rootless.md

Rootless mode (Experimental)

Requirements:

• runc a00bf0190895aa465a5fbed0268888e2c8ddfe85 (Oct 15, 2018) or later
• Some distros such as Debian (excluding Ubuntu) and Arch Linux require sudo sh -c "echo 1 > /proc/sys/kernel/unprivileged_userns_clone".
• RHEL/CentOS 7 requires sudo sh -c "echo 28633 > /proc/sys/user/max_user_namespaces". You may also need sudo grubby --args="namespace.unpriv_enable=1 user_namespace.enable=1" --update-kernel="$(grubby --default-kernel)".
• newuidmap and newgidmap need to be installed on the host. These commands are provided by the uidmap package. For RHEL/CentOS 7, RPM is not officially provided but available at https://copr.fedorainfracloud.org/coprs/vbatts/shadow-utils-newxidmap/ .
• /etc/subuid and /etc/subgid should contain >= 65536 sub-IDs. e.g. penguin:231072:65536.
• To run in a Docker container with non-root USER, docker run --privileged is still required. See also Jessie's blog: https://blog.jessfraz.com/post/building-container-images-securely-on-kubernetes/

Set up

Setting up rootless mode also requires some bothersome steps as follows, but you can also use rootlesskit for automating these steps.

Terminal 1:

$ unshare -U -m
unshared$ echo $$ > /tmp/pid

Unsharing mountns (and userns) is required for mounting filesystems without real root privileges.

Terminal 2:

$ id -u
1001
$ grep $(whoami) /etc/subuid
penguin:231072:65536
$ grep $(whoami) /etc/subgid
penguin:231072:65536
$ newuidmap $(cat /tmp/pid) 0 1001 1 1 231072 65536
$ newgidmap $(cat /tmp/pid) 0 1001 1 1 231072 65536

Terminal 1:

unshared# buildkitd

• The data dir will be set to /home/penguin/.local/share/buildkit
• The address will be set to unix:///run/user/1001/buildkit/buildkitd.sock
• overlayfs snapshotter is not supported except Ubuntu-flavored kernel: http://kernel.ubuntu.com/git/ubuntu/ubuntu-artful.git/commit/fs/overlayfs?h=Ubuntu-4.13.0-25.29&id=0a414bdc3d01f3b61ed86cfe3ce8b63a9240eba7
• containerd worker is not supported ( pending PR: containerd/containerd#2006 )
• Network namespace is not used at the moment.
• Cgroups is disabled.

Terminal 2:

$ go get ./examples/build-using-dockerfile
$ build-using-dockerfile --buildkit-addr unix:///run/user/1001/buildkit/buildkitd.sock -t foo /path/to/somewhere

Set up (using a container)

Docker image is available as moby/buildkit:rootless.

$ docker run --name buildkitd -d --privileged -p 1234:1234  moby/buildkit:rootless --addr tcp://0.0.0.0:1234

docker run requires --privileged but the BuildKit daemon is executed as a normal user. See docker/cli#1347 for the ongoing work to remove this requirement

$ 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

$ go get ./examples/build-using-dockerfile
$ build-using-dockerfile --buildkit-addr tcp://127.0.0.1:1234 -t foo /path/to/somewhere