Manage Logs

Tenable Nessus Agent has the following default log files:

  • nessusd.dump — Nessus Agent dump log file used for debugging output.

    To configure nessusd.dump, see Advanced Settings.

  • nessusd.messages — Nessus Agent message log.

    To configure nessusd.messages, see Advanced Settings.

  • backend.log — Nessus Agent backend log.

    To configure backend.log, see Modify backend.log.

  • nessuscli.log — Nessus Agent CLI log.

Default Log Locations

The following table describes the default log file locations for each operating system.

Operating System Log Location
Windows C:\ProgramData\Tenable\Nessus Agent\nessus\logs
Linux /opt/nessus_agent/var/nessus/logs
macOS /Library/NessusAgent/run/var/nessus/logs

Modify backend.log

You can configure log locations and rotation strategies for backend.log by editing the log.json file. You can also configure custom logs by creating a new reporters[x].reporter section and creating a custom file name.

  1. Using a text editor, open the log.json file, located in the corresponding directory:

    • WindowsC:\ProgramData\Tenable\Nessus Agent\nessus\log.json

    • Linux/opt/nessus_agent/var/nessus/log.json

    • macOS/Library/NessusAgent/run/var/nessus/log.json

  2. For backend.log, edit or create a reporters[x].reporter section, and add or modify the following parameters:

    Parameter Default value Can be modified? Description

    log, info, warn, error, trace


    Determines what log information the log includes.

    • response — Web server activity logs

    • info — Informational logs for a specific task
    • warn — Warning logs for a specific task
    • error — Error logs for a specific task
    • debug — Debugging output
    • verbose — debugging output with more information than debug
    • trace — Logs used to trace output
    type file not recommended Determines the type of the log file.
    rotation_strategy size yes

    Determines whether the log archives files based on maximum rotation size or rotation time.

    Valid values:

    • size — Rotate the log based on size, as specified in max_size.
    • daily — Rotate the log based on time, as specified in rotation_time.
    rotation_time 86400 (1 day) yes

    Rotation time in seconds.

    Only used if rotation_strategy is daily.


    10485760 (10 MB)


    Rotation size in bytes.

    Only used if rotation_strategy is size.




    Maximum number of files allowed in the file rotation.

    The maximum number includes the main file, so 10 max_files is 1 main file and 9 backups. If you decrease this number, Tenable Nessus deletes the old logs.


    Depends on operating system and log file


    The location and name of the log file.

    If you change the name of a default Tenable Nessus Agent log file, some advanced settings may not be able to modify the log settings.

    context true not recommended Enables more context information for logs.


    not recommended

    Determines the format of the output.

    • combined — Presents output in a format used for web server logs.
    • system — Presents output in the default operating system log format.
  3. Save the log.json file.

  4. Restart the Nessus Agent service.

The Nessus Agent updates the log settings.