Disaster

liongrass / August 2023 (334 Words, 2 Minutes)

Disaster Preparation

In this short session, we are going to learn how to prepare for a disaster, meaning we can’t start our node, or lose access to it.

Useful resources:

• Disaster Recovery
• Voltage Recovery

Understanding disaster

A disaster refers to the worst possible situation when running a Lightning node: The node won’t start due to database or file system corruption, loss of data or loss of the entire node.

The most likely scenarios that could lead to disaster:

• We forget to pay our Lunanode bill and our node gets deleted
• A short circuit at home fries our node
• Our filesystem gets corrupted (almost guaranteed to happen with an SD card, and will eventually happen to every HDD)
• Error while migrating a node

To mitigate these problems, we can:

• Deposit enough sats on time
• Always use proper power supplies (a thick heavy brick somewhere along the cable is a good sign)
• Use quality SSDs, possibly with separate partitions or even RAID
• Exercise caution when migrating our node

Preparing for disaster

The Seed

Always back up your seed, ideally with a pencil on a piece of paper. Keep this paper somewhere dry and safe.

Static channel backup

The static channel backup, or channel.backup is located in ~/.lnd/data/chain/bitcoin/mainnet. It’s not an actual backup, as it doesn’t allow us to revive our channels and cannot be used to migrate channels. Instead, it functions as an “emergency distress beacon” to our peers. The file contains information about our channels, their channel points and our peers. Once we activate this file, our node will send a distress signal to its peers, urging them to force close all channels.

This file only works for peers that are online and reachable.

Everytime we open a new channel, the file is updated.

We can also grab the file and its contents from the command line.

lncli exportchanbackup --all

This returns the following file:

{
    "single_chan_backups": {
        "chan_backups": [
        ]
    },
    "multi_chan_backup": {
        "chan_points": [
        ],
        "multi_chan_backup": "c3aabf4fe30ccd061f24263166ee99183aa40f8dc8900f511b4538f536bb50733dac259c5004da5e8c6d867656"
    }
}

We can save it in a text file on our personal computer. Ideally we repeat this action everytime we open a channel.

We can verify a channel backup with the command:

lncli verifychanbackup --multi_file ~/.lnd/data/chain/bitcoin/mainnet/channel.backup

It should return simple empty brackets on success.

{

}

From our personal machine, we can also use the scp utlity to copy the file directly to our machine:

scp ubuntu@<your nodes ip>:/home/ubuntu/.lnd/data/chain/bitcoin/mainnet/channel.backup ~/Downloads

We can do this everytime we open a channel!

Channel Database

While the channel database (channel.db) is generally not suitable for recovery, it might help us in some rare situations where the peer is unavailable.

If you do suffer from a catastrophic failure of your node, never delete your data! Keep as much data as you can, especially anything in the .lnd directory.