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rootless.md

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Rootless mode

Rootless mode allows running BuildKit daemon as a non-root user.

Distribution-specific hint

Using Ubuntu kernel is recommended.

Ubuntu

Debian GNU/Linux

  • Add kernel.unprivileged_userns_clone=1 to /etc/sysctl.conf (or /etc/sysctl.d) and run sudo sysctl -p
  • fuse-overlayfs snapshotter is used by default.
  • To use overlayfs snapshotter (recommended), run sudo modprobe overlay permit_mounts_in_userns=1 (Debian-specific kernel patch, introduced in Debian 10). Put the configuration to /etc/modprobe.d for persistence.

Arch Linux

  • Add kernel.unprivileged_userns_clone=1 to /etc/sysctl.conf (or /etc/sysctl.d) and run sudo sysctl -p
  • fuse-overlayfs snapshotter is used by default if running kernel >= 4.18. Otherwise only native snapshotter can be used.

Fedora

  • If you don't have the latest runc (>= v1.0.0-rc91) installed and you have crun instead, you need to run buildkitd with --oci-worker-binary=crun.
  • fuse-overlayfs snapshotter is used by default.

RHEL/CentOS 8

  • No preparation is needed.
  • fuse-overlayfs snapshotter is used by default.

RHEL/CentOS 7

  • Add user.max_user_namespaces=28633 to /etc/sysctl.conf (or /etc/sysctl.d) and run sudo sysctl -p
  • Old releases (<= 7.6) require extra configuration steps.
  • Only native snapshotter can be used.

Container-Optimized OS from Google

  • ⚠️ Currently unsupported. See #879.

Known limitations

  • fuse-overlayfs is used instead of overlayfs on most distros.
  • Network mode is always set to network.host.
  • No support for containerd worker

Running BuildKit in Rootless mode

RootlessKit needs to be installed.

$ rootlesskit buildkitd
$ buildctl --addr unix:///run/user/$UID/buildkit/buildkitd.sock build ...

To isolate BuildKit daemon's network namespace from the host (recommended):

$ rootlesskit --net=slirp4netns --copy-up=/etc --disable-host-loopback buildkitd

Troubleshooting

If facing an error related to fuse-overlayfs, try running buildkitd with --oci-worker-snapshotter=native:

$ rootlesskit buildkitd --oci-worker-snapshotter=native

Containerized deployment

Kubernetes

See ../examples/kubernetes.

Docker

$ docker run \
  --name buildkitd \
  -d \
  --security-opt seccomp=unconfined \
  --security-opt apparmor=unconfined \
  --device /dev/fuse \
  moby/buildkit:rootless --oci-worker-no-process-sandbox
$ buildctl --addr docker-container://buildkitd build ...

If you don't mind using --privileged (almost safe for rootless), the docker run flags can be shorten as follows:

$ docker run --name buildkitd -d --privileged moby/buildkit:rootless

About --device /dev/fuse

Adding --device /dev/fuse to the docker run arguments is required only if you want to use fuse-overlayfs snapshotter.

About --oci-worker-no-process-sandbox

By adding --oci-worker-no-process-sandbox to the buildkitd arguments, BuildKit can be executed in a container without adding --privileged to docker run arguments. However, you still need to pass --security-opt seccomp=unconfined --security-opt apparmor=unconfined to docker run.

Note that --oci-worker-no-process-sandbox allows build executor containers to kill (and potentially ptrace depending on the seccomp configuration) an arbitrary process in the BuildKit daemon container.

To allow running rootless buildkitd without --oci-worker-no-process-sandbox, run docker run with --security-opt systempaths=unconfined. (For Kubernetes, set securityContext.procMount to Unmasked.)

The --security-opt systempaths=unconfined flag disables the masks for the /proc mount in the container and potentially allows reading and writing dangerous kernel files, but it is safe when you are running buildkitd as non-root.

Change UID/GID

The moby/buildkit:rootless image has the following UID/GID configuration:

Actual ID (shown in the host and the BuildKit daemon container) Mapped ID (shown in build executor containers)
1000 0
100000 1
... ...
165535 65536 
$ docker exec buildkitd id
uid=1000(user) gid=1000(user)
$ docker exec buildkitd ps aux
PID   USER     TIME   COMMAND
    1 user       0:00 rootlesskit buildkitd --addr tcp://0.0.0.0:1234
   13 user       0:00 /proc/self/exe buildkitd --addr tcp://0.0.0.0:1234
   21 user       0:00 buildkitd --addr tcp://0.0.0.0:1234
   29 user       0:00 ps aux
$ docker exec cat /etc/subuid
user:100000:65536

To change the UID/GID configuration, you need to modify and build the BuildKit image manually.

$ vi Dockerfile
$ make images
$ docker run ... moby/buildkit:local-rootless ...