Legacy BIOS Toshiba won't boot Linux from SSD despite successful grub-install — tried Mint, antiX, Zorin, now MX Linux
This isn't my first attempt — I've previously tried Linux Mint, antiX, and now Zorin OS, all with similar boot problems on this specific laptop (GRUB/MBR issues tied to the legacy BIOS). I'm now testing MX Linux as well.
Most recently, I installed Zorin OS 18.1 (Ubuntu-based) from a live USB. Installation completed with no errors, and the live USB always boots fine. But the system won't boot on its own from the internal SSD — without the USB stick, the laptop either shows a blank screen, falls through to PXE/network boot (Intel UNDI, PXE-2.1), or lands on the Toshiba's manual Boot Menu instead of loading GRUB.
Diagnosis so far
Confirmed via ls /sys/firmware/efi in the live session that the system boots in BIOS/legacy mode, not UEFI.
Checked the partition table in the installer: the disk has
sda1 — bios_grub, 1MB
sda2 — EFI, FAT32, ~537MB
sda3 — ext4, root, Zorin OS 18.1
So it's a GPT disk with both a bios_grub partition and an EFI partition — a hybrid layout.
Repair attempt (chroot from live USB)
Código
grub-install reported "Installation finished. No error reported." update-grub found the kernel/initrd correctly. Exited chroot, unmounted everything, rebooted.
Result: no change. Still fails to boot from the SSD, still falls back to the Boot Menu / PXE, despite grub-install reporting success and the bios_grub partition existing on the GPT disk.
Question
Given grub-install --target=i386-pc completed without error, why would legacy BIOS still fail to find a bootable GRUB image on this GPT disk? Anyone run into the bios_grub flag not getting set correctly by the Ubuntu/Zorin installer, or some other gotcha with GPT + legacy BIOS on old hardware like this? Is this a recurring incompatibility with this specific Toshiba/Phoenix BIOS combo, given I've had similar issues across multiple distros?
Current plan
Since the GPT + EFI + bios_grub hybrid setup seems fragile for legacy BIOS booting, I'm doing a clean install of MX Linux 25.1 (Xfce, sysvinit) using an MBR partition table from the start to sidestep the GPT issues entirely.