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nsoni
Staff
Staff
May 19, 2025

Troubleshooting Tip: 'Backend error code: 255' error during new parser XML validation

  • May 19, 2025
  • 0 replies
  • 941 views
Description The article provides steps to troubleshoot the 'Backend error code: 255' error during new parser XML validation.
Scope FortiSIEM with EventDB (/data) as event storage.
Solution

When creating a new parser in FortiSIEM, the 'Backend error code: 255' error appears upon selecting the Validate button:

 

backend_error_255.png

 

Cause: The directory /data/custParser does not exist or lacks appropriate permissions. FortiSIEM requires this directory to store and validate custom parsers.

 

Solution:

Step 1: Create the Missing Directory.

Log in as a privileged user and execute the following commands to create the directory and set ownership:

 

mkdir /data/custParser

chown admin:admin /data/custParser

 

If permissions need to be recursively set:

 

chown -R admin:admin /data/custParser

 

Step 2: Validate File Permissions.

Check that the admin user can read/write within the /data directory:

 

su admin

ls -ltrh /data/

touch /data/testfile.txt

 

If these commands fail, verify and correct NFS export permissions if /data is NFS-mounted. Ensure the following options are set on the NFS server:

  • rw.
  • sync.
  • no_root_squash.

Refer to the NFS server setup guide for a Linux OS based NFS server:
Installing NFS Server for FortiSIEM Event Storage

 

Additionally, make sure to create and save the custom parser before testing it; otherwise, a 255 backend error will occur. After saving, select Validate and then proceed with the Test option.