ipfs/kubo · error

unknowm mhType %d

Error message

unknowm mhType %d

What it means

BlockAPI.Put validates the requested multihash type by looking up px.MhType in the mh.Codes table; if the code is not a registered multihash function it returns this error (note the 'unknowm' typo in the message). The client refuses to ask the daemon to build a block with a hash function it cannot name.

Source

Thrown at client/rpc/block.go:43

func (s *blockStat) Size() int {
	return s.BSize
}

func (s *blockStat) Path() path.ImmutablePath {
	return path.FromCid(s.cid)
}

func (api *BlockAPI) Put(ctx context.Context, r io.Reader, opts ...caopts.BlockPutOption) (iface.BlockStat, error) {
	options, err := caopts.BlockPutOptions(opts...)
	px := options.CidPrefix
	if err != nil {
		return nil, err
	}

	mht, ok := mh.Codes[px.MhType]
	if !ok {
		return nil, fmt.Errorf("unknowm mhType %d", px.MhType)
	}

	var cidOptKey, cidOptVal string
	switch {
	case px.Version == 0 && px.Codec == cid.DagProtobuf:
		// ensure legacy --format=v0 passes as BlockPutOption still works
		cidOptKey = "format"
		cidOptVal = "v0"
	default:
		// pass codec as string
		cidOptKey = "cid-codec"
		cidOptVal = mc.Code(px.Codec).String()
	}

	req := api.core().Request("block/put").
		Option("mhtype", mht).
		Option("mhlen", px.MhLength).
		Option(cidOptKey, cidOptVal).

View on GitHub (pinned to 329838acdf)

Solutions

1. Use a registered multihash constant, e.g. mh.SHA2_256 (0x12), mh.SHA2_512 (0x40), mh.SHA3_256 (0x16), mh.BLAKE2B_MIN+31, or mh.IDENTITY (0x00 is NOT identity; use mh.IDENTITY for raw identity hashes).
2. If you need a custom multihash code, register it with mh.Codes before calling Put so the lookup succeeds.
3. Check the value you pass to opts.Block.MhType against the table in github.com/multiformats/go-multihash (mh.Codes) to confirm it is registered.

Example fix

// before
blk, err := api.Block().Put(ctx, r, opts.Block.MhType(0x00).Codec(cid.DagProtobuf).Format("cbor"))
// after
blk, err := api.Block().Put(ctx, r, opts.Block.MhType(mh.SHA2_256).Codec(cid.DagProtobuf).Format("cbor"))

if _, ok := mh.Codes[mhType]; !ok {
    return fmt.Errorf("mhType %d is not a registered multihash code", mhType)
}
// proceed to api.Block().Put with opts.Block.MhType(mhType)

When it happens

Trigger: Calling api.Block().Put(ctx, reader, opts.Block.MhType(x).Codec(cidCode).Format(format)) where x is 0, a negative value, or an unregistered/proprietary multihash code not present in mh.Codes.

Common situations: Hand-written constants for MhType (e.g. 0x00 or a typo'd hex value), custom hash functions registered only on the daemon but not in the client's multihash table, or copying option values from an old example that predates the multihash registry.

Related errors

• only sha2-255-32 is allowed with CIDv0
• unknowm mhType %d
• Import.HashFunction unrecognized: %q
• unrecognized hash function: %q
• only dag-pb is allowed with CIDv0

AI-assisted analysis of ipfs/kubo@329838acdf (2026-09-03). Data as JSON: /api/errors/77c22bdd7034eb6e. Report an issue: GitHub.