Parametrize the log level

This section explains how to parametrize the log output level of hermes.

The configuration file permits parametrization of output verbosity via the knob called log_level. This file is loaded by default from $HOME/.hermes/config.toml, but can be overridden in all commands with the --config flag, e.g. hermes --config $CONFIGPATH subcommand.

Relevant snippet:

log_level = 'error'

Valid options for log_level are: 'error', 'warn', 'info', 'debug', 'trace'. These levels correspond to the tracing subcomponent of the relayer-cli, see here.

Hermes will always print a last line summarizing the result of its operation for queries or transactions. In addition to this last line, arbitrary debug, info, or other outputs may be produced.

Overriding the tracing filter using RUST_LOG

For debugging purposes, we may want to inspect which RPC queries Hermes is making. Hermes makes use of the tendermint-rpc library to issue RPC queries, but the output of this library is by default turned off in order to keep the logs more readable.

Using the RUST_LOG environment variable, we can turn logging on for the tendermint-rpc library, as follows:

RUST_LOG=tendermint-rpc=debug,info hermes start

Setting the RUST_LOG environment variable to tendermint_rpc=debug,info instructs Hermes to set the log level of the tendermint_rpc crate to debug and otherwise use the info log level.

Note: While the tendermint-rpc contains a dash in its name, the logging filter expects a module name, which can only contain alphanumeric characters and underscores, hence why the filter above is written tendermint_rpc=debug.


❯ RUST_LOG=tendermint_rpc=debug,info hermes start
2022-02-24T14:32:14.039555Z  INFO ThreadId(01) using default configuration from '/Users/coromac/.hermes/config.toml'
2022-02-24T14:32:14.043500Z  INFO ThreadId(01) telemetry service running, exposing metrics at
2022-02-24T14:32:14.043542Z  INFO ThreadId(01) [rest] address not configured, REST server disabled
2022-02-24T14:32:14.049759Z DEBUG ThreadId(01) Incoming response: {
  "jsonrpc": "2.0",
  "id": "143b4580-c49e-47c1-81b2-4e7090f6e762",
  "result": {
    "node_info": {
      "protocol_version": {
        "p2p": "8",
        "block": "11",
        "app": "0"
      "id": "73f9134539f9845cd253dc302e36d48ee4c0f32d",
      "listen_addr": "tcp://",
      "network": "ibc0",
      "version": "v0.34.14",
      "channels": "40202122233038606100",
      "moniker": "ibc0",
      "other": {
        "tx_index": "on",
        "rpc_address": "tcp://"
    "sync_info": {
      "latest_block_hash": "8396B93E355AD80EED8167A04BB9858A315A8BEB482547DE16A6CD82BC11551B",
      "latest_app_hash": "22419E041D6997EE75FF66F7F537A3D36122B220EAB89A9C246FEF680FB1C97A",
      "latest_block_height": "86392",
      "latest_block_time": "2022-02-24T14:32:08.673989Z",
      "earliest_block_hash": "0A73CFE8566D4D4FBFE3178D9BCBAD483FD689854CA8012FF1457F8EC4598132",
      "earliest_app_hash": "E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855",
      "earliest_block_height": "1",
      "earliest_block_time": "2022-01-20T09:04:21.549736Z",
      "catching_up": false
    "validator_info": {
      "address": "6FD56E6AA1EEDAD227AFAB6B9DE631719D4A3691",
      "pub_key": {
        "type": "tendermint/PubKeyEd25519",
        "value": "mR5V/QWOv/mJYyNmlsl3mfxKy1PNaOzdztyas4NF2BA="
      "voting_power": "10"
2022-02-24T14:32:14.052503Z DEBUG ThreadId(21) Incoming response: {
  "jsonrpc": "2.0",
  "id": "0ca35e64-ea98-4fbf-bd66-c3291128ace9",
  "result": {}


The two DEBUG log lines above were emitted by the tendermint-rpc crate.