runc

Introduction

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

Releases

You can find official releases ofrunc on therelease page.

All releases are signed by one of the keys listed in therunc.keyring file in the root of this repository.

Security

The reporting process and disclosure communications are outlinedhere.

Security Audit

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

Building

runc only supports Linux. See the header ofgo.mod for the required Go version.

Pre-Requisites

Utilities and Libraries

In addition to Go, buildingrunc requires multiple utilities and libraries to be installed on your system.

On Ubuntu/Debian, you can install the required dependencies with:

apt update && apt install -y make gcc linux-libc-dev libseccomp-dev pkg-config git

On CentOS/Fedora, you can install the required dependencies with:

yum install -y make gcc kernel-headers libseccomp-devel pkg-config git

On Alpine Linux, you can install the required dependencies with:

apk --update add bash make gcc libseccomp-dev musl-dev linux-headers git

The following dependencies are optional:

• libseccomp - only required if you enable seccomp support; to disable, seeBuild Tags

Build

# create a 'github.com/opencontainers' in your GOPATH/srccd github.com/opencontainersgit clone https://github.com/opencontainers/runccd runcmakesudo make install

You can also usego get to install to yourGOPATH, assuming that you have agithub.com parent folder already created undersrc:

go get github.com/opencontainers/runccd $GOPATH/src/github.com/opencontainers/runcmakesudo make install

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

Version string customization

You can see the runc version by runningrunc --version. You can append a custom string to theversion using theEXTRA_VERSION make variable when building, e.g.:

make EXTRA_VERSION="+build-1"

Bear in mind to include some separator for readability.

Build Tags

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

To change build tags from the default, set theBUILDTAGS variable for make,e.g. to disable seccomp:

make BUILDTAGS=""

To add some more build tags to the default set, use theEXTRA_BUILDTAGSmake variable, e.g. to disable checkpoint/restore:

make EXTRA_BUILDTAGS="runc_nocriu"

The following build tags were used earlier, but are now obsoleted:

• runc_nodmz (since runc v1.2.1 runc dmz binary is dropped)
• nokmem (since runc v1.0.0-rc94 kernel memory settings are ignored)
• apparmor (since runc v1.0.0-rc93 the feature is always enabled)
• selinux (since runc v1.0.0-rc93 the feature is always enabled)

Running the test suite

runc currently supports running its test suite via Docker.To run the suite just typemake 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 theTESTFLAGS variable.

# make test TESTFLAGS="-run=SomeTestFunction"

You can run a specific integration test by setting theTESTPATH variable.

# make test TESTPATH="/checkpoint.bats"

You can run a specific rootless integration test by setting theROOTLESS_TESTPATH variable.

# make test ROOTLESS_TESTPATH="/checkpoint.bats"

You can run a test using your container engine's flags by settingCONTAINER_ENGINE_BUILD_FLAGS andCONTAINER_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/"

Go Dependencies Management

runc usesGo Modules for dependencies management.Please refer toGo Modules for how to add or updatenew dependencies.

# Update vendored dependenciesmake vendor# Verify all dependenciesmake verify-dependencies

Using runc

Please note that runc is a low level tool not designed with an end userin mind. It is mostly employed by other higher level container software.

Therefore, unless there is some specific use case that prevents the useof tools like Docker or Podman, it is not recommended to use runc directly.

If you still want to use runc, here's how.

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 itsexport method to acquire a root filesystem from an existing Docker container.

# create the top most bundle directorymkdir /mycontainercd /mycontainer# create the rootfs directorymkdir rootfs# export busybox via Docker into the rootfs directorydocker export $(docker create busybox) | tar -C rootfs -xvf -

After a root filesystem is populated you just generate a spec in the format of aconfig.json file inside your bundle.runc provides aspec 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 thespecs 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 commandrun that will handle creating, starting, and deleting the container after it exits.

# run as rootcd /mycontainerrunc run mycontainerid

If you used the unmodifiedrunc spec template this should give you ash 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 edittheconfig.json to remove theterminal setting for the simple examplesbelow (see more details aboutrunc terminal handling).Your process field in theconfig.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 rootcd /mycontainerrunc create mycontainerid# view the container is created and in the "created" staterunc list# start the process inside the containerrunc start mycontainerid# after 5 seconds view that the container has exited and is now in the stopped staterunc list# now delete the containerrunc 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 aftercreate but beforestart.

Rootless containers

runc has the ability to run containers without root privileges. This is calledrootless. You need to pass some parameters torunc 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:

• ConfirmCONFIG_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:

# Same as the first examplemkdir ~/mycontainercd ~/mycontainermkdir rootfsdocker 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=forkingExecStart=/usr/local/sbin/runc run -d --pid-file /run/mycontainerid.pid mycontaineridExecStopPost=/usr/local/sbin/runc delete mycontaineridWorkingDirectory=/mycontainerPIDFile=/run/mycontainerid.pid[Install]WantedBy=multi-user.target

More documentation

• Spec conformance
• cgroup v2
• Checkpoint and restore
• systemd cgroup driver
• Terminals and standard IO
• Experimental features

License

The code and docs are released under theApache 2.0 license.

There is no documentation for this package.