Configuring Logging

Here we will look at various ways to control log output generated by the node using the json -configuration file of the node.

When you start the node using the default configuration, logging is switched on, log output is directed to the console, minimal severity is Info, and verbosity is normal.

You can change these configurations in the node’s config file, for example: mainnet-config.json`

Enable and disable logs

We can disable logging completely by setting TurnOnLoggin to False:

TurnOnLogging: False

Minimal severity

Log messages come with different severities (Debug, Info, Notice and Warning and Error), and we can specify the minimal severity of messages that will be passed on (the the console, a file or another logging backend). Messages with a lower severity will be suppressed. By changing this minimal severity to Debug, we will therefore see messages of all severities; by changing it to Error, we will only see the most severe messages:

minSeverity: Debug

The severity is displayed in the beginning of each log message (in this example, there is one message with severity Debug, and there are two with severity Notice):


Note: Lowering the minimal severity harms efficiency, so while using a low severity can be very helpful for debugging a problem, it should be used with care during normal operation. The same is true for other options which produce more logging output described below.

Log verbosity

In addition to severity, log messages come with verbosity, which can be MinimalVerbosity, NormalVerbosity or MaximalVerbosity. Changing the verbosity will not change which messages will be displayed, but the amount of information contained in each message.

TracingVerbosity: MinimalVerbosity

By default, log output is directed to the console. This behavior is handled by so-called “scribes”, which we can configure in sections defaultScribes and setupScribes of the configuration file.

Control log output

Section defaultScribes makes types of scribes available. These types are FileSK for writing to a file and StdoutSK for writing to the console. There are also the types JournalSK for systemd’s journal system and DevNullSK for directing the output to nowhere.

Section setupScribes lists those scribes that are actually used. Their kinds must be configured in the defaultScribes section before they can be used. For example, if we want logging to go to logs/mylog.log in Json-format, we can configure this as follows:

  - scKind: FileSK
    scName: "logs/mylog.log"
    scFormat: ScJson

Scribes of type FileSK use rotating log files (keeping the newest log messages in the configured log file and moving older messages to archive files), and the rotation-behavior can be configured in section rotation.


The above configuration options were all global, they effected all subsystems simultaneously. It is possible to activate or deactivate logging for specific subsystems by setting the corresponding flags o True or False accordingly. For example, if we want to activate logging for all subsystems related to block fetching, we can achieve this as follows:

# Trace BlockFetch client.
TraceBlockFetchClient: True

# Trace BlockFetch decisions made by the BlockFetch client.
TraceBlockFetchDecisions: True

# Trace BlockFetch protocol messages.
TraceBlockFetchProtocol: True

# Serialised Trace BlockFetch protocol messages.
TraceBlockFetchProtocolSerialised: True

# Trace BlockFetch server.
TraceBlockFetchServer: True