runc

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.

Currently, the following features are not considered to be production-ready:

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 )

is set in your kernel configuration (normally found in ) 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:

# 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.