** Description changed: Binary package hint: grub2 - Grub2 has switched away from a minimum 1 second delay to hit enter, in - preference to simply holding down shift during the boot sequence. - However, this behaviour doesn't work on all machines. + Ubuntu added a patch on top of mainline GRUB and Debian such that holding down the Shift modifier key during boot will cause it to display + the hidden boot menu. - Further, many users will only learn this after their machine fails to - boot normally, leaving them unable to boot at all without outside - assistance. + In the original IBM PC/AT design the modifier keys (Shifts, Ctrls, Alts) are handled separately to all other keys. Instead of reporting state transitions there is an I/O port register that is read by the software where each bit position represents the current state of the associated + modifier key. + + The functionality to read this I/O port register works correctly for + BIOS systems or UEFI systems starting in Legacy/CSM mode. + + On UEFI systems this does not work. The reasons are: + + 1. At the time this Ubuntu-specific functionality was added to Ubuntu + the UEFI specification, and UEFI implementations by manufacturers, did + not provide a way to detect the state of the modifier keys. + + 2. UEFI only provides the same mechanism as for all other keys: detect a + transition of state (key_down or key_up). + + 3. When GRUB timeout is set to 0 (zero) there is no way to detect a key + press transition. + + It appears that UEFI specification version 2.4 may now support the + required reading of modifier key state so I shall be investigating + whether we can now add support for UEFI systems that implement the v2.4 + specification.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/425979 Title: [UEFI boot only] Holding shift fails to display grub2 menu To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/425979/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
