Troubleshooting Tip: 'System files integrity check failed!' message observed when performing downgrade from FortiOS 7.2.5+ to FortiOS 6.4

[desaia]

Description	The article describes troubleshooting steps to take if the FortiGate enters a boot loop when performing a downgrade from FortiOS 7.2.5+ to FortiOS 6.4.
Scope	FortiOS 7.2.5 and above, 6.4 and above.
Solution	When performing a downgrade from FortiOS 7.2.5+ to the 6.4 version, the console logs show a 'System files integrity check failed!' message during the bootup process. To perform a downgrade from FortiOS 7.2.5 + to FortiOS 6.4 - use a different security level (the default is security level 2) in the BIOS options. Power down the FortiGate and interrupt the booting sequence once it is booting up. Follow the steps below: Press any key to display configuration menu... <- Press any key to interrupt the booting sequence here. ............................. [C]: Configure TFTP parameters. [R]: Review TFTP parameters. [T]: Initiate TFTP firmware transfer. [F]: Format boot device. [I]: System information. [B]: Boot with backup firmware and set as default. [Q]: Quit menu and continue to boot. [H]: Display this list of options. Enter C,R,T,F,I,B,Q,or H: <- (Press I (for System Information)) [S]: Set serial port baudrate. [R]: Set restricted mode. [T]: Set menu timeout. [U]: Set security level. <- press U (for Set security level). [I]: Display system information. [E]: Reset system configuration [Q]: Quit this menu. [H]: Display this list of options. In the security level menu, choose 'Use security level 1 or 0'. Perform the reboot again - the FortiGate will reboot with the FortiOS 6.4 version.