Full node

A subset of full nodes also accept incoming connections and upload old blocks to other peers on the network. This happens if the software is run with -listen=1 as is default. Contrary to some popular misconceptions, being an archival node is not necessary to being a full node. If a user's bandwidth is constrained then they can use -listen=0, if their disk space is constrained they can use pruning, all the while still being a fully-validating node that enforces bitcoin's consensus rules and contributing to bitcoin's overall security.

Running a full node is the only way you can use Bitcoin in a trustless way. You will know for sure that all the rules of Bitcoin are being followed, for example that no bitcoins are spent not belonging to the owner, that no coins were spent twice, that no inflation happens outside of the schedule and that all the rules needed to make the system work (e.g. difficulty) are followed. Full nodes are currently the most private way to use Bitcoin, with nobody else learning which bitcoin addresses belong to you. Full nodes are the most secure way to use Bitcoin, they do not suffer from many attacks that affect lightweight wallets.

This is by far the most important reason for running a full node, though it is a little difficult to understand.

As explained previously, full nodes enforce the consensus rules no matter what. However, lightweight nodes do not do this. Lightweight nodes do whatever the majority of mining power says. Therefore, if most of the miners got together to increase their block reward, for example, lightweight nodes would blindly go along with it. If this ever happened, the network would split such that lightweight nodes and full nodes would end up on separate networks, using separate currencies. People using lightweight nodes would be unable to transact with people using full nodes. If all businesses and many users are using full nodes, then this network split is not a critical problem because users of lightweight clients will quickly notice that they can't send or receive bitcoins to/from most of the people who they usually do business with, and so they'll stop using Bitcoin until the evil miners are overcome, which is the appropriate response. However, if almost everyone on the network is using lightweight nodes in this situation, then everyone would continue being able to transact with each other, and so Bitcoin could very well end up "hijacked" by evil miners.

In practice, miners are unlikely to attempt anything like the above scenario as long as full nodes are prevalent because the miners would lose a lot of money. But the incentives completely change if everyone uses lightweight nodes. In that case, miners definitely do have an incentive to change Bitcoin's rules in their favor. It is only reasonably secure to use a lightweight node because most of the Bitcoin economy uses full nodes.

Therefore, it is critical for Bitcoin's survival that the great majority of the Bitcoin economy be backed by full nodes, not lightweight nodes. This is especially important for Bitcoin businesses, which have more economic weight. To contribute to Bitcoin's economic strength, you must actually use a full node for your real transactions (or use a lightweight node connected to a full node that you personally control). Just running a full node on a server somewhere does not contribute to Bitcoin's economic strength.

More details https://www.reddit.com/r/BitcoinBeginners/comments/3eq3y7/full_node_question/ctk4lnd

Downloading the entire blockchain is the most private way to operate a wallet. All other lightweight solutions leak information about which addresses are yours because they must query third-party servers. The Electrum servers will know which addresses belong to you and can link them together. Despite bloom filtering, SPV nodes based on BitcoinJ do not provide much privacy against nodes who connected directly to the wallet [1].

For some use cases, such privacy may not be required. But an important reason to run a full node and use it as a wallet is to get the full privacy benefits.

Lightweight nodes are sometimes able to be temporarily tricked into accepting transactions or blocks that are not actually valid. This could cause serious financial damage, especially for websites that automatically process Bitcoin transactions. Full nodes provide the maximum security possible, and so they should be used by all businesses, and also by regular users whenever doing so is convenient.

Full nodes may provide various services to other network participants (if the software is run with -listen=1 as is default). This is especially important for lightweight nodes.

These services include:

• Filtering transactions and blocks on behalf of lightweight nodes so that lightweight nodes do not need to download every transaction ever made on the network in order to find their own transactions.
• Serving historical full blocks to nodes that have been offline for a while.
• Transmitting new transactions from users to miners.
• Broadcasting new blocks from miners to other nodes.

For the most part, these services are only usefully performed by full nodes that are listening on port 8333. The more full nodes that accept incoming connections there are, the more users the Bitcoin network can support. Although if there is ever a shortage, lots of archival nodes can be easily created by cheaply renting VPS or AWS space.

Bitnodes ran a program to incentivize full node operators until the end of 2015.[2]

For Bitcoin Core:

• Bandwidth consumption can be reduced using this guide: https://btcinformation.org/en/full-node#reduce-traffic

• Requirement for disk space can be reduced using this guide: https://btcinformation.org/en/full-node#reduce-storage See also the release notes which explain pruning.

• This site has a nice predefined template for generating bitcoin config files https://jlopp.github.io/bitcoin-core-config-generator/

• Improve sync speed by increasing the dbcache value in configuration. This value controls how many megabytes of RAM to use for the database cache, increase it to as much as your hardware allows to reduce the disk operations and increase speed.

• To store the blockchain files on an external hard drive use -datadir. e.g. -datadir=/path/to/your/bitcoin/directory.

• Store the chainstate directory on an SSD drive to improve the speed.[3]
  • See Splitting the data directory

See Also: Running Bitcoin