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Updated on September 23, 2021

# Weak subjectivity

The weak subjectivity period refers to how far behind the chain head a node can be before ⅓ of validators may have exited since the node was last in sync.

For example, if ⅓ of validators withdraw their stake and continue signing blocks and attestations, they can form a chain which conflicts with the finalised state. If your node is far enough behind the chain head not to be aware that they’ve withdrawn their funds, these validators can act dishonestly and continue feeding you blocks to lead you down the wrong chain.

Note

If a node is aware that a validator has withdrawn its funds, the node will reject the validator’s attestations.

Teku provides two methods to safely sync a node that’s been offline for an extended period.

1. Use --ws-checkpoint to supply a weak subjectivity checkpoint from which a node can securely update its view of the current state.
2. Use --initial-state to supply an SSZ encoded state file from which to sync.

Tip

The BeaconScan chain explorer provides the most recent weak subjectivity checkpoint from which to safely update your node’s view of the current state.

Use the /eth/v2/debug/beacon/states/<state_id> API on an updated node to download a recent finalized state as an SSZ encoded state file.

Questions or feedback? You can discuss issues and obtain free support on Teku Discord channel.