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 of runc on the release page.
All releases are signed by one of the keys listed in the runc.keyring file in the root of this repository.
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 only supports Linux. See the header of go.mod for the minimally required Go version.
Pre-Requisites
Utilities and Libraries
In addition to Go, building runc 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, see Build Tags.libpathrs - only required if you enable libpathrs support; to disable, see Build Tags.
For notes on installing libpathrs, see the next section.
libpathrs
libpathrs is a Rust library runc can optionally use for path safety. As
mentioned in the build tag section, its use is controlled with
the libpathrs build tag. runc currently requires at least libpathrs 0.2.5
in order to function properly.
At time of writing, very few distributions have libpathrs packages and so it is
usually necessary to build and install it locally. For detailed installation
instructions, see the upstream documentation, but for
development builds the following instructions should be sufficient:
libpathrs requires Rust 1.63+ (which is available on almost any distribution,
including Debian oldstable and enterprise distributions like RHEL or SLES).
Assuming you already have cargo installed (as well as other libpathrs
dependencies like clang and lld), the following steps are all that are
really necessary to install libpathrs:
LIBPATHRS_VERSION=0.2.5
curl -o - -sSL https://github.com/cyphar/libpathrs/releases/download/v${LIBPATHRS_VERSION}/libpathrs-${LIBPATHRS_VERSION}.tar.xz | tar xvfJ -
cd libpathrs-${LIBPATHRS_VERSION}/
make release
sudo ./install.sh --prefix=/usr/local
sudo ldconfig
As part of our CI, we make use of a custom installation script for
libpathrs which may be useful as a reference for
folks with more complicated needs. With script/build-libpathrs.sh the
installation of libpathrs becomes as simple as:
sudo ./script/build-libpathrs.sh "$LIBPATHRS_VERSION" /usr/local
sudo ldconfig
However, please note that this installation script is completely
unsupported and is not really intended for general use (it includes some
workarounds for issues in our CI which will no longer be necessary once
libpathrs has distribution packages we can use).
Build
# 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.
Version string customization
You can see the runc version by running runc --version. You can append a custom string to the
version using the EXTRA_VERSION make variable when building, e.g.:
make EXTRA_VERSION="+build-1"
Bear in mind to include some separator for readability.
runc supports optional build tags for compiling support of various features,
with some of them enabled by default in the top-level Makefile.
The following build tags are currently recognized:
| Build Tag |
Feature |
Set by Default |
Dependencies |
seccomp |
Syscall filtering using libseccomp. |
yes |
libseccomp |
libpathrs |
Use libpathrs for path safety. |
yes |
libpathrs |
runc_nocriu |
Disables runc checkpoint/restore. |
no |
criu |
To add or remove build tags from the default set, use the RUNC_BUILDTAGS
make or shell variable. Tags prefixed with - are removed from the default set;
others are added. For example:
# Add runc_nocriu and remove seccomp tag.
make RUNC_BUILDTAGS="runc_nocriu -seccomp"
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 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/"
Go Dependencies Management
runc uses Go Modules for dependencies management.
Please refer to Go Modules for how to add or update
new dependencies.
# Update vendored dependencies
make vendor
# Verify all dependencies
make verify-dependencies
Using runc
Please note that runc is a low level tool not designed with an end user
in mind. It is mostly employed by other higher level container software.
Therefore, unless there is some specific use case that prevents the use
of 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 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
below (see more details about runc terminal handling).
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:
# 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
More documentation
License
The code and docs are released under the Apache 2.0 license.
runc 是一个命令行工具,用于在 Linux 上按照 OCI(开放容器倡议)规范创建和运行容器。