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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

No preparation is needed.
overlayfs snapshotter is used by default (Ubuntu-specific kernel patch).

Debian GNU/Linux 10

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.

Debian GNU/Linux 9

Add kernel.unprivileged_userns_clone=1 to /etc/sysctl.conf (or /etc/sysctl.d) and run sudo sysctl -p
Only native snapshotter can be used.

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 31

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

Fedora 30

No preparation is needed.
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 ...

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 ...

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