This implementation has been in production use on the Bitcoin mainnet since early 2018, with the launch of the [Blockstream Store][blockstream-store-blog].
We recommend getting started by experimenting on `testnet` (or `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][irc1], [#c-lightning @ freenode.net][irc2], or on the implementation-specific mailing list [c-lightning@lists.ozlabs.org][ml1], or on the Lightning Network-wide mailing list [lightning-dev@lists.linuxfoundation.org][ml2].
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 running on, and relays transactions (ie with `blocksonly=0`).
This creates a `.lightning/` subdirectory in your home directory: see `man -l doc/lightningd.8` (or https://lightning.readthedocs.io/) for more runtime options.
c-lightning exposes a [JSON-RPC 2.0][jsonrpcspec] interface over a Unix Domain socket; the `lightning-cli` tool can be used to access it, or there is a [python client library](contrib/pylightning).
You can use `lightning-cli help` to print a table of RPC methods; `lightning-cli help <command>`
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 `state` is `CHANNELD_NORMAL`; after 6 confirmations you can use `lightning-cli listchannels` to verify that the `public` field is now `true`.
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`.
If `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 `bitcoin-cli getblockchaininfo`.
If the two blockheights drift apart it might be necessary to intervene.
You can encrypt the `hsm_secret` content (which is used to derive the HD wallet's master key) by passing the `--encrypted-hsm` startup argument, or by using the `hsmtool` (which you can find in the `tool/` directory at the root of this repo) with the `encrypt` method. You can unencrypt an encrypted `hsm_secret` using the `hsmtool` with the `decrypt` method.
If you encrypt your `hsm_secret`, you will have to pass the `--encrypted-hsm` startup option to `lightningd`. Once your `hsm_secret` is encrypted, you __will not__ be able to access your funds without your 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.
