1# runc
2
3[](https://goreportcard.com/report/github.com/opencontainers/runc)
4[](https://pkg.go.dev/github.com/opencontainers/runc)
5[](https://bestpractices.coreinfrastructure.org/projects/588)
6[](https://github.com/opencontainers/runc/actions?query=workflow%3Avalidate)
7[](https://github.com/opencontainers/runc/actions?query=workflow%3Aci)
8[](https://cirrus-ci.com/github/opencontainers/runc)
9
10## Introduction
11
12`runc` is a CLI tool for spawning and running containers on Linux according to the OCI specification.
13
14## Releases
15
16You can find official releases of `runc` on the [release](https://github.com/opencontainers/runc/releases) page.
17
18All releases are signed by one of the keys listed in the [`runc.keyring` file in the root of this repository](runc.keyring).
19
20## Security
21
22The reporting process and disclosure communications are outlined [here](https://github.com/opencontainers/org/blob/master/SECURITY.md).
23
24### Security Audit
25A third party security audit was performed by Cure53, you can see the full report [here](https://github.com/opencontainers/runc/blob/master/docs/Security-Audit.pdf).
26
27## Building
28
29`runc` only supports Linux. It must be built with Go version 1.17 or higher.
30
31In order to enable seccomp support you will need to install `libseccomp` on your platform.
32> e.g. `libseccomp-devel` for CentOS, or `libseccomp-dev` for Ubuntu
33
34```bash
35# create a 'github.com/opencontainers' in your GOPATH/src
36cd github.com/opencontainers
37git clone https://github.com/opencontainers/runc
38cd runc
39
40make
41sudo make install
42```
43
44You can also use `go get` to install to your `GOPATH`, assuming that you have a `github.com` parent folder already created under `src`:
45
46```bash
47go get github.com/opencontainers/runc
48cd $GOPATH/src/github.com/opencontainers/runc
49make
50sudo make install
51```
52
53`runc` will be installed to `/usr/local/sbin/runc` on your system.
54
55
56#### Build Tags
57
58`runc` supports optional build tags for compiling support of various features,
59with some of them enabled by default (see `BUILDTAGS` in top-level `Makefile`).
60
61To change build tags from the default, set the `BUILDTAGS` variable for make,
62e.g. to disable seccomp:
63
64```bash
65make BUILDTAGS=""
66```
67
68| Build Tag | Feature | Enabled by default | Dependency |
69|-----------|------------------------------------|--------------------|------------|
70| seccomp | Syscall filtering | yes | libseccomp |
71
72The following build tags were used earlier, but are now obsoleted:
73 - **nokmem** (since runc v1.0.0-rc94 kernel memory settings are ignored)
74 - **apparmor** (since runc v1.0.0-rc93 the feature is always enabled)
75 - **selinux** (since runc v1.0.0-rc93 the feature is always enabled)
76
77### Running the test suite
78
79`runc` currently supports running its test suite via Docker.
80To run the suite just type `make test`.
81
82```bash
83make test
84```
85
86There 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.
87
88You can run a specific test case by setting the `TESTFLAGS` variable.
89
90```bash
91# make test TESTFLAGS="-run=SomeTestFunction"
92```
93
94You can run a specific integration test by setting the `TESTPATH` variable.
95
96```bash
97# make test TESTPATH="/checkpoint.bats"
98```
99
100You can run a specific rootless integration test by setting the `ROOTLESS_TESTPATH` variable.
101
102```bash
103# make test ROOTLESS_TESTPATH="/checkpoint.bats"
104```
105
106You can run a test using your container engine's flags by setting `CONTAINER_ENGINE_BUILD_FLAGS` and `CONTAINER_ENGINE_RUN_FLAGS` variables.
107
108```bash
109# make test CONTAINER_ENGINE_BUILD_FLAGS="--build-arg http_proxy=http://yourproxy/" CONTAINER_ENGINE_RUN_FLAGS="-e http_proxy=http://yourproxy/"
110```
111
112### Dependencies Management
113
114`runc` uses [Go Modules](https://github.com/golang/go/wiki/Modules) for dependencies management.
115Please refer to [Go Modules](https://github.com/golang/go/wiki/Modules) for how to add or update
116new dependencies.
117
118```
119# Update vendored dependencies
120make vendor
121# Verify all dependencies
122make verify-dependencies
123```
124
125## Using runc
126
127Please note that runc is a low level tool not designed with an end user
128in mind. It is mostly employed by other higher level container software.
129
130Therefore, unless there is some specific use case that prevents the use
131of tools like Docker or Podman, it is not recommended to use runc directly.
132
133If you still want to use runc, here's how.
134
135### Creating an OCI Bundle
136
137In order to use runc you must have your container in the format of an OCI bundle.
138If you have Docker installed you can use its `export` method to acquire a root filesystem from an existing Docker container.
139
140```bash
141# create the top most bundle directory
142mkdir /mycontainer
143cd /mycontainer
144
145# create the rootfs directory
146mkdir rootfs
147
148# export busybox via Docker into the rootfs directory
149docker export $(docker create busybox) | tar -C rootfs -xvf -
150```
151
152After a root filesystem is populated you just generate a spec in the format of a `config.json` file inside your bundle.
153`runc` provides a `spec` command to generate a base template spec that you are then able to edit.
154To find features and documentation for fields in the spec please refer to the [specs](https://github.com/opencontainers/runtime-spec) repository.
155
156```bash
157runc spec
158```
159
160### Running Containers
161
162Assuming you have an OCI bundle from the previous step you can execute the container in two different ways.
163
164The first way is to use the convenience command `run` that will handle creating, starting, and deleting the container after it exits.
165
166```bash
167# run as root
168cd /mycontainer
169runc run mycontainerid
170```
171
172If you used the unmodified `runc spec` template this should give you a `sh` session inside the container.
173
174The second way to start a container is using the specs lifecycle operations.
175This gives you more power over how the container is created and managed while it is running.
176This will also launch the container in the background so you will have to edit
177the `config.json` to remove the `terminal` setting for the simple examples
178below (see more details about [runc terminal handling](docs/terminals.md)).
179Your process field in the `config.json` should look like this below with `"terminal": false` and `"args": ["sleep", "5"]`.
180
181
182```json
183 "process": {
184 "terminal": false,
185 "user": {
186 "uid": 0,
187 "gid": 0
188 },
189 "args": [
190 "sleep", "5"
191 ],
192 "env": [
193 "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
194 "TERM=xterm"
195 ],
196 "cwd": "/",
197 "capabilities": {
198 "bounding": [
199 "CAP_AUDIT_WRITE",
200 "CAP_KILL",
201 "CAP_NET_BIND_SERVICE"
202 ],
203 "effective": [
204 "CAP_AUDIT_WRITE",
205 "CAP_KILL",
206 "CAP_NET_BIND_SERVICE"
207 ],
208 "inheritable": [
209 "CAP_AUDIT_WRITE",
210 "CAP_KILL",
211 "CAP_NET_BIND_SERVICE"
212 ],
213 "permitted": [
214 "CAP_AUDIT_WRITE",
215 "CAP_KILL",
216 "CAP_NET_BIND_SERVICE"
217 ],
218 "ambient": [
219 "CAP_AUDIT_WRITE",
220 "CAP_KILL",
221 "CAP_NET_BIND_SERVICE"
222 ]
223 },
224 "rlimits": [
225 {
226 "type": "RLIMIT_NOFILE",
227 "hard": 1024,
228 "soft": 1024
229 }
230 ],
231 "noNewPrivileges": true
232 },
233```
234
235Now we can go through the lifecycle operations in your shell.
236
237
238```bash
239# run as root
240cd /mycontainer
241runc create mycontainerid
242
243# view the container is created and in the "created" state
244runc list
245
246# start the process inside the container
247runc start mycontainerid
248
249# after 5 seconds view that the container has exited and is now in the stopped state
250runc list
251
252# now delete the container
253runc delete mycontainerid
254```
255
256This 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`.
257
258#### Rootless containers
259`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.
260
261**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:
262- Confirm `CONFIG_USER_NS=y` is set in your kernel configuration (normally found in `/proc/config.gz`)
263- Arch/Debian: `echo 1 > /proc/sys/kernel/unprivileged_userns_clone`
264- RHEL/CentOS 7: `echo 28633 > /proc/sys/user/max_user_namespaces`
265
266Run the following commands as an ordinary user:
267```bash
268# Same as the first example
269mkdir ~/mycontainer
270cd ~/mycontainer
271mkdir rootfs
272docker export $(docker create busybox) | tar -C rootfs -xvf -
273
274# 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.
275runc spec --rootless
276
277# The --root parameter tells runc where to store the container state. It must be writable by the user.
278runc --root /tmp/runc run mycontainerid
279```
280
281#### Supervisors
282
283`runc` can be used with process supervisors and init systems to ensure that containers are restarted when they exit.
284An example systemd unit file looks something like this.
285
286```systemd
287[Unit]
288Description=Start My Container
289
290[Service]
291Type=forking
292ExecStart=/usr/local/sbin/runc run -d --pid-file /run/mycontainerid.pid mycontainerid
293ExecStopPost=/usr/local/sbin/runc delete mycontainerid
294WorkingDirectory=/mycontainer
295PIDFile=/run/mycontainerid.pid
296
297[Install]
298WantedBy=multi-user.target
299```
300
301## More documentation
302
303* [cgroup v2](./docs/cgroup-v2.md)
304* [Checkpoint and restore](./docs/checkpoint-restore.md)
305* [systemd cgroup driver](./docs/systemd.md)
306* [Terminals and standard IO](./docs/terminals.md)
307* [Experimental features](./docs/experimental.md)
308
309## License
310
311The code and docs are released under the [Apache 2.0 license](LICENSE).
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