200 lines
6.6 KiB
Markdown
200 lines
6.6 KiB
Markdown
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# runc
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[](https://travis-ci.org/opencontainers/runc)
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[](https://goreportcard.com/report/github.com/opencontainers/runc)
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## Introduction
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`runc` is a CLI tool for spawning and running containers according to the OCI specification.
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## Releases
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`runc` depends on and tracks the [runtime-spec](https://github.com/opencontainers/runtime-spec) repository.
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We will try to make sure that `runc` and the OCI specification major versions stay in lockstep.
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This means that `runc` 1.0.0 should implement the 1.0 version of the specification.
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You can find official releases of `runc` on the [release](https://github.com/opencontainers/runc/releases) page.
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### Security
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If you wish to report a security issue, please disclose the issue responsibly
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to security@opencontainers.org.
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## Building
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`runc` currently supports the Linux platform with various architecture support.
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It must be built with Go version 1.6 or higher in order for some features to function properly.
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In order to enable seccomp support you will need to install `libseccomp` on your platform.
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> e.g. `libseccomp-devel` for CentOS, or `libseccomp-dev` for Ubuntu
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Otherwise, if you do not want to build `runc` with seccomp support you can add `BUILDTAGS=""` when running make.
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```bash
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# create a 'github.com/opencontainers' in your GOPATH/src
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cd github.com/opencontainers
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git clone https://github.com/opencontainers/runc
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cd runc
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make
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sudo make install
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```
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`runc` will be installed to `/usr/local/sbin/runc` on your system.
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#### Build Tags
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`runc` supports optional build tags for compiling support of various features.
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To add build tags to the make option the `BUILDTAGS` variable must be set.
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```bash
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make BUILDTAGS='seccomp apparmor'
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```
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| Build Tag | Feature | Dependency |
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|-----------|------------------------------------|-------------|
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| seccomp | Syscall filtering | libseccomp |
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| selinux | selinux process and mount labeling | <none> |
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| apparmor | apparmor profile support | libapparmor |
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| ambient | ambient capability support | kernel 4.3 |
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### Running the test suite
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`runc` currently supports running its test suite via Docker.
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To run the suite just type `make test`.
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```bash
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make test
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```
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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.
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You can run a specific test case by setting the `TESTFLAGS` variable.
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```bash
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# make test TESTFLAGS="-run=SomeTestFunction"
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```
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## Using runc
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### Creating an OCI Bundle
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In order to use runc you must have your container in the format of an OCI bundle.
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If you have Docker installed you can use its `export` method to acquire a root filesystem from an existing Docker container.
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```bash
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# create the top most bundle directory
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mkdir /mycontainer
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cd /mycontainer
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# create the rootfs directory
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mkdir rootfs
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# export busybox via Docker into the rootfs directory
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docker export $(docker create busybox) | tar -C rootfs -xvf -
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```
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After a root filesystem is populated you just generate a spec in the format of a `config.json` file inside your bundle.
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`runc` provides a `spec` command to generate a base template spec that you are then able to edit.
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To find features and documentation for fields in the spec please refer to the [specs](https://github.com/opencontainers/runtime-spec) repository.
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```bash
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runc spec
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```
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### Running Containers
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Assuming you have an OCI bundle from the previous step you can execute the container in two different ways.
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The first way is to use the convenience command `run` that will handle creating, starting, and deleting the container after it exits.
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```bash
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cd /mycontainer
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runc run mycontainerid
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```
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If you used the unmodified `runc spec` template this should give you a `sh` session inside the container.
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The second way to start a container is using the specs lifecycle operations.
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This gives you more power over how the container is created and managed while it is running.
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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.
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Your process field in the `config.json` should look like this below with `"terminal": false` and `"args": ["sleep", "5"]`.
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```json
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"process": {
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"terminal": false,
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"user": {
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"uid": 0,
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"gid": 0
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},
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"args": [
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"sleep", "5"
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],
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"env": [
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"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
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"TERM=xterm"
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],
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"cwd": "/",
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"capabilities": [
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"CAP_AUDIT_WRITE",
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"CAP_KILL",
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"CAP_NET_BIND_SERVICE"
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],
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"rlimits": [
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{
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"type": "RLIMIT_NOFILE",
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"hard": 1024,
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"soft": 1024
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}
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],
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"noNewPrivileges": true
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},
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```
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Now we can go though the lifecycle operations in your shell.
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```bash
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cd /mycontainer
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runc create mycontainerid
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# view the container is created and in the "created" state
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runc list
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# start the process inside the container
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runc start mycontainerid
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# after 5 seconds view that the container has exited and is now in the stopped state
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runc list
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# now delete the container
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runc delete mycontainerid
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```
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This adds more complexity but allows higher level systems to manage runc and provides points in the containers creation to setup various settings after the container has created and/or before it is deleted.
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This is commonly used to setup the container's network stack after `create` but before `start` where the user's defined process will be running.
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#### Supervisors
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`runc` can be used with process supervisors and init systems to ensure that containers are restarted when they exit.
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An example systemd unit file looks something like this.
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```systemd
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[Unit]
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Description=Start My Container
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[Service]
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Type=forking
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ExecStart=/usr/local/sbin/runc run -d --pid-file /run/mycontainerid.pid mycontainerid
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ExecStopPost=/usr/local/sbin/runc delete mycontainerid
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WorkingDirectory=/mycontainer
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PIDFile=/run/mycontainerid.pid
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[Install]
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WantedBy=multi-user.target
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```
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