Solo mining on testnet4

These RC3 binaries are not the published files on bitcoinknots.org. Download v29.4.1.knots20260508rc3 for your architecture (for example x86_64-linux-gnu or aarch64-linux-gnu) from:

test.bitcoinknots.org RC3 directory

Check the build against SHA256SUMS and SHA256SUMS.asc in that directory. Sync with chain=testnet4.

1. Knots on testnet4

Minimal bitcoin.conf:

chain=testnet4
server=1
txindex=1
blake2b_headline=Catbus

[testnet4]
rpcport=8332
rpcbind=127.0.0.1
rpcallowip=127.0.0.1
rpcuser=USER
rpcpassword=PASS
# optional: notify DATUM on new blocks
blocknotify=curl -fsS -o /dev/null http://127.0.0.1:7152/NOTIFY

Default P2P port is 48333, not 8333.

bitcoin-cli -rpcport=8332 getblockchaininfo
bitcoin-cli -rpcport=8332 getdeploymentinfo   # hardfork.height == 150027

2. DATUM Gateway fork

git clone https://github.com/justinfilip/datum_gateway.git
cd datum_gateway
# build per README (cmake + libmicrohttpd, jansson, curl, libsodium, …)

Use a build that includes commit 56c31f4 (pow: Include header-v2 bit in BLAKE2b H1 commitment version) or later. Without that change, share proof of work will not match Knots RC3 GetHash.

Example datum_gateway_config.json:

{
  "bitcoind": {
    "rpcuser": "USER",
    "rpcpassword": "PASS",
    "rpcurl": "http://127.0.0.1:8332"
  },
  "stratum": { "listen_addr": "0.0.0.0", "listen_port": 23334 },
  "api": {
    "listen_addr": "0.0.0.0",
    "listen_port": 7152,
    "admin_password": "CHANGE_ME",
    "modify_conf": true
  },
  "mining": {
    "pool_address": "tb1q…your_testnet4_address…",
    "coinbase_tag_primary": "MyTag",
    "coinbase_tag_secondary": "Catbus",
    "pow_algorithm": "auto"
  },
  "datum": { "pool_host": "", "pooled_mining_only": false }
}

datum_gateway -c /path/to/datum_gateway_config.json

• UI: http://HOST:7152 (digest auth uses admin_password)
• Stratum: stratum+tcp://HOST:23334

Keep "pow_algorithm": "auto". Do not force "blake2b" before height 150027. Set coinbase_tag_secondary to exactly Catbus. Knots requires the headline bytes in the coinbase. This DATUM build does not copy coinbaseaux.blake2b_headline into the coinbase for you, so the secondary tag is how those bytes get into scriptSig.

3. Miners

Point the miner at your stratum URL. The username can be any worker name DATUM accepts. A payout address is a common choice.

After activation, confirm GBT advertises blake2b:

bitcoin-cli -rpcport=8332 getblocktemplate '{"rules":["segwit","blake2b"]}'
# expect "!blake2b" in rules; coinbaseaux.blake2b_headline should be hex for "Catbus"

4. Optional peer

addnode=OTHER_HOST:48333

What working looks like

Before activation (tip below 150027)

• Knots syncs testnet4. getdeploymentinfo shows hardfork height 150027 and active: false.
• GBT does not yet require blake2b: no !blake2b in rules. coinbaseaux is typically empty even if the client advertises blake2b support.
• DATUM with auto serves SHA256d stratum jobs. SHA256d miners connect, get work, and submit shares.
• BLAKE2b and BLAKE2b-sia miners are not useful yet. They need BLAKE2b jobs after the hardfork.
• Quiet testnet4 often sits at minimum difficulty and moves about every 20 minutes unless someone is mining.

At and after activation (tip 150027 or higher)

• getdeploymentinfo reports hardfork active: true.
• GBT from a client that supports blake2b shows !blake2b and coinbaseaux.blake2b_headline (hex for Catbus).
• DATUM auto switches to BLAKE2b / header v2 jobs (Sia-style notify: commitment coinb1, JSON merkle [], longer ntime and nonce fields, and related fields).
• A BLAKE2b or BLAKE2b-sia miner connects, hashes, and submits shares. Hashrate shows up in DATUM stats and the UI.
• On a real block you should see BLOCK FOUND - <hash>, and the new tip hash should be that same hash.
• Knots accepts the block via submitblock. A second log line saying duplicate is normal. DATUM submits twice; one path wins.
• You should not see intermittent high-hash on valid BLAKE2b or BLAKE2b-sia blocks if DATUM is at 56c31f4 or later. Older builds hashed H1 without wire bit 0x80000000, so DATUM's block hash often disagreed with Knots: about a coin-flip on easy regtest, and almost all rejects at real difficulty.

Quick health checks

1. Miners stay connected and jobs refresh on new tips.
2. Shares are accepted. You are not flooded with unknown-work or high-hash rejects.
3. After the hardfork, the BLOCK FOUND hash equals the new chain tip.
4. The node has blake2b_headline=Catbus, DATUM's secondary tag is Catbus, and those headline bytes are present in the coinbase.

Common mistakes

• Forcing "pow_algorithm": "blake2b" before 150027 produces bad templates and rejects.
• If the node is set to Catbus but the coinbase never contains Catbus, Knots rejects the block with Headline is wrong.
• DATUM older than 56c31f4 can print BLOCK FOUND and then intermittent or frequent high-hash.
• Peering on 8333 by mistake. testnet4 P2P is 48333.

Checklist

1. Knots RC3 from the URL above, blake2b_headline=Catbus, and a synced testnet4 chain.
2. DATUM fork at 56c31f4 or later, auto, and secondary tag Catbus.
3. Before the hardfork: SHA256d miners. After it: BLAKE2b and BLAKE2b-sia miners on stratum port 23334.
4. Watch the tip reach 150027, then start BLAKE2b miners.
5. Confirm the BLOCK FOUND hash matches the tip. Ignore a benign dual-submit duplicate.