Troubleshooting Tip: FortiADC GUI login page becomes unresponsive after selecting login

The FortiADC graphical login page may appear normal, and credentials can be entered. After selecting Login, the page may stall without displaying an error message. Browser developer tools may show that the login request is rejected by the server engine endpoint. Example observation in the browser network inspector:

HTTP 401 response from endpoint: touch?vdom

This indicates that the request reached the application layer, but the login process could not be completed. Secure Shell access to the device is typically still available. When connecting through the command line interface, the following error may sometimes appear:

error: wc: standard output: Cannot allocate memory

This condition is often associated with the temporary directory approaching full capacity. When the /tmp directory becomes heavily utilized, the FortiADC graphical user interface service may fail to allocate temporary files required for authentication processing. This behavior may also coincide with high-availability environments where devices fall out of synchronization.

1. Verify high availability status.

Run the following command to confirm synchronization status: get system ha-status.

If the cluster reports a synchronization issue, perform a manual configuration synchronization:

execute ha force sync-config all

2. Restore graphical login access.

In many observed cases, clearing temporary files through a system reboot restores the graphical login functionality.

execute reboot

3. Consider high availability behavior before rebooting.

When FortiADC operates in Active-Passive high availability mode, a reboot can often be performed without traffic interruption if the peer device is healthy and synchronized. If synchronization status reports 'Not Sync', perform synchronization before rebooting.

4. Advanced troubleshooting (Fortinet Technical Assistance Center).

If the issue occurs repeatedly, a deeper investigation may be required to inspect temporary file usage and graphical service behavior. Fortinet Support may collect diagnostic information using backend shell commands similar to the following:

# find /tmp -maxdepth 1 -type f -print0 2>/dev/null | xargs -0 du -h 2>/dev/null # cat /var/log/nginx/error_log # ls -LS /tmp # df -h

These commands help identify large temporary files and verify whether storage exhaustion is preventing graphical login sessions from being created. If the issue persists after a reboot, further investigation by Fortinet Support may be required.