FortiSwitch: secure, simple and scalable Ethernet solutions
In some rare scenarios, if FortiSwitch upgrade fails via GUI and CLI, upgrade the via boot sequence is possible.

This article describes how to upgrade a FortiSwitch via the boot sequence.

1) Plug in the console cable to the Fortiswitch and access it using baud rate of 115200.
2) Download the latest/required image for the Fortiswitch in local PC, the image name will be like :FSW_124E_POE-v6-build0176-FORTINET.out.
3) Setup a TFTP server in the local PC with server/PC IP as Connect this PC to Ethernet port of the FortiSwitch.
4) Interrupt the boot sequence of the Fortiswitch and configure the required TFTP parameters.
Upgrade via boot sequence:

AIFL-ACCESS-SW2 # execute reboot                                     This operation will reboot the system !                               Do you want to continue? (y/n)y
System is rebooting...
FortiSwitch-124E-POE (11:27-11.14.2017)                               BIOS version : 04000006                                         Serial number: S124EP5918007585
Please wait for OS to boot, or press any key to display configuration menu...  1
[G]:  Get firmware image from TFTP server.
[F]:  Format boot device.
[I]:  Configuration and Information.
[U]:  Upgrade BIOS image.
[R]:  Reboot FortiSwitch.
[Q]:  Quit menu and continue to boot.
[H]:  Display this list of options.
Enter G,F,I,U,R,Q,or H: G
Enter network port [port1]:                             
Enter TFTP server address []:
Enter local address []:
Enter local netmask []:
Enter default gateway []:
Enter firmware image file name [image.out]: FSW_124E_POE-v6-build0176-FORTINET.out
Save as Default/Run without saving:[D/R]? D

Loading [ 19529261, 19529261 ]   Success
Saving to default partition ... 100%
Booting default partition : FortiSwitch-124E-POE v6.2.1,build0176,190620
Booting FortiSwitch.
System is started.

SW# get  system  status
Version: FortiSwitch-124E-POE v6.2.1,build0176,190620 (GA)