Systems

The "systems" lens covers the major in-process subsystems of the containerd daemon — components that aren't a single binary or a single plugin, but that span multiple files and tie a feature area together.

System	Code under	Responsibility
Plugin runtime	cmd/containerd/builtins/, cmd/containerd/server/, plugins/types.go	Plugin registration, dependency-ordered initialization, proxy plugin wiring
Runtime v2	core/runtime/v2/, cmd/containerd-shim-runc-v2/	Daemon-side shim manager: spawn shims, dispatch tasks, reap exits
Content store	core/content/, plugins/content/local/	Content-addressable blob storage
Metadata store	core/metadata/, plugins/metadata/	Bbolt-backed unified store for images, containers, leases, sandboxes, snapshots metadata
Snapshotters	core/snapshots/, plugins/snapshots/*	Layered rootfs implementations: overlay, btrfs, devmapper, native, blockfile, erofs, windows, lcow
Image distribution	core/remotes/, core/images/, core/transfer/, plugins/transfer/, core/unpack/	Pull, push, import, export, unpack
Sandbox controller	core/sandbox/, plugins/sandbox/, internal/cri/server/podsandbox/	Pod-sandbox abstraction (shared netns/IPC for a group of containers)
CRI plugin	internal/cri/, plugins/cri/	Kubernetes Container Runtime Interface implementation
Garbage collection	core/metadata/gc.go, plugins/gc/, core/gc/	Reference-graph + lease-driven GC scheduler
Events	core/events/, plugins/events/, plugins/services/events/	In-process event exchange and gRPC fan-out
Streaming	core/streaming/, plugins/streaming/	Bidirectional stream broker used by transfer and CRI exec/attach
Mount manager	core/mount/, plugins/mount/, plugins/mount/erofs, plugins/mount/fsview	Pluggable mount handler abstraction
NRI	internal/nri/, plugins/nri/, core/nri/	Node Resource Interface adapter for third-party runtime hooks
Tracing & metrics	pkg/tracing/, plugins/server/metrics/, plugins/server/internal/, cmd/containerd/builtins/tracing.go	OpenTelemetry tracing and Prometheus metrics

Many of these systems are themselves implemented as one or more plugins; see Plugins for the registration-level view.