Can't boot notebook from SSD

[Petter Adsen]

On 03/05/17 14:49, Liam Proven wrote:
> On 3 May 2017 at 14:44, Ken D'Ambrosio <ken at jots.org> wrote:
>> Looks like you're right, Liam.  I honestly thought it was okay to have a
>> small EFI partition, so long as you (generically) weren't getting it mixed
>> up with a /boot partition.  But Teh Docs say otherwise:
>> https://help.ubuntu.com/community/DiskSpace
>>
>> That being said, it's my impression that if you're loading your kernel (as
>> the OP seems to be), you're already past the EFI part of the boot process.
> 
> 
> Some of what were NVRAM settings in BIOSes are held in files in that
> partition in EFI systems.

Actually, they're mounted in /sys/firmware/efi/efivars (checking if this
exists is also a quick way to determine whether you are booted in UEFI
mode). In other words, they are NVRAM settings accessible as files.

> This means that if they are wiped, you can brick your system.
> 
> http://www.phoronix.com/scan.php?page=news_item&px=UEFI-rm-root-directory

This was a bug found on a few early UEFI-based machines from either
Samsung or Toshiba IIRC, where the machine can be bricked by doing
things it didn't expect with the firmware variables. On a proper UEFI
firmware implementation deleting the variables should be a recoverable
problem, you would just need to set up the firmware pointers to the
bootloader(s) etc again.

https://bugs.launchpad.net/ubuntu-cdimage/+bug/1040557
https://askubuntu.com/a/298716
https://askubuntu.com/questions/521293/an-ubuntu-command-bricked-my-system#767286red

> Ergo, there must be enough space to _write_ to those files, or it won't boot.

AFAIK the firmware does not need to write to the EFI system partition at
any point, but more than 1MB of space is certainly recommended. It
depends on how many bootloaders you wish to store there and how much
space they consume.

On a system like Arch, for example, the kernel and initramfs is also
stored on the EFI partition, so you will need at least 50-100MB for that
alone.

OTOH, grub doesn't take a lot of space, so if you don't intend to
install a second OS you might get away with 1MB.

Petter