AstLinux 1.4.5 or earlier only supports Legacy BIOS (non-UEFI) booting.
The AstLinux disk has a FAT16 formatted 1st partition marked as bootable with a master boot record (MBR). Legacy BIOS hardware will jump to syslinux installed on the FAT16 partition which in turn calls RUNNIX (minimal Linux kernel also on the FAT16 partition), and lastly kexec the desired AstLinux run image.
New installations of AstLinux 1.4.6 or later support both Legacy BIOS booting and UEFI booting. These new installations include RUNNIX 0.6.10 or later.
RUNNIX 0.6.10 or later is required to boot using UEFI.
For the UEFI case, the FAT16 formatted 1st partition contains the file path EFI/BOOT/bootx64.efi generated by syslinux. This EFI/BOOT/bootx64.efi is the “fallback” boot loader path-name that UEFI firmware on 64-bit x86 systems support.
Old Installation Upgrade to UEFI boot:
If you have upgraded an old system to AstLinux 1.4.6 or later, you will continue to use Legacy BIOS as you did before. By default, if you have a RUNNIX version earlier than 0.6.10 and you upgrade to RUNNIX 0.6.10 or later, you will continue to use Legacy BIOS as you did before. This is typically what you want.
Upgrading RUNNIX will not add UEFI files in the EFI/BOOT/ directory if that path does not exist, which is the case for old installations.
If for some reason you want to enable UEFI boot in your hardware's BIOS for an old installation, you can manually perform the following steps …
First upgrade to AstLinux 1.4.6 or later and reboot.
Then, from the CLI:
mount -o rw,remount /oldroot/cdrom mkdir -p /oldroot/cdrom/EFI/BOOT mount -o ro,remount /oldroot/cdrom upgrade-RUNNIX-image upgrade
Then reboot and enter your hardware's BIOS Setup and enable UEFI or UEFI only. Save and boot, you should now boot using UEFI.