Defaults

Compile-time defaults live in the defaults/ package. They're per-OS so the daemon picks platform-appropriate values when no config is supplied.

Default paths and addresses

The values used at the time of this wiki (subject to platform):

Constant	Linux	Windows	Source
DefaultRootDir	/var/lib/containerd	C:\ProgramData\containerd\root	defaults/defaults.go
DefaultStateDir	/run/containerd	C:\ProgramData\containerd\state	defaults/defaults.go
DefaultAddress	/run/containerd/containerd.sock	\\\\.\\pipe\\containerd-containerd	defaults/defaults.go
DefaultDebugAddress	/run/containerd/debug.sock	\\\\.\\pipe\\containerd-debug	defaults/defaults.go
DefaultFIFODir	/run/containerd/fifo	n/a	defaults/defaults.go
DefaultRuntime	io.containerd.runc.v2	io.containerd.runhcs.v1	defaults/defaults.go
DefaultConfigDir	/etc/containerd	C:\ProgramData\containerd	defaults/defaults.go
DefaultConfigFile	/etc/containerd/config.toml	C:\ProgramData\containerd\config.toml	defaults/defaults.go

gRPC message size limits

const (
    DefaultMaxRecvMsgSize = 16 << 20 // 16 MiB
    DefaultMaxSendMsgSize = 16 << 20
)

These match Docker's defaults and are large enough for OCI manifests but small enough to bound resource usage. Configurable via [grpc] max_recv_message_size = ....

Default runtimes

Each platform's CRI default runtime:

• Linux: io.containerd.runc.v2
• Windows: io.containerd.runhcs.v1

The CRI plugin uses defaults.DefaultRuntime if the operator didn't specify a default_runtime_name.

Default snapshotter

• Linux: overlayfs
• Windows: windows

Set in CRI config via snapshotter. The Go client falls back to the daemon's containerd.WithImageHandler defaults — see client/client.go.

Default GC scheduler thresholds

From plugins/gc/scheduler.go:

Field	Default	Effect
pause_threshold	0.02	GC won't run if it would consume more than 2% of CPU
deletion_threshold	0	Trigger GC after this many deletes (0 = no auto-trigger)
mutation_threshold	100	Trigger GC after this many mutations
schedule_delay	0s	Delay between scheduled GC runs
start_delay	100ms	Delay before first GC after daemon start

Where to override

Most defaults can be set via config.toml. Values that aren't surfaced in config are compile-time only — change defaults/ and rebuild.