containerd (nerdctl)

nerdctl is a Docker-compatible CLI for containerd.

nerdctl comes with helper scripts for running rootless containerd.

To run rootless containerd without nerdctl, see https://github.com/containerd/containerd/blob/master/docs/rootless.md

Installation

Note

Please read the common steps first.

Especially, make sure $XDG_RUNTIME_DIR to be set properly.

Download nerdctl-full-<VERSION>-linux-amd64.tar.gz from https://github.com/containerd/nerdctl/releases , and extract the archive onto /usr/local (system-wide) or ~/.local (home).

Then, run containerd-rootless-setuptool.sh install to set up the systemd unit:

$ containerd-rootless-setuptool.sh install
[INFO] Checking RootlessKit functionality
[INFO] Checking cgroup v2
[INFO] Checking overlayfs
[INFO] Requirements are satisfied
[INFO] Creating "/home/exampleuser/.config/systemd/user/containerd.service"
[INFO] Starting systemd unit "containerd.service"
+ systemctl --user start containerd.service
+ sleep 3
+ systemctl --user --no-pager --full status containerd.service
● containerd.service - containerd (Rootless)
     Loaded: loaded (/home/exampleuser/.config/systemd/user/containerd.service; disabled; vendor preset: enabled)
    Drop-In: /home/exampleuser/.config/systemd/user/containerd.service.d
             └─override.conf
     Active: active (running) since Fri 2021-04-23 16:17:57 JST; 3s ago
   Main PID: 36976 (rootlesskit)
      Tasks: 30
     Memory: 21.1M
        CPU: 165ms
     CGroup: /user.slice/user-1001.slice/user@1001.service/app.slice/containerd.service
             ├─36976 rootlesskit --state-dir=/run/user/1001/containerd-rootless --net=slirp4netns --mtu=65520 --slirp4netns-sandbox=auto --slirp4netns-seccomp=auto --disable-host-loopback --port-driver=builtin --copy-up=/etc --copy-up=/run --copy-up=/var/lib --propagation=rslave /usr/local/bin/containerd-rootless.sh
             ├─36988 /proc/self/exe --state-dir=/run/user/1001/containerd-rootless --net=slirp4netns --mtu=65520 --slirp4netns-sandbox=auto --slirp4netns-seccomp=auto --disable-host-loopback --port-driver=builtin --copy-up=/etc --copy-up=/run --copy-up=/var/lib --propagation=rslave /usr/local/bin/containerd-rootless.sh
             ├─37007 slirp4netns --mtu 65520 -r 3 --disable-host-loopback --enable-sandbox --enable-seccomp 36988 tap0
             └─37014 containerd

Apr 23 16:17:57 examplemachine containerd-rootless.sh[37014]: time="2021-04-23T16:17:57.196395748+09:00" level=info msg="loading plugin \"io.containerd.grpc.v1.introspection\"..." type=io.containerd.grpc.v1
Apr 23 16:17:57 examplemachine containerd-rootless.sh[37014]: time="2021-04-23T16:17:57.196448426+09:00" level=info msg="Start subscribing containerd event"
Apr 23 16:17:57 examplemachine containerd-rootless.sh[37014]: time="2021-04-23T16:17:57.196655545+09:00" level=info msg="Start recovering state"
Apr 23 16:17:57 examplemachine containerd-rootless.sh[37014]: time="2021-04-23T16:17:57.196784184+09:00" level=info msg="Start event monitor"
Apr 23 16:17:57 examplemachine containerd-rootless.sh[37014]: time="2021-04-23T16:17:57.196798860+09:00" level=info msg="Start snapshots syncer"
Apr 23 16:17:57 examplemachine containerd-rootless.sh[37014]: time="2021-04-23T16:17:57.196807353+09:00" level=info msg="Start cni network conf syncer"
Apr 23 16:17:57 examplemachine containerd-rootless.sh[37014]: time="2021-04-23T16:17:57.196811520+09:00" level=info msg="Start streaming server"
Apr 23 16:17:57 examplemachine containerd-rootless.sh[37014]: time="2021-04-23T16:17:57.196819091+09:00" level=info msg=serving... address=/run/containerd/containerd.sock.ttrpc
Apr 23 16:17:57 examplemachine containerd-rootless.sh[37014]: time="2021-04-23T16:17:57.196843099+09:00" level=info msg=serving... address=/run/containerd/containerd.sock
Apr 23 16:17:57 examplemachine containerd-rootless.sh[37014]: time="2021-04-23T16:17:57.196853937+09:00" level=info msg="containerd successfully booted in 0.037213s"
+ systemctl --user enable containerd.service
Created symlink /home/exampleuser/.config/systemd/user/default.target.wants/containerd.service → /home/exampleuser/.config/systemd/user/containerd.service.
[INFO] Installed "containerd.service" successfully.
[INFO] To control "containerd.service", run: `systemctl --user (start|stop|restart) containerd.service`
[INFO] To run "containerd.service" on system startup automatically, run: `sudo loginctl enable-linger exampleuser`
[INFO] ------------------------------------------------------------------------------------------
[INFO] Use `nerdctl` to connect to the rootless containerd.
[INFO] You do NOT need to specify $CONTAINERD_ADDRESS explicitly.

Usage

nerdctl run hello-world

Unlike rootless Docker, you do NOT need to specify $CONTAINERD_ADDRESS explicitly.

To start/stop the daemon, use systemctl --user <start|stop> containerd instead of systemctl <start|stop> containerd. The systemd unit file is located as ~/.config/systemd/user/containerd.service.

Tips

Enabling resource limitations (`nerdctl run --cpus`, `nerdctl run --memory`, …)

Resource-related flags of nerdctl run, such as --cpus, --memory, --blkio-weight, and --pids-limit can be used only when the following conditions are satisfied:

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

Changing the port forwarder

containerd 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/containerd.service.d/override.conf with the following content:

[Service]
Environment="CONTAINERD_ROOTLESS_ROOTLESSKIT_PORT_DRIVER=slirp4netns"

And then restart the daemon:

systemctl --user daemon-reload 
systemctl --user restart containerd

Starting containers on boot

You need to run sudo loginctl enable-linger .... See Getting Started/Login.

Resetting to factory settings

Run the following commands to remove all containers and configurations:

containerd-rootless-setuptool.sh uninstall
rootlesskit rm -rf ~/.local/share/containerd ~/.local/share/nerdctl ~/.config/containerd

Further information

See https://github.com/containerd/nerdctl/blob/master/docs/rootless.md