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README.md

Channel tools

Index

This tool provides helper functions that can be used to rescue funds locked in lnd channels in case lnd itself cannot run properly anymore.

WARNING: This tool was specifically built for a certain rescue operation and might not be well-suited for your use case. Or not all edge cases for your needs are coded properly. Please look at the code to understand what it does before you use it for anything serious.

WARNING 2: This tool will query public block explorer APIs for some commands, your privacy might not be preserved. Use at your own risk or supply a private API URL with --apiurl.

Installation

The easiest way to install chantools is to download a pre-built binary for your operating system and architecture.

Example (make sure you always use the latest version!):

$ cd /tmp
$ wget -O chantools.tar.gz https://github.com/guggero/chantools/releases/download/v0.7.1/chantools-linux-amd64-v0.7.1.tar.gz
$ tar -zxvf chantools.tar.gz
$ sudo mv chantools-*/chantools /usr/local/bin/

Compile from source

If there isn't a pre-built binary for your operating system or architecture available or you want to build chantools from source for another reason, you need to make sure you have go 1.13.x (or later) and make installed and can then run the following commands:

git clone https://github.com/guggero/chantools.git
cd chantools
make install

Channel recovery scenario

The following flow chart shows the main recovery scenario this tool was built for. This scenario assumes that you do have access to the crashed node's seed, channel.backup file and some state of a channel.db file (perhaps from a file based backup or the recovered file from the crashed node).

rescue flow

Explanation:

  1. Node crashed: For some reason your lnd node crashed and isn't starting anymore. If you get errors similar to this, this or this, it is possible that a simple compaction (a full copy in safe mode) can solve your problem. See chantools compactdb.

    If that doesn't work and you need to continue the recovery, make sure you can at least extract the channel.backup file and if somehow possible any version of the channel.db from the node.

    Whatever you do, do never, ever replace your channel.db file with an old version (from a file based backup) and start your node that way. Read this explanation why that can lead to loss of funds.

  2. Rescue on-chain balance: To start the recovery process, we are going to re-create the node from scratch. To make sure we don't overwrite any old data in the process, make sure the old data directory of your node (usually .lnd in the user's home directory) is safely moved away (or the whole folder renamed) before continuing.
    To start the on-chain recovery, follow the sub step "Starting On-Chain Recovery" of this guide. Don't follow the whole guide, only this single chapter!

    This step is completed once the lncli getinfo command shows both "synced_to_chain": true and "synced_to_graph": true which can take several hours depending on the speed of your hardware. Do not be alarmed that the lncli getinfo command shows 0 channels. This is normal as we haven't started the off-chain recovery yet.

  3. Recover channels using SCB: Now that the node is fully synced, we can try to recover the channels using the Static Channel Backups (SCB). For this, you need a file called channel.backup. Simply run the command lncli restorechanbackup --multi_file <path-to-your-channel.backup>. This will take a while!. The command itself can take several minutes to complete, depending on the number of channels. The recovery can easily take a day or two as a lot of chain rescanning needs to happen. It is recommended to wait at least one full day. You can watch the progress with the lncli pendingchannels command. If the list is empty, congratulations, you've recovered all channels! If the list stays un-changed for several hours, it means not all channels could be restored using this method. One explanation can be found here.

  4. Install chantools: To try to recover the remaining channels, we are going to use chantools. Simply follow the installation instructions. The recovery can only be continued if you have access to some version of the crashed node's channel.db. This could be the latest state as recovered from the crashed file system, or a version from a regular file based backup. If you do not have any version of a channel DB, chantools won't be able to help with the recovery. See step 11 for some possible manual steps.

  5. Create copy of channel DB: To make sure we can read the channel DB, we are going to create a copy in safe mode (called compaction). Simply run

    chantools compactdb --sourcedb <recovered-channel.db> --destdb ./results/compacted.db

    We are going to assume that the compacted copy of the channel DB is located in ./results/compacted.db in the following commands.

  6. chantools summary: First, chantools needs to find out the state of each channel on chain. For this, a blockchain API (by default blockstream.info) is queried. The result will be written to a file called ./results/summary-yyyy-mm-dd.json. This result file will be needed for the next command.

    chantools --fromchanneldb ./results/compacted.db summary

  7. chantools rescueclosed: It is possible that by now the remote peers have force-closed some of the remaining channels. What we now do is try to find the private keys to sweep our balance of those channels. For this we need a shared secret which is called the commit_point and is changed whenever a channel is updated. We do have the latest known version of this point in the channel DB. The following command tries to find all private keys for channels that have been closed by the other party. The command needs to know what channels it is operating on, so we have to supply the summary-yyy-mm-dd.json created by the previous command:

    chantools --fromsummary ./results/<summary-file-created-in-last-step>.json rescueclosed --channeldb ./results/compacted.db

    This will create a new file called ./results/rescueclosed-yyyy-mm-dd.json which will contain any found private keys and will also be needed for the next command. Use bitcoind or Electrum Wallet to sweep all of the private keys.

  8. chantools forceclose: This command will now close all channels that chantools thinks are still open. This is achieved by publishing the latest known channel state of the channel.db file.
    Please read the full warning text of the forceclose command below as this command can put your funds at risk if the state in the channel DB is not the most recent one. This command should only be executed for channels where the remote peer is not online anymore.

    chantools --fromsummary ./results/<rescueclosed-file-created-in-last-step>.json forceclose --channeldb ./results/compacted.db --publish

    This will create a new file called ./results/forceclose-yyyy-mm-dd.json which will be needed for the next command.

  9. Wait for timelocks: The previous command closed the remaining open channels by publishing your node's state of the channel. By design of the Lightning Network, you now have to wait until the channel funds belonging to you are not time locked any longer. Depending on the size of the channel, you have to wait for somewhere between 144 and 2000 confirmations of the force-close transactions. Only continue with the next step after the channel with the highest csv_delay has reached that many confirmations of its closing transaction. You can check this by looking up each force closed channel transaction on a block explorer (like blockstream.info for example). Open the result JSON file of the last command (./results/forceclose-yyyy-mm-dd.json) and look up every TXID in "force_close" -> "txid" on the explorer. If the number of confirmations is equal to or greater to the value shown in "force_close" -> "csv_delay" for each of the channels, you can proceed.

  10. chantools sweeptimelock: Once all force-close transactions have reached the number of transactions as the csv_timeout in the JSON demands, these time locked funds can now be swept. Use the following command to sweep all the channel funds to an address of your wallet:

    chantools --fromsummary ./results/<forceclose-file-created-in-last-step>.json sweeptimelock --publish --sweepaddr <bech32-address-from-your-wallet>

  11. Manual intervention necessary: You got to this step because you either don't have a channel.db file or because chantools couldn't rescue all your node's channels. There are a few things you can try manually that have some chance of working:

  • Make sure you can connect to all nodes when restoring from SCB: It happens all the time that nodes change their IP addresses. When restoring from a static channel backup, your node tries to connect to the node using the IP address encoded in the backup file. If the address changed, the SCB restore process doesn't work. You can use block explorers like 1ml.com to try to find an IP address that is up-to-date. Just run lncli connect <node-pubkey>@<updated-ip-address>:<port> in the recovered lnd node from step 3 and wait a few hours to see if the channel is now being force closed by the remote node.
  • Find out who the node belongs to: Maybe you opened the channel with someone you know. Or maybe their node alias contains some information about who the node belongs to. If you can find out who operates the remote node, you can ask them to force-close the channel from your end. If the channel was opened with the option_static_remote_key, (lnd v0.8.0 and later), the funds can be swept by your node.

Seed and passphrase input

All commands that require the seed (and, if set, the seed's passphrase) offer three distinct possibilities to specify it:

  1. Enter manually on the terminal: This is the safest option as it makes sure that the seed isn't stored in the terminal's command history.
  2. Pass the extened master root key as parameter: This is added as an option for users who don't have the full seed anymore, possibly because they used lnd's --noseedbackup flag and extracted the xprv from the wallet database with the walletinfo command. Those users can specify the master root key by passing the --rootkey command line flag to each command that requires the seed.
  3. Use environment variables: This option makes it easy to automate usage of chantools by removing the need to type into the terminal. There are three environment variables that can be set to skip entering values through the terminal:
    • AEZEED_MNEMONIC: Specifies the 24 word lnd aezeed.
    • AEZEED_PASSPHRASE: Specifies the passphrase for the aezeed. If no passphrase was used during the creation of the seed, the special value AEZEED_PASSPHRASE="-" needs to be passed to indicate no passphrase should be used or read from the terminal.
    • WALLET_PASSWORD: Specifies the encryption password that is needed to access a wallet.db file. This is currently only used by the walletinfo command.

Example using environment variables:

# We add a space in front of each command to tell bash we don't want this
# command stored in the history.
$    export AEZEED_MNEMONIC="abandon able ... ... ..."
# We didn't set a passphrase for this example seed, we need to indicate this by
# passing in a single dash character.
$    export AEZEED_PASSPHRASE="-"
$ chantools showrootkey

2020-10-29 20:22:42.329 [INF] CHAN: chantools version v0.6.0 commit v0.6.0-3

Your BIP32 HD root key is: xprv9s21ZrQH1...

Command overview

This tool provides helper functions that can be used rescue
funds locked in lnd channels in case lnd itself cannot run properly anymore.
Complete documentation is available at https://github.com/guggero/chantools/.

Usage:
  chantools [command]

Available Commands:
  chanbackup          Create a channel.backup file from a channel database
  compactdb           Create a copy of a channel.db file in safe/read-only mode
  derivekey           Derive a key with a specific derivation path
  dropchannelgraph    Remove all graph related data from a channel DB
  dumpbackup          Dump the content of a channel.backup file
  dumpchannels        Dump all channel information from an lnd channel database
  filterbackup        Filter an lnd channel.backup file and remove certain channels
  fixoldbackup        Fixes an old channel.backup file that is affected by the lnd issue #3881 (unable to derive shachain root key)
  forceclose          Force-close the last state that is in the channel.db provided
  genimportscript     Generate a script containing the on-chain keys of an lnd wallet that can be imported into other software like bitcoind
  help                Help about any command
  migratedb           Apply all recent lnd channel database migrations
  removechannel       Remove a single channel from the given channel DB
  rescueclosed        Try finding the private keys for funds that are in outputs of remotely force-closed channels
  rescuefunding       Rescue funds locked in a funding multisig output that never resulted in a proper channel; this is the command the initiator of the channel needs to run
  showrootkey         Extract and show the BIP32 HD root key from the 24 word lnd aezeed
  signrescuefunding   Rescue funds locked in a funding multisig output that never resulted in a proper channel; this is the command the remote node (the non-initiator) of the channel needs to run
  summary             Compile a summary about the current state of channels
  sweeptimelock       Sweep the force-closed state after the time lock has expired
  sweeptimelockmanual Sweep the force-closed state of a single channel manually if only a channel backup file is available
  vanitygen           Generate a seed with a custom lnd node identity public key that starts with the given prefix
  walletinfo          Shows info about an lnd wallet.db file and optionally extracts the BIP32 HD root key

Flags:
  -h, --help      help for chantools
  -r, --regtest   Indicates if regtest parameters should be used
  -t, --testnet   Indicates if testnet parameters should be used

Use "chantools [command] --help" for more information about a command.

Commands

Detailed documentation for each sub command is available in the docs folder.

Quick access: