Bitcoin BLAKE2b + DATUM on Umbrel
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Umbrel · Bitcoin Knots · DATUM · BLAKE2b

Set up BLAKE2b mining on Umbrel.

Follow this page from top to bottom. It covers Bitcoin Knots, DATUM, and connecting a BLAKE2b miner. Solo mining is the default; pool mining and Tor-only peers are optional.

If you get stuck: there is a troubleshooting section at the bottom. If something is wrong or a step is still unclear, open an issue on GitHub so I can fix the guide and make that step clearer.
00

Before you start

You need an Umbrel, a BLAKE2b miner that accepts a custom Stratum server, and a Bitcoin address you control.

Only use a public Bitcoin address. Never put a seed phrase or private key into DATUM.
If your miner does not accept a custom pool

You need firmware that lets you enter your own Stratum host. A miner locked to a vendor pool cannot connect to your DATUM gateway.

01

What are you starting with?

Pick your situation. The instructions stay on this page.

02

Get a payout address

The move to BLAKE2b did not change Bitcoin addresses. Any address you controlled on the pre-BLAKE2b chain is still a valid address on the BLAKE2b chain, so you can reuse one you already had.

Or open a wallet you control, choose Receive, and copy a new address. If it is a hardware wallet, verify it on the device. Keep the address handy; you will use it in DATUM and as your miner username.

Not sure you control the address?

Stop and check. Mining rewards sent to the wrong address cannot be recovered.

03

Add the Retropex app store

  1. From the Umbrel home screen, open App Store.
  2. Open the ⋯ menu in the App Store and choose Community App Stores.
  3. Choose Add or Add Community App Store.
  4. Paste this repository URL and confirm:
https://github.com/Retropex/Bitcoin-store

When it finishes loading, Retropex will appear as another store you can open from the App Store.

Retropex does not show up

Reload the App Store and make sure the URL is exactly https://github.com/Retropex/Bitcoin-store.

04

Install or update Bitcoin Knots

You need a Knots build with BLAKE2b support. If you already have Knots, update it in place so you keep the blockchain you already downloaded.

Using the August 2026 RC4 / rehearsal build?
These steps are dated. Use them only for the August 2026 RC4/rehearsal path. Skip this dropdown once the BLAKE2b release is available normally.

Expose the RC4 update

In Umbrel open Settings → Advanced settings → Terminal → umbrelOS. Keep the Umbrel updates page open in another tab.

cd umbrel/app-stores/getumbrel-umbrel-apps-github-* && git remote add leo https://github.com/Retropex/umbrel-apps.git && git fetch --all && git switch rc4

Reload the updates page and install Bitcoin Knots 1.2.14, which contains 29.4.1.knots20260508rc4. If Umbrel later offers 1.2.13 during this RC procedure, do not take that downgrade.

Add the RC4 headline

Open Bitcoin Knots → Settings → Advanced → Custom bitcoin.conf overrides and add:

blake2b_headline=8-30 NYPost Deride And Conquer

Click Save overrides after making the change.

Add BLAKE2b peers

Give Knots some known BLAKE2b peers before you wait for it to catch up. Otherwise it can spend time connecting to ordinary SHA256 peers that cannot advance the BLAKE2b branch.

For current RC4 clearnet IPs, use the RC4 peer thread on Discord. Add the current addresses there as addnode=IP:PORT lines in Custom bitcoin.conf overrides.

You can also add these known onion peers. They work as BLAKE2b peer examples and are useful if you prefer Tor:

addnode=4zbweaaovjnwnybsewebrmixxqgvvyrjswpytehpjdzzilavxgwaqpad.onion:8333
addnode=ydmycqwbway27bwtbiutcfu2axwf3wwuo42fs7jmvbq4xky3m3hycbad.onion:9333
addnode=adq3l7pjwpowiq2see3zafmsgkfqrus375meczhz5be47xciq5rpzcqd.onion:8333
addnode=qdvgur56ajkbeo4u7lxmwguxqqeqi3chtml7z3taw2gn4qvlhvl4wzqd.onion:8333
addnode=hpwjpbtcuiedebbrkbfmdaa7tubndjlidkmigedelhbhbaboypabnyad.onion:8333

Click Save overrides after adding peers. These community peers can change or go offline, so check Discord if none connect.

Let Knots catch up

During the rehearsal, the BLAKE2b branch started at block 961,640. Knots may roll back to the last shared block, then sync forward on the BLAKE2b branch using the peers you added above.

Clearnet enabled or Tor-only?

Clearnet enabled: this is the simplest setup. Leave normal networking enabled and add known BLAKE2b clearnet peers from the Discord thread. You can keep the onion addnode lines too.

Clearnet disabled / Tor-only: do not add clearnet IPs. Use the onion peers above and add this line to the same bitcoin.conf overrides:

onlynet=onion

Click Save overrides. Knots will then make Bitcoin peer connections over Tor only. If you end up with zero peers, remove onlynet=onion temporarily and test with default networking.

Knots will not start or sync after the RC update

Check the version, headline, and peer entries. If the RC update disappears from Umbrel, run the RC4 store-switch command again and immediately reload the updates page.

05

Let the BLAKE2b chain sync

Open Bitcoin Knots and watch the block height. You want peers connected and the height moving upward.

Open mempool.guide to see the latest BLAKE2b block. Compare that height with the height shown by your Knots node so you know how far behind you are.

Wait until Knots reaches the current tip before you start mining. A rollback during the transition does not mean the whole blockchain was deleted; Knots can reuse your existing data and follow the new branch from the fork point.

The block height is not moving

Check that you are on a BLAKE2b-capable Knots build and that your connected peers are BLAKE2b peers. Go back to section 4 and add current peers from Discord or the onion peers listed there.

06

Install DATUM (blake2b)

  1. Open App Store on Umbrel.
  2. Open the Retropex community store you added earlier.
  3. Install DATUM (blake2b).
  4. Open it when installation finishes.
  5. If you need the login, right-click the DATUM icon on the Umbrel home screen and choose Show default credentials.
Using the August 2026 RC4 / rehearsal build?

Update DATUM after Knots

Finish the Knots RC4 update first, then update or install DATUM (blake2b). After it starts, check the payout address and solo/pool setting again.

Check the primary coinbase tag

Open Settings → Advanced settings → Terminal → DATUM (blake2b) and run:

grep -n "coinbase_tag" /app/conf/datum_gateway_config.json

If the primary tag specifically shows Catbus, replace it:

sed -i 's/"coinbase_tag_primary": "Catbus"/"coinbase_tag_primary": "8-30 NYPost Deride And Conquer"/' /app/conf/datum_gateway_config.json

Restart DATUM afterward. Do not run the replacement command if Catbus is not in the file.

DATUM stays on Initialising

Make sure Bitcoin Knots is running, on the BLAKE2b chain, and fully caught up.

07

Configure DATUM

Start with solo mining. Your own Knots node builds the block template and your local DATUM gateway sends that work to your miner.

  1. Open DATUM → Config.
  2. Put your payout address in Bitcoin Address.
  3. Add a short Coinbase Tag if you want one.
  4. Set Collaborative reward sharing to never (non-pooled only).
  5. Save.
08

Point your miner at DATUM

  1. Find your Umbrel's local IP address in Umbrel settings.
  2. Open your miner's pool or Stratum settings.
  3. Use your Umbrel IP with port 23339.
  4. Use your payout address as the username. You can add .workername to the end.
  5. Leave the password blank, or use any value if the miner requires one.
  6. If it asks for an algorithm, choose its BLAKE2b/Sia-compatible mode.
  7. Save and restart the miner if needed.
stratum+tcp://YOUR_UMBREL_IP:23339

Example: if your Umbrel is 192.168.1.50, the pool/Stratum address is stratum+tcp://192.168.1.50:23339.

The miner cannot connect

Check the Umbrel IP, make sure both devices are on the same LAN, and use port 23339.

09

Check that it is working

Open DATUM → Clients. Your miner should show up as a connected Stratum client.

FieldWhat you should see
Auth UsernameYour payout address / worker
SubbedAn active job/subscription
UserAgentYour miner or firmware name
Last AcceptedMay stay N/A until the first valid share
HashrateMay take an accepted share before it appears
N/A does not automatically mean something is wrong. Finding a share is random. A miner can be connected and hashing before DATUM has enough accepted work to show a hashrate.
The miner appears, but shares are rejected

Open the DATUM logs and look for the exact reject reason. If the miner never appears in Clients at all, fix the miner-to-Umbrel connection first.

10

Troubleshooting

How do I check my Bitcoin Knots version?

Open Settings → Advanced settings → Terminal → Bitcoin Knots and run bitcoind --version. If you were running Knots before the BLAKE2b/RDTS work, make sure you did not stay on an older pre-RDTS build.

Knots has peers but the height is not moving

Make sure you added known BLAKE2b peers in section 4. Ordinary SHA256 peers will not move you forward on the BLAKE2b branch. Compare your height to mempool.guide.

I use Tor-only and have zero peers

Check the onion addnode entries in section 4. Community peers can go offline. Check the Discord peer thread for replacements. If needed, temporarily remove onlynet=onion and test default networking.

DATUM says Initialising

Make sure Knots is running, caught up to the BLAKE2b tip, and on a BLAKE2b-capable build.

The miner cannot connect to DATUM

Use your Umbrel's LAN IP and port 23339. Make sure the miner and Umbrel can reach each other on the local network.

Last Accepted is N/A

If the miner is connected and subscribed, give it time. The first valid share can take a while.

VDiff is much higher than I set

When pooled, the upstream DATUM pool can impose its own minimum difficulty. That value can override your lower local setting.

DATUM still has the old Catbus coinbase tag

Open the RC4 dropdown in the DATUM section and run the coinbase-tag check there.

Still stuck, found an error, or think a step could be clearer? Open an issue on GitHub so I can update the site. Include your Knots version, DATUM version, miner model, and the exact error. Never post a seed phrase or private key.

11

References