# 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
# Directory Root
The default directory for blockchain data is
this by setting the
TMHOME environment variable.
Initialize the root directory by running:
This will create a new private key (
priv_validator_key.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:
genesis.json file in
$TMHOME/config/ defines the initial
TendermintCore state upon genesis of the blockchain (see
genesis_time: Official time of blockchain start.
chain_id: ID of the blockchain. This must be unique for every blockchain. If your testnet blockchains do not have unique chain IDs, you will have a bad time. The ChainID must be less than 50 symbols.
time_iota_ms: Minimum time increment between consecutive blocks (in milliseconds). If the block header timestamp is ahead of the system clock, decrease this value.
validators: List of initial validators. Note this may be overridden entirely by the application, and may be left empty to make explicit that the application will initialize the validator set with ResponseInitChain.
pub_key: The first element specifies the
pub_keytype. 1 == Ed25519. The second element are the pubkey bytes.
power: The validator's voting power.
name: Name of the validator (optional).
app_hash: The expected application hash (as returned by the
ResponseInfoABCI message) upon genesis. If the app's hash does not match, Tendermint will panic.
app_state: The application state (e.g. initial distribution of tokens).
# Sample genesis.json
To run a Tendermint node, use:
By default, Tendermint will try to connect to an ABCI application on
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
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
apps that ship as examples with
abci-cli. It's easy to compile your app
in-process with Tendermint if it's written in Go. If your app is not written in
Go, run it in another process, and use the
--proxy_app flag to specify the
address of the socket it is listening on, for instance:
You can find out what flags are supported by running
tendermint node --help.
To send a transaction, use
curl to make requests to the Tendermint RPC
server, for example:
We can see the chain's status at the
latest_app_hash in particular:
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.
Find the RPC Documentation here
The following nuances when sending/formatting transactions should be taken into account:
To send a UTF8 string byte array, quote the value of the tx pramater:
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:
Using a special character:
sends a 4 byte transaction: "€5" (UTF8) [e2 82 ac 35].
To send as raw hex, omit quotes AND prefix the hex string with
which sends a 4 byte transaction: [01 02 03 04].
json), the raw hex must be
which sends the same 4 byte transaction: [01 02 03 04].
Note that raw hex cannot be used in
UNSAFE Only do this in development and only if you can afford to lose all blockchain data!
To reset a blockchain, stop the node and run:
This command will remove the data directory and reset private validator and address book files.
Tendermint uses a
config.toml for configuration. For details, see the
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
Some fields from the config file can be overwritten with flags.
# No Empty Blocks
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:
or set the configuration via the
Remember: because the default is to create empty blocks, avoiding
empty blocks requires the config option to be set to
The block interval setting allows for a delay (in time.Duration format ParseDuration) between the creation of each new empty block. It can be set with this additional flag:
or set the configuration via the
With this setting, empty blocks will be produced every 5s if no block
has been produced otherwise, regardless of the value of
# 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
CheckTx against the application. If it passes
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:
These correspond to no-processing, processing through the mempool, and
processing through a block, respectively. That is,
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
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
CheckTx. The return value for
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.
Note the mempool does not provide strong guarantees - just because a tx passed CheckTx (ie. was accepted into the mempool), doesn't mean it will be committed, as nodes with the tx in their mempool may crash before they get to propose. For more information, see the mempool write-ahead-log
# Tendermint Networks
tendermint init is run, both a
priv_validator_key.json are created in
genesis.json might look like:
priv_validator_key.json actually contains a private key, and should
thus be kept absolutely secret; for now we work with the plain text.
last_ fields, which are used to prevent us from signing
Note also that the
pub_key (the public key) in the
priv_validator_key.json is also present in the
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_key.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).
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.
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
specify seed nodes, and
persistent_peers to specify peers that your node will maintain
persistent connections with.
Alternatively, you can use the
/dial_seeds endpoint of the RPC to
specify seeds for a running node to connect to:
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.
# Adding a Non-Validator
Adding a non-validator is simple. Just copy the original
~/.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
before starting the network. For instance, we could make a new
priv_validator_key.json, and copy it's
pub_key into the above genesis.
We can generate a new
priv_validator_key.json with the command:
Now we can update our genesis file. For instance, if the new
priv_validator_key.json looks like:
then the new
genesis.json will be:
~/.tendermint/config. Copy the genesis
file and the new
priv_validator_key.json to the
a new machine.
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 for more details.
# Local Network
To run a network locally, say on a single machine, you must change the
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
addr_book_strict=false in the
config.toml, otherwise Tendermint's p2p
library will deny making connections to peers with the same IP address.
See the UPGRADING.md guide. You may need to reset your chain between major breaking releases. Although, we expect Tendermint to have fewer breaking releases in the future (especially after 1.0 release).