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moby--moby/docs/rootless.md

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Rootless mode (Experimental)

The rootless mode allows running dockerd as an unprivileged user, using user_namespaces(7), mount_namespaces(7), network_namespaces(7).

No SETUID/SETCAP binary is required except newuidmap and newgidmap.

Requirements

  • newuidmap and newgidmap need to be installed on the host. These commands are provided by the uidmap package on most distros.

  • /etc/subuid and /etc/subgid should contain >= 65536 sub-IDs. e.g. penguin:231072:65536.

$ id -u
1001
$ whoami
penguin
$ grep ^$(whoami): /etc/subuid
penguin:231072:65536
$ grep ^$(whoami): /etc/subgid
penguin:231072:65536
  • Either slirp4netns (v0.3+) or VPNKit needs to be installed. slirp4netns is preferred for the best performance.

Distribution-specific hint

Debian (excluding Ubuntu)

  • sudo sh -c "echo 1 > /proc/sys/kernel/unprivileged_userns_clone" is required

Arch Linux

  • sudo sh -c "echo 1 > /proc/sys/kernel/unprivileged_userns_clone" is required

openSUSE

  • sudo modprobe ip_tables iptable_mangle iptable_nat iptable_filter is required. (This is likely to be required on other distros as well)

RHEL/CentOS 7

Restrictions

  • Only vfs graphdriver is supported. However, on Ubuntu and a few distros, overlay2 and overlay are also supported.
  • Following features are not supported:
    • Cgroups (including docker top, which depends on the cgroups device controller)
    • Apparmor
    • Checkpoint
    • Overlay network

Usage

Daemon

You need to run dockerd-rootless.sh instead of dockerd.

$ dockerd-rootless.sh --experimental"

As Rootless mode is experimental per se, currently you always need to run dockerd-rootless.sh with --experimental.

Remarks:

  • The socket path is set to $XDG_RUNTIME_DIR/docker.sock by default. $XDG_RUNTIME_DIR is typically set to /run/user/$UID.
  • The data dir is set to ~/.local/share/docker by default.
  • The exec dir is set to $XDG_RUNTIME_DIR/docker by default.
  • The daemon config dir is set to ~/.config/docker (not ~/.docker, which is used by the client) by default.
  • The dockerd-rootless.sh script executes dockerd in its own user, mount, and network namespaces. You can enter the namespaces by running nsenter -U --preserve-credentials -n -m -t $(cat $XDG_RUNTIME_DIR/docker.pid).

Client

You can just use the upstream Docker client but you need to set the socket path explicitly.

$ docker -H unix://$XDG_RUNTIME_DIR/docker.sock run -d nginx

Exposing ports

In addition to exposing container ports to the dockerd network namespace, you also need to expose the ports in the dockerd network namespace to the host network namespace.

$ docker -H unix://$XDG_RUNTIME_DIR/docker.sock run -d -p 80:80 nginx
$ socat -t -- TCP-LISTEN:8080,reuseaddr,fork EXEC:"nsenter -U -n -t $(cat $XDG_RUNTIME_DIR/docker.pid) socat -t -- STDIN TCP4\:127.0.0.1\:80"

In future, dockerd will be able to expose the ports automatically.

Routing ping packets

To route ping packets, you need to set up net.ipv4.ping_group_range properly as the root.

$ sudo sh -c "echo 0   2147483647  > /proc/sys/net/ipv4/ping_group_range"