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.
Security
If you wish to report a security issue, please disclose the issue responsibly
to security@opencontainers.org.
Building
runc
currently supports the Linux platform with various architecture support.
It must be built with Go version 1.6 or higher in order for some features to function properly.
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
Otherwise, if you do not want to build runc
with seccomp support you can add BUILDTAGS=""
when running make.
# 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.
runc
supports optional build tags for compiling support of various features.
To add build tags to the make option the BUILDTAGS
variable must be set.
make BUILDTAGS='seccomp apparmor'
Build Tag |
Feature |
Dependency |
seccomp |
Syscall filtering |
libseccomp |
selinux |
selinux process and mount labeling |
|
apparmor |
apparmor profile support |
|
ambient |
ambient capability support |
kernel 4.3 |
nokmem |
disable kernel memory account |
|
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 test in your proxy environment by setting DOCKER_BUILD_PROXY
and DOCKER_RUN_PROXY
variables.
# make test DOCKER_BUILD_PROXY="--build-arg HTTP_PROXY=http://yourproxy/" DOCKER_RUN_PROXY="-e HTTP_PROXY=http://yourproxy/"
Dependencies Management
runc
uses vndr for dependencies management.
Please refer to vndr for how to add or update
new 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. 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
License
The code and docs are released under the Apache 2.0 license.