Recently we experienced an issue with a FortiGate firewall where you could not access the GUI using the management IP address although it had been working without issues previously. SSH/Ping/Etc. were still functional but the GUI did not respond when trying to open the management page to log in. Additionally the configuration had not changed nor had the device experienced any issues that required reloading the configuration. After some research, the fix (if rebooting is not an option) is to access the device using SSH, login as admin, then execute the following commands:
# config global
# get sys perf top – This will display all the running processes in the FortiGate (the second column is the process ID’s) note the ones you want to restart. In our case it was the two “httpsd” processes.
# diag sys kill 11 <process-id> – Using the process ID from above you can restart a process using this command.
After running these commands, the GUI was then accessible again. Nice to know how to view the running processes for instances like this or resolving other issues.