# 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 [127.0.0.1:46658](127.0.0.1:46658). 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 in the [ABCI repository](https://github.com/tendermint/abci). 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:46657/broadcast_tx_commit?tx=\"abcd\" We can see the chain's status at the `/status` end-point: curl http://localhost:46657/status | json_pp and the `latest_app_hash` in particular: curl http://localhost:46657/status | json_pp | grep latest_app_hash Visit http://localhost:46657> 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:46657/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:46657/broadcast_tx_commit?tx=\"hello\" Using a special character: curl 'http://localhost:46657/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:46657/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:46657 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.html). 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" : "AC26791624DE60" }, "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" : "AC26791624DE60" }, "last_height" : 0, "priv_key" : { "value" : "JPivl82x+LfVkp8i3ztoTjY6c6GJ4pBxQexErOCyhwqHeGT5ATxzpAtPJKnxNx/NyUnD8Ebv3OIYH+kgD4N88Q==", "type" : "954568A3288910" } } 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.html#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@1.2.3.4:46656,0491d373a8e0fcf1023aaf18c51d6a1d0d4f31bd@5.6.7.8:46656" Alternatively, you can use the `/dial_seeds` endpoint of the RPC to specify seeds for a running node to connect to: curl 'localhost:46657/dial_seeds?seeds=\["f9baeaa15fedf5e1ef7448dd60f46c01f1a9e9c4@1.2.3.4:46656","0491d373a8e0fcf1023aaf18c51d6a1d0d4f31bd@5.6.7.8:46656"\]' 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@10.11.12.13:46656,96663a3dd0d7b9d17d4c8211b191af259621c693@10.11.12.14:46656" curl 'localhost:46657/dial_peers?persistent=true&peers=\["429fcf25974313b95673f58d77eacdd434402665@10.11.12.13:46656","96663a3dd0d7b9d17d4c8211b191af259621c693@10.11.12.14:46656"\]' ### 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" : "AC26791624DE60" }, "priv_key" : { "value" : "EDJY9W6zlAw+su6ITgTKg2nTZcHAH1NMTW5iwlgmNDuX1f35+OR4HMN88ZtQzsAwhETq4k3vzM3n6WTk5ii16Q==", "type" : "954568A3288910" }, "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" : "AC26791624DE60" }, "power" : 10, "name" : "" }, { "pub_key" : { "value" : "l9X9+fjkeBzDfPGbUM7AMIRE6uJN78zN5+lk5OYotek=", "type" : "AC26791624DE60" }, "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.html) 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.