Proof-of-work mining with Ethash

Blockchains grow when individual nodes create valid blocks and distribute them to their peers who check the blocks and add them to their own local databases.

Nodes that add blocks are rewarded with ether payouts. On Ethereum Mainnet, the proof-of-stake consensus engine randomly selects a node to produce each block.

Ethereum wasn't always secured this way. Originally, a proof-of-work based consensus mechanism was used instead. Under proof-of-work, block producers are not selected randomly in each slot. Instead they compete for the right to add a block. The node that is fastest to compute a certain value that can only be found using brute force calculations is the one that gets to add a block. Only if a node can demonstrate that they have calculated this value, and therefore expended energy, will their block be accepted by other nodes. This process of creating blocks and securing them using proof-of-work is known as "mining".

Much more information about mining, including details about the specific algorithm ("Ethash") used by Ethereum nodes is available on ethereum.org.

CPU vs GPU

Everything required to mine on a CPU used to come bundled with Geth. However, to mine using GPUs an additional piece of third-party software was required. The most commonly used GPU mining software is Ethminer.

Regardless of the mining method, the blockchain must be fully synced before mining is started, otherwise the miner will build on an outdated side chain, meaning block rewards will not be recognized by the main network.

GPU Mining

Installing Ethminer

The Ethminer software can be installed from a downloaded binary or built from source. The relevant downloads and installation instructions are available from the Ethminer GitHub. Standalone executables are available for Linux, macOS and Windows.

Using Ethminer with Geth

An account to receive block rewards must first be defined. The address of the account is all that is required to start mining - the mining rewards will be credited to that address. This can be an existing address or one that is newly created by Geth. More detailed instructions on creating and importing accounts are available on the Account Management page.

The account address can be provided to --mining.etherbase when Geth is started. This instructs Geth to direct any block rewards to this address. Once started, Geth will sync the blockchain. If Geth has not connected to this network before, or if the data directory has been deleted, this can take several days. Also, enable HTTP traffic with the --http command.

geth --http --miner.etherbase 0xC95767AC46EA2A9162F0734651d6cF17e5BfcF10

The progress of the blockchain syncing can be monitored by attaching a JavaScript console in another terminal. More detailed information about the console can be found on the Javascript Console page. To attach and open a console:

geth attach http://127.0.0.1:8545

Then in the console, to check the sync progress:

eth.syncing

If the sync is progressing correctly the output will look similar to the following:

Once the blockchain is synced, mining can begin. In order to begin mining, Ethminer must be run and connected to Geth in a new terminal. OpenCL can be used for a wide range of GPUs, CUDA can be used specifically for Nvidia GPUs:

#OpenCL
ethminer -v 9 -G -P http://127.0.0.1:8545

#CUDA
ethminer -v -U -P http://127.0.0.1:8545

Ethminer communicates with Geth on port 8545 (Geth's default RPC port) but this can be changed by providing a custom port to the http.port command. The corresponding port must also be configured in Ethminer by providing -P http://127.0.0.1:<port-number>. This is necessary when multiple instances of Geth/Ethminer will coexist on the same machine.

If using OpenCL and the default for ethminer does not work, specifying the device using the --opencl--device X command is a common fix. X is an integer 1, 2, 3 etc. The Ethminer -M (benchmark) command should display something that looks like:

Note that the Geth command miner.hashrate only works for CPU mining - it always reports zero for GPU mining. To check the GPU mining hashrate, check the logs ethminer displays to its terminal.

More verbose logs can be configured using -v and a value between 0-9. The Ethash algorithm is memory-hard and requires a large dataset to be loaded into memory. Each GPU requires 4-5 GB of RAM. The error message Error GPU mining. GPU memory fragmentation? indicates that there is insufficient memory available.

CPU Mining with Geth

When Geth is started it is not mining by default. Unless it is specifically instructed to mine, it acts only as a node, not a miner. Geth starts as a (CPU) miner if the --mine flag is provided.

geth --mine

CPU mining can also be started and stopped at runtime using the console.

miner.start();
true;
miner.stop();
true;

Note that mining only makes sense if you are in sync with the network (since you mine on top of the consensus block). Therefore the blockchain downloader/synchroniser will delay mining until syncing is complete, and after that mining automatically starts unless you cancel with miner.stop().

Like with GPU mining, an etherbase account must be set. This defaults to the primary account in the keystore but can be set to an alternative address using the --miner.etherbase command:

geth --miner.etherbase '0xC95767AC46EA2A9162F0734651d6cF17e5BfcF10' --mine

If there is no account available an account will be created and automatically configured to be the coinbase. The Javascript console can be used to reset the etherbase account at runtime:

miner.setEtherbase(eth.accounts[2])

Note that your etherbase does not need to be an address of a local account, it just has to be set to an existing one.

There is an option to add extra data (32 bytes only) to the mined blocks. By convention this is interpreted as a unicode string, so it can be used to add a short vanity tag using miner.setExtra in the Javascript console.

miner.setExtra("ΞTHΞЯSPHΞЯΞ")

The console can also be used to check the current hashrate in units H/s (Hash operations per second):

eth.hashrate
 712000

After some blocks have been mined, the etherbase account balance with be >0. Assuming the etherbase is a local account:

eth.getBalance(eth.coinbase).toNumber();
 '34698870000000'

It is also possible to check which blocks were mined by a particular miner (address) using the following code snippet in the Javascript console:

function minedBlocks(lastn, addr) {
  addrs = [];
  if (!addr) {
    addr = eth.coinbase;
  }
  limit = eth.blockNumber - lastn;
  for (i = eth.blockNumber; i >= limit; i--) {
    if (eth.getBlock(i).miner == addr) {
      addrs.push(i);
    }
  }
  return addrs;
}

// scans the last 1000 blocks and returns the blocknumbers of blocks mined by your coinbase
// (more precisely blocks the mining reward for which is sent to your coinbase).
minedBlocks(1000, eth.coinbase)[(352708, 352655, 352559)];

The etherbase balance will fluctuate if a mined block is re-org'd out of the canonical chain. This means that when the local Geth node includes the mined block in its own local blockchain the account balance appears higher because the block rewards are applied. When the node switches to another version of the chain due to information received from peers, that block may not be included and the block rewards are not applied.

The logs show locally mined blocks confirmed after 5 blocks.

Summary

The page describes how to start Geth as a mining node. Mining can be done on CPUs - in which case Geth's built-in miner can be used - or on GPUs which requires third party software. Mining is no longer used to secure Ethereum Mainnet.