--- order: 7 --- ## Logging Logging adds detail and allows the node operator to better identify what they are looking for. Tendermint supports log levels on a global and per-module basis. This allows the node operator to see only the information they need and the developer to hone in on specific changes they are working on. ## Configuring Log Levels There are three log levels, `info`, `debug` and `error`. These can be configured either through the command line via `tendermint start --log-level ""` or within the `config.toml` file. - `info` Info represents an informational message. It is used to show that modules have started, stopped and how they are functioning. - `debug` Debug is used to trace various calls or problems. Debug is used widely throughout a codebase and can lead to overly verbose logging. - `error` Error represents something that has gone wrong. An error log can represent a potential problem that can lead to a node halt. Within the `config.toml`: ```toml # Output level for logging, including package level options log-level = "info" ``` Via the command line: ```sh tendermint start --log-level "info" ``` ## List of modules Here is the list of modules you may encounter in Tendermint's log and a little overview what they do. - `abci-client` As mentioned in [Application Architecture Guide](../app-dev/app-architecture.md), Tendermint acts as an ABCI client with respect to the application and maintains 3 connections: mempool, consensus and query. The code used by Tendermint Core can be found [here](https://github.com/tendermint/tendermint/blob/v0.35.x/abci/client). - `blockchain` Provides storage, pool (a group of peers), and reactor for both storing and exchanging blocks between peers. - `consensus` The heart of Tendermint core, which is the implementation of the consensus algorithm. Includes two "submodules": `wal` (write-ahead logging) for ensuring data integrity and `replay` to replay blocks and messages on recovery from a crash. [here](https://github.com/tendermint/tendermint/blob/v0.35.x/types/events.go). You can subscribe to them by calling `subscribe` RPC method. Refer to [RPC docs](../tendermint-core/rpc.md) for additional information. - `mempool` Mempool module handles all incoming transactions, whenever they are coming from peers or the application. - `p2p` Provides an abstraction around peer-to-peer communication. For more details, please check out the [README](https://github.com/tendermint/spec/tree/master/spec/p2p). - `rpc-server` RPC server. For implementation details, please read the [doc.go](https://github.com/tendermint/tendermint/blob/v0.35.x/rpc/jsonrpc/doc.go). - `state` Represents the latest state and execution submodule, which executes blocks against the application. - `statesync` Provides a way to quickly sync a node with pruned history. ### Walkabout example We first create three connections (mempool, consensus and query) to the application (running `kvstore` locally in this case). ```sh I[10-04|13:54:27.364] Starting multiAppConn module=proxy impl=multiAppConn I[10-04|13:54:27.366] Starting localClient module=abci-client connection=query impl=localClient I[10-04|13:54:27.366] Starting localClient module=abci-client connection=mempool impl=localClient I[10-04|13:54:27.367] Starting localClient module=abci-client connection=consensus impl=localClient ``` Then Tendermint Core and the application perform a handshake. ```sh I[10-04|13:54:27.367] ABCI Handshake module=consensus appHeight=90 appHash=E0FBAFBF6FCED8B9786DDFEB1A0D4FA2501BADAD I[10-04|13:54:27.368] ABCI Replay Blocks module=consensus appHeight=90 storeHeight=90 stateHeight=90 I[10-04|13:54:27.368] Completed ABCI Handshake - Tendermint and App are synced module=consensus appHeight=90 appHash=E0FBAFBF6FCED8B9786DDFEB1A0D4FA2501BADAD ``` After that, we start a few more things like the event switch, reactors, and perform UPNP discover in order to detect the IP address. ```sh I[10-04|13:54:27.374] Starting EventSwitch module=types impl=EventSwitch I[10-04|13:54:27.375] This node is a validator module=consensus I[10-04|13:54:27.379] Starting Node module=main impl=Node I[10-04|13:54:27.381] Local listener module=p2p ip=:: port=26656 I[10-04|13:54:27.382] Getting UPNP external address module=p2p I[10-04|13:54:30.386] Could not perform UPNP discover module=p2p err="write udp4 0.0.0.0:38238->239.255.255.250:1900: i/o timeout" I[10-04|13:54:30.386] Starting DefaultListener module=p2p impl=Listener(@10.0.2.15:26656) I[10-04|13:54:30.387] Starting P2P Switch module=p2p impl="P2P Switch" I[10-04|13:54:30.387] Starting MempoolReactor module=mempool impl=MempoolReactor I[10-04|13:54:30.387] Starting BlockchainReactor module=blockchain impl=BlockchainReactor I[10-04|13:54:30.387] Starting ConsensusReactor module=consensus impl=ConsensusReactor I[10-04|13:54:30.387] ConsensusReactor module=consensus fastSync=false I[10-04|13:54:30.387] Starting ConsensusState module=consensus impl=ConsensusState I[10-04|13:54:30.387] Starting WAL module=consensus wal=/home/vagrant/.tendermint/data/cs.wal/wal impl=WAL I[10-04|13:54:30.388] Starting TimeoutTicker module=consensus impl=TimeoutTicker ``` Notice the second row where Tendermint Core reports that "This node is a validator". It also could be just an observer (regular node). Next we replay all the messages from the WAL. ```sh I[10-04|13:54:30.390] Catchup by replaying consensus messages module=consensus height=91 I[10-04|13:54:30.390] Replay: New Step module=consensus height=91 round=0 step=RoundStepNewHeight I[10-04|13:54:30.390] Replay: Done module=consensus ``` "Started node" message signals that everything is ready for work. ```sh I[10-04|13:54:30.391] Starting RPC HTTP server on tcp socket 0.0.0.0:26657 module=rpc-server I[10-04|13:54:30.392] Started node module=main nodeInfo="NodeInfo{id: DF22D7C92C91082324A1312F092AA1DA197FA598DBBFB6526E, moniker: anonymous, network: test-chain-3MNw2N [remote , listen 10.0.2.15:26656], version: 0.11.0-10f361fc ([wire_version=0.6.2 p2p_version=0.5.0 consensus_version=v1/0.2.2 rpc_version=0.7.0/3 tx_index=on rpc_addr=tcp://0.0.0.0:26657])}" ``` Next follows a standard block creation cycle, where we enter a new round, propose a block, receive more than 2/3 of prevotes, then precommits and finally have a chance to commit a block. For details, please refer to [Byzantine Consensus Algorithm](https://github.com/tendermint/spec/blob/master/spec/consensus/consensus.md). ```sh I[10-04|13:54:30.393] enterNewRound(91/0). Current: 91/0/RoundStepNewHeight module=consensus I[10-04|13:54:30.393] enterPropose(91/0). Current: 91/0/RoundStepNewRound module=consensus I[10-04|13:54:30.393] enterPropose: Our turn to propose module=consensus proposer=125B0E3C5512F5C2B0E1109E31885C4511570C42 privValidator="PrivValidator{125B0E3C5512F5C2B0E1109E31885C4511570C42 LH:90, LR:0, LS:3}" I[10-04|13:54:30.394] Signed proposal module=consensus height=91 round=0 proposal="Proposal{91/0 1:21B79872514F (-1,:0:000000000000) {/10EDEDD7C84E.../}}" I[10-04|13:54:30.397] Received complete proposal block module=consensus height=91 hash=F671D562C7B9242900A286E1882EE64E5556FE9E I[10-04|13:54:30.397] enterPrevote(91/0). Current: 91/0/RoundStepPropose module=consensus I[10-04|13:54:30.397] enterPrevote: ProposalBlock is valid module=consensus height=91 round=0 I[10-04|13:54:30.398] Signed and pushed vote module=consensus height=91 round=0 vote="Vote{0:125B0E3C5512 91/00/1(Prevote) F671D562C7B9 {/89047FFC21D8.../}}" err=null I[10-04|13:54:30.401] Added to prevote module=consensus vote="Vote{0:125B0E3C5512 91/00/1(Prevote) F671D562C7B9 {/89047FFC21D8.../}}" prevotes="VoteSet{H:91 R:0 T:1 +2/3:F671D562C7B9242900A286E1882EE64E5556FE9E:1:21B79872514F BA{1:X} map[]}" I[10-04|13:54:30.401] enterPrecommit(91/0). Current: 91/0/RoundStepPrevote module=consensus I[10-04|13:54:30.401] enterPrecommit: +2/3 prevoted proposal block. Locking module=consensus hash=F671D562C7B9242900A286E1882EE64E5556FE9E I[10-04|13:54:30.402] Signed and pushed vote module=consensus height=91 round=0 vote="Vote{0:125B0E3C5512 91/00/2(Precommit) F671D562C7B9 {/80533478E41A.../}}" err=null I[10-04|13:54:30.404] Added to precommit module=consensus vote="Vote{0:125B0E3C5512 91/00/2(Precommit) F671D562C7B9 {/80533478E41A.../}}" precommits="VoteSet{H:91 R:0 T:2 +2/3:F671D562C7B9242900A286E1882EE64E5556FE9E:1:21B79872514F BA{1:X} map[]}" I[10-04|13:54:30.404] enterCommit(91/0). Current: 91/0/RoundStepPrecommit module=consensus I[10-04|13:54:30.405] Finalizing commit of block with 0 txs module=consensus height=91 hash=F671D562C7B9242900A286E1882EE64E5556FE9E root=E0FBAFBF6FCED8B9786DDFEB1A0D4FA2501BADAD I[10-04|13:54:30.405] Block{ Header{ ChainID: test-chain-3MNw2N Height: 91 Time: 2017-10-04 13:54:30.393 +0000 UTC NumTxs: 0 LastBlockID: F15AB8BEF9A6AAB07E457A6E16BC410546AA4DC6:1:D505DA273544 LastCommit: 56FEF2EFDB8B37E9C6E6D635749DF3169D5F005D Data: Validators: CE25FBFF2E10C0D51AA1A07C064A96931BC8B297 App: E0FBAFBF6FCED8B9786DDFEB1A0D4FA2501BADAD }#F671D562C7B9242900A286E1882EE64E5556FE9E Data{ }# Commit{ BlockID: F15AB8BEF9A6AAB07E457A6E16BC410546AA4DC6:1:D505DA273544 Precommits: Vote{0:125B0E3C5512 90/00/2(Precommit) F15AB8BEF9A6 {/FE98E2B956F0.../}} }#56FEF2EFDB8B37E9C6E6D635749DF3169D5F005D }#F671D562C7B9242900A286E1882EE64E5556FE9E module=consensus I[10-04|13:54:30.408] Executed block module=state height=91 validTxs=0 invalidTxs=0 I[10-04|13:54:30.410] Committed state module=state height=91 txs=0 hash=E0FBAFBF6FCED8B9786DDFEB1A0D4FA2501BADAD I[10-04|13:54:30.410] Recheck txs module=mempool numtxs=0 height=91 ```