c-lightning: A specification compliant Lightning Network implementation in C
c-lightning is a lighweight, highly customizable and standard compliant implementation of the Lightning Network protocol.
- Getting Started
- Further Information
This implementation has been in production use on the Bitcoin mainnet since early 2018, with the launch of the Blockstream Store.
We recommend getting started by experimenting on
regtest), but the implementation is considered stable and can be safely used on mainnet.
Any help testing the implementation, reporting bugs, or helping with outstanding issues is very welcome. Don't hesitate to reach out to us on IRC at #lightning-dev @ freenode.net, #c-lightning @ freenode.net, or on the implementation-specific mailing list email@example.com, or on the Lightning Network-wide mailing list firstname.lastname@example.org.
c-lightning only works on Linux and Mac OS, and requires a locally (or remotely) running
bitcoind (version 0.16 or above) that is fully caught up with the network you're testing on.
prune=n option in
bitcoin.conf) is partially supported, see here for more details.
There are 4 supported installation options:
- Installation from the Ubuntu PPA
- Installation of a pre-compiled binary from the release page on Github
- Using one of the provided docker images on the Docker Hub
- Compiling the source code yourself as described in the installation documentation.
For the impatient here's the gist of it for Ubuntu:
sudo apt-get install -y software-properties-common sudo add-apt-repository -u ppa:bitcoin/bitcoin sudo add-apt-repository -u ppa:lightningnetwork/ppa sudo apt-get install bitcoind lightningd
If you want to experiment with
lightningd, there's a script to set
bitcoind regtest test network of two local lightning nodes,
which provides a convenient
To test with real bitcoin, you will need to have a local
bitcoind node running:
bitcoind has synchronized with the network.
Make sure that you do not have
walletbroadcast=0 in your
~/.bitcoin/bitcoin.conf, or you may run into trouble.
Notice that running
lightningd against a pruned node may cause some issues if not managed carefully, see below for more information.
You can start
lightningd with the following command:
lightningd --network=bitcoin --log-level=debug
This creates a
.lightning/ subdirectory in your home directory: see
man -l doc/lightningd.8 (or https://lightning.readthedocs.io/) for more runtime options.
Using The JSON-RPC Interface
You can use
lightning-cli help to print a table of RPC methods;
lightning-cli help <command>
will offer specific information on that command.
- newaddr: get a bitcoin address to deposit funds into your lightning node.
- listfunds: see where your funds are.
- connect: connect to another lightning node.
- fundchannel: create a channel to another connected node.
- invoice: create an invoice to get paid by another node.
- pay: pay someone else's invoice.
- plugin: commands to control extensions.
Care And Feeding Of Your New Lightning Node
Once you've started for the first time, there's a script called
contrib/bootstrap-node.sh which will connect you to other nodes on
the lightning network.
You can encrypt the BIP32 root seed (what is stored in
hsm_secret) by passing the
--encrypted-hsm startup argument. You can start
--encrypted-hsm on an already existing
lightning-dir (with a not encrypted
hsm_secret). If you pass that option, you will not be able to start
lightningd (with the same wallet) again without the password, so please beware with your password management. Also beware of not feeling too safe with an encrypted
hsm_secret: unlike for
bitcoind where the wallet encryption can restrict the usage of some RPC command,
lightningd always need to access keys from the wallet which is thus not locked (yet), even with an encrypted BIP32 master seed.
There are also numerous plugins available for c-lightning which add capabilities: in particular there's a collection at:
Including helpme which guides you through setting up your first channels and customizing your node.
You can also chat to other users at #c-lightning @ freenode.net; we are always happy to help you get started!
Opening A Channel
First you need to transfer some funds to
lightningd so that it can
open a channel:
# Returns an address <address> lightning-cli newaddr # Returns a transaction id <txid> bitcoin-cli sendtoaddress <address> <amount_in_bitcoins>
lightningd will register the funds once the transaction is confirmed.
You may need to generate a p2sh-segwit address if the faucet does not support bech32:
# Return a p2sh-segwit address lightning-cli newaddr p2sh-segwit
lightningd got funds by:
# Returns an array of on-chain funds. lightning-cli listfunds
lightningd has funds, we can connect to a node and open a channel.
Let's assume the remote node is accepting connections at
<port>, if not 9735) and has the node ID
lightning-cli connect <node_id> <ip> [<port>] lightning-cli fundchannel <node_id> <amount_in_satoshis>
This opens a connection and, on top of that connection, then opens
The funding transaction needs 3 confirmation in order for the channel to be usable, and 6 to be announced for others to use.
You can check the status of the channel using
lightning-cli listpeers, which after 3 confirmations (1 on testnet) should say that
CHANNELD_NORMAL; after 6 confirmations you can use
lightning-cli listchannels to verify that the
public field is now
Sending and Receiving Payments
Payments in Lightning are invoice based.
The recipient creates an invoice with the expected
"any" for a donation), a unique
<label> and a
<description> the payer will see:
lightning-cli invoice <amount> <label> <description>
This returns some internal details, and a standard invoice string called
bolt11 (named after the BOLT #11 lightning spec).
The sender can feed this
bolt11 string to the
decodepay command to see what it is, and pay it simply using the
lightning-cli pay <bolt11>
Note that there are lower-level interfaces (and more options to these interfaces) for more sophisticated use.
lightningd can be configured either by passing options via the command line, or via a configuration file.
Command line options will always override the values in the configuration file.
To use a configuration file, create a file named
config within your lightning directory
man -l doc/lightningd-config.5.
c-lightning requires JSON-RPC access to a fully synchronized
bitcoind in order to synchronize with the Bitcoin network.
Access to ZeroMQ is not required and
bitcoind does not need to be run with
txindex like other implementations.
The lightning daemon will poll
bitcoind for new blocks that it hasn't processed yet, thus synchronizing itself with
bitcoind prunes a block that c-lightning has not processed yet, e.g., c-lightning was not running for a prolonged period, then
bitcoind will not be able to serve the missing blocks, hence c-lightning will not be able to synchronize anymore and will be stuck.
In order to avoid this situation you should be monitoring the gap between c-lightning's blockheight using
lightning-cli getinfo and
bitcoind's blockheight using
If the two blockheights drift apart it might be necessary to intervene.
Developers wishing to contribute should start with the developer guide here.
You should also configure with
--enable-developer to get additional checks and options.