The Sysbox Manager (aka sysbox-mgr) is a daemon that provides miscellaneous services to other sysbox components.

Currently it provides these services:

• Subid allocation: allocates a common range of subuid and subgids for all system containers; service is invoked by sysbox-runc.

• Shiftfs marking: creates shiftfs marks on host directories on which shiftfs will be mounted. Handles redundant mounts/unmounts of shiftfs on the same directory.

• Mount ownership changes: changes ownership on host directories that are bind-mounted into the sys container and on top of which shiftfs mounting is not possible.

• Docker-store Volume Management: creates a directory on the host that is mounted into the system container's /var/lib/docker. This way, the overlayfs over overlayfs scenario created by running docker-in-docker is avoided.

• Kubelet-store Volume Management: creates a directory on the host that is mounted into the system container's /var/lib/kubelet. This is needed to avoid shiftfs mounts over this directory in the sys container, as kubelet does not support it.

• Docker-store Volume Management: creates a directory on the host that is mounted into the system container's /var/lib/containerd/io.containerd.snapshotter.v1.overlayfs. This way, the overlayfs over overlayfs scenario created by running containerd-in-docker is avoided.

In the future it's expected to provide further services to sysbox-runc as well as sysbox-fs.

sysbox-mgr is built with the sysbox Makefile. Refer to that sysbox README file for details.

sysbox-mgr listens on a unix-domain socket for gRPC from other sysbox components.

Currently a single gRPC is used (between sysbox-runc and sysbox-mgr).

In the future other gRPCs may be created (e.g,. for communication between sysbox-fs and sysbox-mgr).