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doc: start an FAQ
This regroups questions (frequently) seen in Github issues, on IRC, and also some I've been asked in face to face. Changelog-Added: doc: An FAQ was added, accessible at https://lightning.readthedocs.io/FAQ.html Christian wrote the block chain rescaning paragraph. Lisa corrected my poor english grammar. Co-Authored-by: Christian Decker <decker.christian@gmail.com> Co-Authored-by: Lisa Neigut <niftynei@gmail.com>
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darosior
neil saitug
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@ -11,6 +11,7 @@ c-lightning is a lightweight, highly customizable and [standard compliant][std]
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* [Sending and Receiving Payments](#sending-and-receiving-payments)
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* [Configuration File](#configuration-file)
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* [Further Information](#further-information)
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* [FAQ](doc/FAQ.md)
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* [Pruning](#pruning)
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* [HD wallet encryption](#hd-wallet-encryption)
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* [Developers](#developers)
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164
doc/FAQ.md
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164
doc/FAQ.md
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@ -0,0 +1,164 @@
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# FAQ
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## Table of contents
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- [General questions](#general-questions)
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- [Loss of {funds / data}](#loss)
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## General questions
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### I don't know where to start, help me !
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There is a C-lightning plugin specifically for this purpose, it's called
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[`helpme`](https://github.com/lightningd/plugins/tree/master/helpme).
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Assuming you have followed the [installation steps](INSTALL.md), have `lightningd`
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up and running, and `lightning-cli` in your `$PATH` you can start the plugin like so:
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```
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# Clone the plugins repository
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git clone https://github.com/lightningd/plugins
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# Make sure the helpme plugin is executable (git should have already handled this)
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chmod +x plugins/helpme/helpme.py
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# Install its dependencies (there is only one actually)
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pip3 install --user -r plugins/helpme/requirements.txt
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# Then just start it :)
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lightning-cli plugin start $PWD/plugins/helpme/helpme.py
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```
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The plugin registers a new command `helpme` which will guide you through the main
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components of C-lightning:
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```
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lightning-cli helpme
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```
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### How to get the balance of each channel ?
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You can use the `listfunds` command and take a ratio of `our_amount_msat` over
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`amount_msat`. Note that this doesn't account for the [channel reserve](https://github.com/lightningnetwork/lightning-rfc/blob/master/02-peer-protocol.md#rationale).
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A better option is to use the [`summary` plugin](https://github.com/lightningd/plugins/tree/master/summary)
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which nicely displays channel balances, along with other useful channel informations.
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### My channel which only tries the passed in route is in state `STATE`, what does that mean ?
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See the [listpeers command manpage](https://lightning.readthedocs.io/lightning-listpeers.7.html#return-value).
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### My payment is failing / all my payments are failing, why ?
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There are many reasons for a payment failure. The most common one is a
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[failure](https://github.com/lightningnetwork/lightning-rfc/blob/master/04-onion-routing.md#failure-messages)
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along the route from you to the payee.
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The best (and most common) solution to a route failure problem is to open more channels,
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which should increase the available routes to the recipient and lower the probability of a failure.
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Hint: use the [`pay`](lightning-pay.7.md) command which is will iterate through trying all possible routes,
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instead of the low-level `sendpay` command which only tries the passed in route.
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### How can I receive payments ?
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In order to receive payments you need inbound liquidity. You get inbound liquidity when
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another node opens a channel to you or by successfully completing a payment out through a channel you opened.
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If you need a lot of inbound liquidity, you can use a service that trustlessly swaps on-chain Bitcoin
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for Lightning channel capacity.
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There are a few online service providers that will create channels to you.
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A few of them charge fees for this service.
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Note that if you already have a channel open to them, you'll need to close it before requesting another channel.
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### Are there any issues if my node changes its IP address? What happens to the channels if it does?
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There is no risk to your channels if your IP address changes.
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However, be sure to change your announced address (or [setup a TOR hidden service](TOR.md))
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in your config so that others can establish connections at your new address !
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### Can I have two hosts with the same public key and different IP addresses, both online and operating at the same time?
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No.
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### Can I use a single `bitcoind` for multiple `lightningd` ?
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Yes. All `bitcoind` calls are handled by the bundled `bcli` plugin. `lightningd` does not use
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`bitcoind`'s wallet. While on the topic, `lightningd` does not require the `-txindex` option on `bitcoind`.
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If you use a single `bitcoind` for multiple `lightningd`'s, be sure to raise the `bitcoind`
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max RPC thread limit (`-rpcthreads`), each `lightningd` can use up to 4 threads, which is
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the default `bitcoind` max.
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### Can I use C-lightning on mobile ?
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#### Remote control
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[Spark-wallet](https://github.com/shesek/spark-wallet/) is the most popular remote control
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HTTP server for `lightningd`.
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**Use it [behind tor](https://github.com/shesek/spark-wallet/blob/master/doc/onion.md)**.
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#### `lightningd` on Android
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Effort has been made to get `lightningd` running on Android,
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[see issue #3484](https://github.com/ElementsProject/lightning/issues/3484). Currently unusable.
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### How to "backup my wallet" ?
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As a Bitcoin user, one may be familiar with a file or a seed (or some mnemonics) from which
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it can recover all its funds.
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C-lightning has an internal bitcoin wallet, which you can use to make "on-chain"
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transactions, (see [withdraw](https://lightning.readthedocs.io/lightning-withdraw.7.html).
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These on-chain funds are backed up via the HD wallet seed, stored in byte-form in `hsm_secret`.
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and which you can backup thanks to a seed stored in the `hsm_secret`.
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`lightningd` also stores information for funds locked in Lightning Network channels, which are stored
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in a database. This database is required for on-going channel updates as well as channel closure.
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There is no single-seed backup for funds locked in channels.
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While crucial for node operation, snapshot-style backups of the `lightningd` database is **discouraged**,
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as _any_ loss of state may result in permanent loss of funds.
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See the [penalty mechanism](https://github.com/lightningnetwork/lightning-rfc/blob/master/05-onchain.md#revoked-transaction-close-handling)
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for more information on why any amount of state-loss results in fund loss.
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Real-time database replication is the recommended approach to backing up node data.
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Tools for replication are currently in active development, using the `db_write`
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[plugin hook](https://lightning.readthedocs.io/PLUGINS.html#db-write).
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## Loss
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### Rescanning the block chain for lost utxos
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There are 3 types of 'rescans' you can make:
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- `rescanblockchain`: A `bitcoind` RPC call which rescans the blockchain
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starting at the given height. This does not have an effect on c-lightning
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as `lightningd` tracks all block and wallet data independently.
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- `--rescan=depth`: A `lightningd` configuration flag. This flag is read at node startup
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and tells lightningd at what depth from current blockheight to rebuild its internal state.
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(You can specify an exact block to start scanning from, instead of depth from current height,
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by using a negative number.)
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- `dev-rescan-outputs`: A `lightningd` RPC call. Only available if your node has been
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configured and built in DEVELOPER mode (i.e. `./configure --enable-developer`) This
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will sync the state for known UTXOs in the `lightningd` wallet with `bitcoind`.
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As it only operates on outputs already seen on chain by the `lightningd` internal
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wallet, this will not find missing wallet funds.
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### Database corruption / channel state lost
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If you lose data (likely corrupted `lightningd.sqlite3`) about a channel __with `option_static_remotekey` enabled__,
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you can wait for your peer to unilateraly close the channel, then use `tools/hsmtool` with the
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`guesstoremote` command to attempt to recover your funds from the peer's published unilateral close transaction.
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If `option_static_remotekey` was not enabled, you're probably out of luck. The keys for your funds in your peer's
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unilateral close transaction are derived from information you lost. Fortunately, since version `0.7.3` channels
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are created with `option_static_remotekey` by default if your peer supports it.
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Which is to say that channels created after block [598000](https://blockstream.info/block/0000000000000000000dd93b8fb5c622b9c903bf6f921ef48e266f0ead7faedb)
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(short channel id starting with > 598000) have a high chance of supporting `option_static_remotekey`.
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You can verify it using the `features` field from the [`listpeers` command](https://lightning.readthedocs.io/lightning-listpeers.7.html)'s result.
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Here is an example in Python checking if [one of the `option_static_remotekey` bits](https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md) is set in the negotiated features corresponding to `0x02aaa2`:
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```python
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>>> bool(0x02aaa2 & ((1 << 12) | (1 << 13)))
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True
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```
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@ -7,6 +7,7 @@ c-lightning Documentation
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INSTALL.md
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TOR.md
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FAQ <FAQ.md>
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.. toctree::
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:maxdepth: 2
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