# Using Tendermint

This is a guide to using the `tendermint` program from the command line.
It assumes only that you have the `tendermint` binary installed and have
some rudimentary idea of what Tendermint and ABCI are.

You can see the help menu with `tendermint --help`, and the version
number with `tendermint version`.

## Directory Root

The default directory for blockchain data is `~/.tendermint`. Override
this by setting the `TMHOME` environment variable.

## Initialize

Initialize the root directory by running:

```
tendermint init
```

This will create a new private key (`priv_validator.json`), and a
genesis file (`genesis.json`) containing the associated public key, in
`$TMHOME/config`. This is all that's necessary to run a local testnet
with one validator.

For more elaborate initialization, see the tesnet command:

```
tendermint testnet --help
```

## Run

To run a Tendermint node, use

```
tendermint node
```

By default, Tendermint will try to connect to an ABCI application on
[127.0.0.1:26658](127.0.0.1:26658). If you have the `kvstore` ABCI app
installed, run it in another window. If you don't, kill Tendermint and
run an in-process version of the `kvstore` app:

```
tendermint node --proxy_app=kvstore
```

After a few seconds you should see blocks start streaming in. Note that
blocks are produced regularly, even if there are no transactions. See
_No Empty Blocks_, below, to modify this setting.

Tendermint supports in-process versions of the `counter`, `kvstore` and
`nil` apps that ship as examples with `abci-cli`. It's easy to compile
your own app in-process with Tendermint if it's written in Go. If your
app is not written in Go, simply run it in another process, and use the
`--proxy_app` flag to specify the address of the socket it is listening
on, for instance:

```
tendermint node --proxy_app=/var/run/abci.sock
```

## Transactions

To send a transaction, use `curl` to make requests to the Tendermint RPC
server, for example:

```
curl http://localhost:26657/broadcast_tx_commit?tx=\"abcd\"
```

We can see the chain's status at the `/status` end-point:

```
curl http://localhost:26657/status | json_pp
```

and the `latest_app_hash` in particular:

```
curl http://localhost:26657/status | json_pp | grep latest_app_hash
```

Visit http://localhost:26657> in your browser to see the list of other
endpoints. Some take no arguments (like `/status`), while others specify
the argument name and use `_` as a placeholder.

### Formatting

The following nuances when sending/formatting transactions should be
taken into account:

With `GET`:

To send a UTF8 string byte array, quote the value of the tx pramater:

```
curl 'http://localhost:26657/broadcast_tx_commit?tx="hello"'
```

which sends a 5 byte transaction: "h e l l o" \[68 65 6c 6c 6f\].

Note the URL must be wrapped with single quoes, else bash will ignore
the double quotes. To avoid the single quotes, escape the double quotes:

```
curl http://localhost:26657/broadcast_tx_commit?tx=\"hello\"
```

Using a special character:

```
curl 'http://localhost:26657/broadcast_tx_commit?tx="€5"'
```

sends a 4 byte transaction: "€5" (UTF8) \[e2 82 ac 35\].

To send as raw hex, omit quotes AND prefix the hex string with `0x`:

```
curl http://localhost:26657/broadcast_tx_commit?tx=0x01020304
```

which sends a 4 byte transaction: \[01 02 03 04\].

With `POST` (using `json`), the raw hex must be `base64` encoded:

```
curl --data-binary '{"jsonrpc":"2.0","id":"anything","method":"broadcast_tx_commit","params": {"tx": "AQIDBA=="}}' -H 'content-type:text/plain;' http://localhost:26657
```

which sends the same 4 byte transaction: \[01 02 03 04\].

Note that raw hex cannot be used in `POST` transactions.

## Reset

**WARNING: UNSAFE** Only do this in development and only if you can
afford to lose all blockchain data!

To reset a blockchain, stop the node, remove the `~/.tendermint/data`
directory and run

```
tendermint unsafe_reset_priv_validator
```

This final step is necessary to reset the `priv_validator.json`, which
otherwise prevents you from making conflicting votes in the consensus
(something that could get you in trouble if you do it on a real
blockchain). If you don't reset the `priv_validator.json`, your fresh
new blockchain will not make any blocks.

## Configuration

Tendermint uses a `config.toml` for configuration. For details, see [the
config specification](./specification/configuration.md).

Notable options include the socket address of the application
(`proxy_app`), the listening address of the Tendermint peer
(`p2p.laddr`), and the listening address of the RPC server
(`rpc.laddr`).

Some fields from the config file can be overwritten with flags.

## No Empty Blocks

This much requested feature was implemented in version 0.10.3. While the
default behaviour of `tendermint` is still to create blocks
approximately once per second, it is possible to disable empty blocks or
set a block creation interval. In the former case, blocks will be
created when there are new transactions or when the AppHash changes.

To configure Tendermint to not produce empty blocks unless there are
transactions or the app hash changes, run Tendermint with this
additional flag:

```
tendermint node --consensus.create_empty_blocks=false
```

or set the configuration via the `config.toml` file:

```
[consensus]
create_empty_blocks = false
```

Remember: because the default is to _create empty blocks_, avoiding
empty blocks requires the config option to be set to `false`.

The block interval setting allows for a delay (in seconds) between the
creation of each new empty block. It is set via the `config.toml`:

```
[consensus]
create_empty_blocks_interval = 5
```

With this setting, empty blocks will be produced every 5s if no block
has been produced otherwise, regardless of the value of
`create_empty_blocks`.

## Broadcast API

Earlier, we used the `broadcast_tx_commit` endpoint to send a
transaction. When a transaction is sent to a Tendermint node, it will
run via `CheckTx` against the application. If it passes `CheckTx`, it
will be included in the mempool, broadcasted to other peers, and
eventually included in a block.

Since there are multiple phases to processing a transaction, we offer
multiple endpoints to broadcast a transaction:

```
/broadcast_tx_async
/broadcast_tx_sync
/broadcast_tx_commit
```

These correspond to no-processing, processing through the mempool, and
processing through a block, respectively. That is, `broadcast_tx_async`,
will return right away without waiting to hear if the transaction is
even valid, while `broadcast_tx_sync` will return with the result of
running the transaction through `CheckTx`. Using `broadcast_tx_commit`
will wait until the transaction is committed in a block or until some
timeout is reached, but will return right away if the transaction does
not pass `CheckTx`. The return value for `broadcast_tx_commit` includes
two fields, `check_tx` and `deliver_tx`, pertaining to the result of
running the transaction through those ABCI messages.

The benefit of using `broadcast_tx_commit` is that the request returns
after the transaction is committed (i.e. included in a block), but that
can take on the order of a second. For a quick result, use
`broadcast_tx_sync`, but the transaction will not be committed until
later, and by that point its effect on the state may change.

## Tendermint Networks

When `tendermint init` is run, both a `genesis.json` and
`priv_validator.json` are created in `~/.tendermint/config`. The
`genesis.json` might look like:

```
{
  "validators" : [
    {
      "pub_key" : {
        "value" : "h3hk+QE8c6QLTySp8TcfzclJw/BG79ziGB/pIA+DfPE=",
        "type" : "tendermint/PubKeyEd25519"
      },
      "power" : 10,
      "name" : ""
    }
  ],
  "app_hash" : "",
  "chain_id" : "test-chain-rDlYSN",
  "genesis_time" : "0001-01-01T00:00:00Z"
}
```

And the `priv_validator.json`:

```
{
  "last_step" : 0,
  "last_round" : "0",
  "address" : "B788DEDE4F50AD8BC9462DE76741CCAFF87D51E2",
  "pub_key" : {
    "value" : "h3hk+QE8c6QLTySp8TcfzclJw/BG79ziGB/pIA+DfPE=",
    "type" : "tendermint/PubKeyEd25519"
  },
  "last_height" : "0",
  "priv_key" : {
    "value" : "JPivl82x+LfVkp8i3ztoTjY6c6GJ4pBxQexErOCyhwqHeGT5ATxzpAtPJKnxNx/NyUnD8Ebv3OIYH+kgD4N88Q==",
    "type" : "tendermint/PrivKeyEd25519"
  }
}
```

The `priv_validator.json` actually contains a private key, and should
thus be kept absolutely secret; for now we work with the plain text.
Note the `last_` fields, which are used to prevent us from signing
conflicting messages.

Note also that the `pub_key` (the public key) in the
`priv_validator.json` is also present in the `genesis.json`.

The genesis file contains the list of public keys which may participate
in the consensus, and their corresponding voting power. Greater than 2/3
of the voting power must be active (i.e. the corresponding private keys
must be producing signatures) for the consensus to make progress. In our
case, the genesis file contains the public key of our
`priv_validator.json`, so a Tendermint node started with the default
root directory will be able to make progress. Voting power uses an int64
but must be positive, thus the range is: 0 through 9223372036854775807.
Because of how the current proposer selection algorithm works, we do not
recommend having voting powers greater than 10\^12 (ie. 1 trillion) (see
[Proposals section of Byzantine Consensus
Algorithm](./specification/byzantine-consensus-algorithm.md#proposals)
for details).

If we want to add more nodes to the network, we have two choices: we can
add a new validator node, who will also participate in the consensus by
proposing blocks and voting on them, or we can add a new non-validator
node, who will not participate directly, but will verify and keep up
with the consensus protocol.

### Peers

#### Seed

A seed node is a node who relays the addresses of other peers which they know
of. These nodes constantly crawl the network to try to get more peers. The
addresses which the seed node relays get saved into a local address book. Once
these are in the address book, you will connect to those addresses directly.
Basically the seed nodes job is just to relay everyones addresses. You won't
connect to seed nodes once you have received enough addresses, so typically you
only need them on the first start. The seed node will immediately disconnect
from you after sending you some addresses.

#### Persistent Peer

Persistent peers are people you want to be constantly connected with. If you
disconnect you will try to connect directly back to them as opposed to using
another address from the address book. On restarts you will always try to
connect to these peers regardless of the size of your address book.

All peers relay peers they know of by default. This is called the peer exchange
protocol (PeX). With PeX, peers will be gossipping about known peers and forming
a network, storing peer addresses in the addrbook. Because of this, you don't
have to use a seed node if you have a live persistent peer.

#### Connecting to Peers

To connect to peers on start-up, specify them in the
`$TMHOME/config/config.toml` or on the command line. Use `seeds` to
specify seed nodes, and
`persistent_peers` to specify peers that your node will maintain
persistent connections with.

For example,

```
tendermint node --p2p.seeds "f9baeaa15fedf5e1ef7448dd60f46c01f1a9e9c4@1.2.3.4:26656,0491d373a8e0fcf1023aaf18c51d6a1d0d4f31bd@5.6.7.8:26656"
```

Alternatively, you can use the `/dial_seeds` endpoint of the RPC to
specify seeds for a running node to connect to:

```
curl 'localhost:26657/dial_seeds?seeds=\["f9baeaa15fedf5e1ef7448dd60f46c01f1a9e9c4@1.2.3.4:26656","0491d373a8e0fcf1023aaf18c51d6a1d0d4f31bd@5.6.7.8:26656"\]'
```

Note, with PeX enabled, you
should not need seeds after the first start.

If you want Tendermint to connect to specific set of addresses and
maintain a persistent connection with each, you can use the
`--p2p.persistent_peers` flag or the corresponding setting in the
`config.toml` or the `/dial_peers` RPC endpoint to do it without
stopping Tendermint core instance.

```
tendermint node --p2p.persistent_peers "429fcf25974313b95673f58d77eacdd434402665@10.11.12.13:26656,96663a3dd0d7b9d17d4c8211b191af259621c693@10.11.12.14:26656"

curl 'localhost:26657/dial_peers?persistent=true&peers=\["429fcf25974313b95673f58d77eacdd434402665@10.11.12.13:26656","96663a3dd0d7b9d17d4c8211b191af259621c693@10.11.12.14:26656"\]'
```

### Adding a Non-Validator

Adding a non-validator is simple. Just copy the original `genesis.json`
to `~/.tendermint/config` on the new machine and start the node,
specifying seeds or persistent peers as necessary. If no seeds or
persistent peers are specified, the node won't make any blocks, because
it's not a validator, and it won't hear about any blocks, because it's
not connected to the other peer.

### Adding a Validator

The easiest way to add new validators is to do it in the `genesis.json`,
before starting the network. For instance, we could make a new
`priv_validator.json`, and copy it's `pub_key` into the above genesis.

We can generate a new `priv_validator.json` with the command:

```
tendermint gen_validator
```

Now we can update our genesis file. For instance, if the new
`priv_validator.json` looks like:

```
{
  "address" : "5AF49D2A2D4F5AD4C7C8C4CC2FB020131E9C4902",
  "pub_key" : {
    "value" : "l9X9+fjkeBzDfPGbUM7AMIRE6uJN78zN5+lk5OYotek=",
    "type" : "tendermint/PubKeyEd25519"
  },
  "priv_key" : {
    "value" : "EDJY9W6zlAw+su6ITgTKg2nTZcHAH1NMTW5iwlgmNDuX1f35+OR4HMN88ZtQzsAwhETq4k3vzM3n6WTk5ii16Q==",
    "type" : "tendermint/PrivKeyEd25519"
  },
  "last_step" : 0,
  "last_round" : "0",
  "last_height" : "0"
}
```

then the new `genesis.json` will be:

```
{
  "validators" : [
    {
      "pub_key" : {
        "value" : "h3hk+QE8c6QLTySp8TcfzclJw/BG79ziGB/pIA+DfPE=",
        "type" : "tendermint/PubKeyEd25519"
      },
      "power" : 10,
      "name" : ""
    },
    {
      "pub_key" : {
        "value" : "l9X9+fjkeBzDfPGbUM7AMIRE6uJN78zN5+lk5OYotek=",
        "type" : "tendermint/PubKeyEd25519"
      },
      "power" : 10,
      "name" : ""
    }
  ],
  "app_hash" : "",
  "chain_id" : "test-chain-rDlYSN",
  "genesis_time" : "0001-01-01T00:00:00Z"
}
```

Update the `genesis.json` in `~/.tendermint/config`. Copy the genesis
file and the new `priv_validator.json` to the `~/.tendermint/config` on
a new machine.

Now run `tendermint node` on both machines, and use either
`--p2p.persistent_peers` or the `/dial_peers` to get them to peer up.
They should start making blocks, and will only continue to do so as long
as both of them are online.

To make a Tendermint network that can tolerate one of the validators
failing, you need at least four validator nodes (e.g., 2/3).

Updating validators in a live network is supported but must be
explicitly programmed by the application developer. See the [application
developers guide](./app-development.md) for more details.

### Local Network

To run a network locally, say on a single machine, you must change the
`_laddr` fields in the `config.toml` (or using the flags) so that the
listening addresses of the various sockets don't conflict. Additionally,
you must set `addrbook_strict=false` in the `config.toml`, otherwise
Tendermint's p2p library will deny making connections to peers with the
same IP address.

### Upgrading

The Tendermint development cycle currently includes a lot of breaking changes.
Upgrading from an old version to a new version usually means throwing
away the chain data. Try out the
[tm-migrate](https://github.com/hxzqlh/tm-tools) tool written by
[@hxzqlh](https://github.com/hxzqlh) if you are keen to preserve the
state of your chain when upgrading to newer versions.