A user-activated soft fork (UASF) is a type of soft fork in the Bitcoin network that is activated by users and nodes, rather than miners. In a soft fork, new rules are added to the protocol, but old nodes that do not implement the new rules will still be able to communicate with the network and process transactions. However, if a user or node wants to take advantage of the new features introduced by the soft fork, they will need to upgrade their software.
A UASF is activated when a majority of users and nodes signal their support for the new rules. This is done by setting a flag in their software that indicates that they will only accept blocks that follow the new rules. Once a majority of users and nodes have signaled their support, the soft fork is activated and all nodes on the network must follow the new rules.
Miners are not required to follow the rules of a UASF, but if they want to continue to mine blocks that are accepted by the network, they will need to upgrade their software. If a miner continues to mine blocks that do not follow the new rules, their blocks will be rejected by the network and they will not receive any block rewards.
The main advantage of a UASF is that it allows users and nodes to take control of the activation of soft forks. This is in contrast to miner-activated soft forks, which are activated by miners. Miner-activated soft forks can be controversial, as miners have a financial incentive to delay or prevent the activation of soft forks that they do not support.
The main disadvantage of a UASF is that it can be more difficult to activate than a miner-activated soft fork. This is because users and nodes need to coordinate their efforts in order to signal their support for the new rules. However, if a UASF is successful, it can be a more secure and democratic way to activate soft forks in the Bitcoin network.
The first UASF was activated on August 1, 2017, to activate the Segregated Witness (SegWit) soft fork. SegWit is a change to the Bitcoin protocol that improves the scalability of the network. The UASF was successful in activating SegWit, and it is now a permanent part of the Bitcoin protocol.
UASFs have the potential to be a powerful tool for users and nodes to control the evolution of the Bitcoin network. By giving users and nodes a say in the activation of soft forks, UASFs can help to ensure that the network remains decentralized and democratic.