Channel tools

Index

• Installation
• Channel recovery scenario
• Seed and passphrase input
• Command overview
• Commands

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/lightninglabs/chantools/releases/download/v0.11.3/chantools-linux-amd64-v0.11.3.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 1.19.x (or later) and make installed and can then run the following commands:

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

When should I use what command?

This list contains a list of scenarios that users seem to run into sometimes.

Before you start running any chantools command, you MUST read the "What should I NEVER do?" section below!

Scenarios:

• My node/disk/database crashed and I only have the seed and channel.backup file.

  This is the "normal" recovery scenario for which you don't need chantools. Just follow the lnd recovery guide. All channels will be closed to recover funds, so you should still try to avoid This scenario. You only need chantools if you had zombie channels or a channel that did not confirm in time (see below).

• My node/disk/database crashed and I only have the seed.

  This is very bad and recovery will take manual steps and might not be successful for private channels. If you do not have any data left from your node, you need to follow the chantools fakechanbackup command help text. If you do have an old version of your channel.db file, DO NOT UNDER ANY CIRCUMSTANCES start your node with it. Instead, try to extract a channel.backup from it using the chantools chanbackup command. If that is successful, follow the steps in the lnd recovery guide. This will not cover new channels opened after the backup of the channel.db file was created. You might still need to create the fake channel backup.

• I suspect my channel.db file to be corrupt.

  This can happen due to unclean shutdowns or power outages. Try running chantools compactdb. If there are NO ERRORS during the execution of that command, things should be back to normal, and you can continue running your node. If you get errors, you should probably follow the recovery scenario described below to avoid future issues. This will close all channels, however.

• I don't have a channel.backup file but all my peers force closed my channels, why don't I see the funds with just my seed?

  When a channel is force closed by the remote party, the funds don't automatically go to a normal on-chain address. You need to sweep those funds using the chantools sweepremoteclosed command.

• My channel peer is online, but they don't force close a channel when using a channel.backup file.

  This can have many reasons. Often it means the channels is a legacy channel type (not an anchor output channel) and the force close transaction the peer has doesn't have enough fees to make it into the mempool. In that case waiting for an empty mempool might be the only option. Another reason might be that the peer is a CLN node with a specific version that doesn't react to force close requests normally. You can use the chantools triggerforceclose command in that case (ONLY works with CLN peers of a certain version).

What should I NEVER do?

• You should never panic. There are extremely few situations in which doing nothing makes things worse. On the contrary, most cases where users actually lost funds it was due to them running commands they did not understand in a rush of panic. So stay calm, try to find out what the reason for the problem is, ask for help (see Slack, lnd discussions) or use Google. Create a backup of all your files in the lnd data directory (just in case, but never start a node from a file based backup) before running any command. Also read the lnd Operational Safety Guidelines.
• Whatever you might read in any issue, you should never use lncli abandonchannel on a channel that was confirmed on chain. Even if you have an SCB (Static Channel Backup, unfortunately poorly named) file (channel.backup) or export from lncli exportchanbackup. Those files DO NOT contain enough information to close a channel if your peer does not have the channel data either (which might happen if the channel took longer than 2 weeks to confirm). If the channel confirmed on chain, you need to force close it from your node if it does not operate normally. Running abandonchannel deletes the information needed to be able to force close.
• When running Umbrel, NEVER just uninstall the Lightning App when encountering a problem. Uninstalling the app deletes important data that might be needed for recovery in edge cases. The channel backup (SCB) in the cloud does NOT cover "expired" channels (channels that took longer than 2 weeks to confirm) or zombie channels.
• The term "backup" in SCB (Static Channel Backup) or the channel.backup file or the output of lncli exportchanbackup is not optimal as it implies the channels can be fully restored or brought back to an operational state. But the content of those files are for absolute emergencies only. Channels are always closed when using such a file (by asking the remote peer to issue their latest force close transaction they have). So chain fees occur. And there are some edge cases where funds are not covered by those files, for example when a channel funding transaction is not confirmed in time. Or for channels where the peer is no longer online. So deleting your lnd data directory should never ever be something to be done lightly (see Umbrel above).

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).

Following this guide will help you get your channel funds back! The channels themselves can't be restored to work normally unless step 1 is successful ( compacting the DB).

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][2]. 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.][1]

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.
   
   If you get the error non-mandatory-script-verify-flag (Signature must be zero for failed CHECK(MULTI)SIG operation), you might be affected by an old bug of lnd that was fixed in the meantime. But it means the signature in the force-close transaction is invalid and needs to be fixed. There is a guide on how to do exactly that here.

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 their 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.

12. Use Zombie Channel Recovery Matcher: As a final, last resort, you can go to node-recovery.com and register your node's ID for being matched up against other nodes with the same problem.
    
    Once you were contacted with a match, follow the instructions on the Zombie Channel Recovery Guide page.
    
    If you know the peer of a zombie channel and have a way to contact them, you can also skip the registration/matching process and create your own match file.

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...

Are my funds safe?

Some commands require the seed. But your seed will never leave your computer.

Most commands don't require an internet connection: you can and should run them on a computer with a firewall that blocks outgoing connections.

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/lightninglabs/chantools/.

Usage:
  chantools [command]

Available Commands:
  chanbackup          Create a channel.backup file from a channel database
  closepoolaccount    Tries to close a Pool account that has expired
  compactdb           Create a copy of a channel.db file in safe/read-only mode
  deletepayments      Remove all (failed) payments from a channel DB
  derivekey           Derive a key with a specific derivation path
  doublespendinputs   Tries to double spend the given inputs by deriving the private for the address and sweeping the funds to the given address. This can only be used with inputs that belong to an lnd wallet.
  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
  fakechanbackup      Fake a channel backup file to attempt fund recovery
  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
  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
  rescuetweakedkey    Attempt to rescue funds locked in an address with a key that was affected by a specific bug in lnd
  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
  sweepremoteclosed   Go through all the addresses that could have funds of channels that were force-closed by the remote party. A public block explorer is queried for each address and if any balance is found, all funds are swept to a given address
  triggerforceclose   Connect to a peer and send a custom message to trigger a force close of the specified channel
  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
  zombierecovery      Try rescuing funds stuck in channels with zombie nodes
  help                Help about any command

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.

The following table provides quick access to each command's documentation. Legend:

• 📝 This command requires the seed to be entered (see seed and passphrase input).
• ⚠️ Should not be used unless no other option exists, can lead to malfunction of the node.
• 💀 Danger of loss of funds, only use when instructed to.
• 📌 Command was created for a very specific version or use case and most likely does not apply to 99.9% of users