Manage Logs

Tenable Nessus has the following default log files:

  • nessusd.dump — Nessus dump log file used for debugging output.
  • nessusd.messages — Nessus scanner log.
  • www_server.log — Nessus web server log.
  • backend.log — Nessus backend log.
  • nessuscli.log — Nessuscli log.

Default Log Locations

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

  • Linux — /opt/nessus/var/nessus/logs/<filename>
  • macOS — /Library/Nessus/run/var/nessus/logs/<filename>
  • Windows — C:\ProgramData\Tenable\Nessus\nessus\logs\<filename>

You can customize log file locations when you modify log settings.

Modify Log Settings

To modify log settings, use one of the following methods, depending on the log file:

Modify log.json

You can configure log locations and rotation strategies for www_server.log and 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.

Note: You cannot configure nessusd.dump or nessusd.messages settings using log.json. Configure those log settings using logfile_rot in the advanced settings.

To modify log settings using log.json:

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

    • Linux — /opt/nessus/var/nessus/log.json
    • macOS/Library/Nessus/run/var/nessus/log.json
    • WindowsC:\ProgramData\Tenable\Nessus\nessus\log.json
  2. For each log file, edit or create a reporters[x].reporter section, and add or modify the parameters described in log.json Format.

  3. Save the log.json file.
  4. Restart the Tenable Nessus service.

    The Tenable Nessus updates the log settings.

log.json Format

The following describe parameters in the log.json file, and whether Tenable recommends that you modify the parameter. Some parameters are advanced and you do not need to modify them often. If you are an advanced user who wants to configure a custom log file with advanced parameters, see the knowledge base article for more information.

Parameter Default value Can be modified? Description

www_server.log: response

backend.log: log, info, warn, error, trace

www_server.log: no

backend.log: yes

Determines what log information the log includes.

  • response — Web server activity logs

    Note: response is the only valid tag for www_server.log.

  • 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.


Tenable Nessus: 536870912 (512 MB)

Agent: 10485760 (10 MB)


Rotation size in bytes.

Only used if rotation_strategy is size.


Tenable Nessus10

Agent: 2


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. See Default Log Locations.

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

context true not recommended Enables more context information for logs in the system format, such as backend.log.
format www_server.log: combined

backend.log: system

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.

The following are examples of a log.json file.