-run=SomeTestFunction"

You can run a specific integration test by setting the

TESTPATH
variable.
# make test TESTPATH="/checkpoint.bats"

You can run a specific rootless integration test by setting the

ROOTLESS_TESTPATH
variable.
# make test ROOTLESS_TESTPATH="/checkpoint.bats"

You can run a test using your container engine's flags by setting

CONTAINER_ENGINE_BUILD_FLAGS
and
CONTAINER_ENGINE_RUN_FLAGS
variables.
# make test CONTAINER_ENGINE_BUILD_FLAGS="--build-arg http_proxy=http://yourproxy/" CONTAINER_ENGINE_RUN_FLAGS="-e http_proxy=http://yourproxy/"

Dependencies Management

runc
uses Go Modules for dependencies management. Please refer to Go Modules for how to add or update new dependencies. When updating dependencies, be sure that you are running Go
1.14
or newer.
# Update vendored dependencies
make vendor
# Verify all dependencies
make verify-dependencies

Using runc

Creating an OCI Bundle

In order to use runc you must have your container in the format of an OCI bundle. If you have Docker installed you can use its

export
method to acquire a root filesystem from an existing Docker container.
# create the top most bundle directory
mkdir /mycontainer
cd /mycontainer

create the rootfs directory

mkdir rootfs

export busybox via Docker into the rootfs directory

docker export $(docker create busybox) | tar -C rootfs -xvf -

After a root filesystem is populated you just generate a spec in the format of a

config.json
file inside your bundle.
runc
provides a
spec
command to generate a base template spec that you are then able to edit. To find features and documentation for fields in the spec please refer to the specs repository.
runc spec

Running Containers

Assuming you have an OCI bundle from the previous step you can execute the container in two different ways.

The first way is to use the convenience command

run
that will handle creating, starting, and deleting the container after it exits.
# run as root
cd /mycontainer
runc run mycontainerid

If you used the unmodified

runc spec
template this should give you a
sh
session inside the container.

The second way to start a container is using the specs lifecycle operations. This gives you more power over how the container is created and managed while it is running. This will also launch the container in the background so you will have to edit the

config.json
to remove the
terminal
setting for the simple examples here. Your process field in the
config.json
should look like this below with
"terminal": false
and
"args": ["sleep", "5"]
.
        "process": {
                "terminal": false,
                "user": {
                        "uid": 0,
                        "gid": 0
                },
                "args": [
                        "sleep", "5"
                ],
                "env": [
                        "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                        "TERM=xterm"
                ],
                "cwd": "/",
                "capabilities": {
                        "bounding": [
                                "CAP_AUDIT_WRITE",
                                "CAP_KILL",
                                "CAP_NET_BIND_SERVICE"
                        ],
                        "effective": [
                                "CAP_AUDIT_WRITE",
                                "CAP_KILL",
                                "CAP_NET_BIND_SERVICE"
                        ],
                        "inheritable": [
                                "CAP_AUDIT_WRITE",
                                "CAP_KILL",
                                "CAP_NET_BIND_SERVICE"
                        ],
                        "permitted": [
                                "CAP_AUDIT_WRITE",
                                "CAP_KILL",
                                "CAP_NET_BIND_SERVICE"
                        ],
                        "ambient": [
                                "CAP_AUDIT_WRITE",
                                "CAP_KILL",
                                "CAP_NET_BIND_SERVICE"
                        ]
                },
                "rlimits": [
                        {
                                "type": "RLIMIT_NOFILE",
                                "hard": 1024,
                                "soft": 1024
                        }
                ],
                "noNewPrivileges": true
        },

Now we can go through the lifecycle operations in your shell.

# run as root
cd /mycontainer
runc create mycontainerid

view the container is created and in the "created" state

runc list

start the process inside the container

runc start mycontainerid

after 5 seconds view that the container has exited and is now in the stopped state

runc list

now delete the container

runc delete mycontainerid

This allows higher level systems to augment the containers creation logic with setup of various settings after the container is created and/or before it is deleted. For example, the container's network stack is commonly set up after

create
but before
start
.

Rootless containers

runc
has the ability to run containers without root privileges. This is called
rootless
. You need to pass some parameters to
runc
in order to run rootless containers. See below and compare with the previous version.

Note: In order to use this feature, "User Namespaces" must be compiled and enabled in your kernel. There are various ways to do this depending on your distribution: - Confirm

CONFIG_USER_NS=y
is set in your kernel configuration (normally found in
/proc/config.gz
) - Arch/Debian:
echo 1 > /proc/sys/kernel/unprivileged_userns_clone
- RHEL/CentOS 7:
echo 28633 > /proc/sys/user/max_user_namespaces

Run the following commands as an ordinary user: ```bash

Same as the first example

mkdir ~/mycontainer cd ~/mycontainer mkdir rootfs docker export $(docker create busybox) | tar -C rootfs -xvf -

The --rootless parameter instructs runc spec to generate a configuration for a rootless container, which will allow you to run the container as a non-root user.

runc spec --rootless

The --root parameter tells runc where to store the container state. It must be writable by the user.

runc --root /tmp/runc run mycontainerid ```

Supervisors

runc
can be used with process supervisors and init systems to ensure that containers are restarted when they exit. An example systemd unit file looks something like this.
[Unit]
Description=Start My Container

[Service] Type=forking ExecStart=/usr/local/sbin/runc run -d --pid-file /run/mycontainerid.pid mycontainerid ExecStopPost=/usr/local/sbin/runc delete mycontainerid WorkingDirectory=/mycontainer PIDFile=/run/mycontainerid.pid

[Install] WantedBy=multi-user.target

cgroup v2

See

./docs/cgroup-v2.md
.

License

The code and docs are released under the Apache 2.0 license.

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