Rootless Containers
Docker/Moby
Rootless Docker/Moby was implemented in 2018 following rootless runc, containerd, and BuildKit. Rootless Docker has been merged to the Docker/Moby upstream since Docker 19.03.
Docker 19.03 provides almost full features for Rootless mode, including support
for port fowarding (docker run -p) and multi-container networking (docker network create),
but it doesn’t support limiting resources with cgroup.
Docker 20.10 added support for limiting resources using cgroup v2.
Note
Please read the common steps first.
Especially, make sure
$XDG_RUNTIME_DIRto be set properly.
Docker (since 20.10) provides docker-ce-rootless-extras RPMs and DEBs that can be installed by the root for all the users on the host.
The package is usually automatically installed on installing Docker from https://get.docker.com.
$ curl -o install.sh -fsSL https://get.docker.com
$ sudo sh install.sh
After installing Docker, run the following command as a non-root user to create the systemd user-instance unit:
$ dockerd-rootless-setuptool.sh install
This method does not use RPMs/DEBS and can be executed by a non-root user without sudo.
$ curl -o rootless-install.sh -fsSL https://get.docker.com/rootless
$ sh rootless-install.sh
$ export PATH=$HOME/bin:$PATH
For backward compatibility, the docker CLI attempts to connect to the rootful daemon by default.
To connect to the rootless daemon, you need to set either the CLI context or an environment variable.
$ docker context use rootless
$ docker run hello-world
$ export DOCKER_HOST=unix://$XDG_RUNTIME_DIR/docker.sock
$ docker run hello-world
To start/stop the daemon, use systemctl --user <start|stop> docker instead of systemctl <start|stop> docker.
The systemd unit file is located as ~/.config/systemd/user/docker.service.
Resource-related flags of docker run, such as --cpus, --memory, --blkio-weight, and --pids-limit can be used only when the following conditions are satisfied:
- Docker/Moby version is 20.10 or later
- containerd version is 1.4 or later
- runc version is 1.0-rc91 or later
- The host is running with cgroup v2
- The host is running with systemd
To impose resource limitations without cgroup, see https://docs.docker.com/engine/security/rootless/#limiting-resources
Docker/Moby uses slirp4netns as the default network stack if slirp4netns v0.4.0 or later is installed. Otherwise it falls back to VPNKit.
slirp4netns is usually automatically installed on installing the docker-ce-rootless-extras package.
If slirp4netns is not automatically installed, run sudo apt-get install slirp4netns, sudo dnf install slirp4netns, or download the official slirp4netns binary
to ~/bin so that Docker/Moby can pick it up automatically. The functionalities are same as VPNKit, but slirp4netns is known to have better throughput.
Docker/Moby also supports lxc-user-nic SETUID binary experimentally: https://docs.docker.com/engine/security/rootless/#changing-the-network-stack
Docker/Moby uses RootlessKit as the default port forwarder.
However, as explained in How it works, sometimes slirp4netns port forwarder is preferred over RootlessKit port forwarder.
To change the port forwarder to slirp4netns, create ~/.config/systemd/user/docker.service.d/override.conf with the following content:
[Service]
Environment="DOCKERD_ROOTLESS_ROOTLESSKIT_PORT_DRIVER=slirp4netns"
And then restart the daemon:
$ systemctl --user daemon-reload
$ systemctl --user restart docker
You need to run sudo loginctl enable-linger .... See Getting Started/Login.
Run the following commands to remove all containers and configurations:
$ dockerd-rootless-setuptool.sh uninstall
$ ~/bin/rootlesskit rm -rf ~/.local/share/docker ~/.config/docker
To uninstall binaries, run sudo apt-get remove docker-ce-*
or sudo dnf remove docker-ce-*.
If you installed Rootless Docker without using packages,
remove the following files under ~/bin:
containerd
containerd-shim
containerd-shim-runc-v2
ctr
docker
docker-init
docker-proxy
dockerd
dockerd-rootless-setuptool.sh
dockerd-rootless.sh
rootlesskit
rootlesskit-docker-proxy
runc
vpnkit