How to revert a bricked chain due to bad setCode

Question

I upgraded a chain that uses Grandpa/Aura with code for instant seal by mistake. I believe it may be possible to revert some blocks:

https://github.com/paritytech/substrate/pull/1479

But cannot find any documentation on how to do this. It is also asked here: How to unbrick a Substrate Chain? --revert?

But no answer for how to use --revert is given.

Answer 1

You can use the revert command to revert unfinalized blocks. If you need to revert finalized blocks then I suggest you do the following:

• Assuming you want to revert to block #42;
• Add the hash of block #43 to the chain spec under badBlocks (example: https://raw.githubusercontent.com/paritytech/polkadot/a4931d93388688af2e39e1aca77a6dcefd4bbd10/node/service/chain-specs/kusama.json);
• Sync a node from scratch and it should stop importing blocks after #42 (since #43 is blacklisted it will fail to import);
• You can now deploy this database to other validators and they should start authoring (and finalizing on top of #42). Alternatively you can also just resync using the new chain spec;
• Since you are reverting finality all clients on the network will need to resync (using the new chainspec with badBlocks populated).

Answer 2

I figured out how to revert some blocks:

./{chain executable} revert --base-path /home/ubuntu/chains --chain {chain name}--keep-blocks 351284 --pruning archive

For options:

./{chain executable} revert --help