On Sat, Sep 8, 2018 at 4:02 PM Tom Horsley <horsley1...@gmail.com> wrote:


> I've been trying to decrypt efibootmgr docs and I've given up :-).
>
> I keep getting the impression you can't examine any efi boot info
> other than the one currently active which you booted from.

"efibootmgr" displays the boot entries held in nvram, whether those
entries refer to files that exist in the current boot or not. (The
files must exist in order to be added.)


> What if I want to stick a removable disk into the system and examine
> the boot parameters on it? Any way to point efi tools to a completely
> separate non-root disk that just happens to be plugged into the system?

There are no boot parameters on the stick. But there may be an nvram
boot entry pointing to an efi executable on the stick. But you don't
need the stick to be plugged-in for that entry to be displayed by
"efibootmgr".

You can add a boot entry pointing to a file on the stick. I don't have
a stick at hand, but to add the default "bootx64.efi" on my laptop:


%% display boot entries %%
# efibootmgr
BootCurrent: 0000
Timeout: 0 seconds
BootOrder: 0000,2001
Boot0000* funtoo
Boot2001* EFI USB Device


%% display boot entries with bootloader files %%
%% "d4e17079-..." is /dev/sda1's /dev/disk/by-partuuid/ entry %%
# efibootmgr -v
BootCurrent: 0000
Timeout: 0 seconds
BootOrder: 0000,2001
Boot0000* funtoo
HD(1,GPT,d4e17079-d8a8-412b-9cc6-24950f31b263,0x800,0x82000)/File(\EFI\funtoo\shimx64.efi)
Boot2001* EFI USB Device RC


%% create boot entry %%
# efibootmgr -c -d /dev/sda -p 1 -L fedusr -l '\EFI\Boot\bootx64.efi'
BootCurrent: 0000
Timeout: 0 seconds
BootOrder: 0001,0000,2001
Boot0000* funtoo
Boot2001* EFI USB Device
Boot0001* fedusr


%% display boot entries with bootloader files %%
# efibootmgr -v
BootCurrent: 0000
Timeout: 0 seconds
BootOrder: 0001,0000,2001
Boot0000* funtoo
HD(1,GPT,d4e17079-d8a8-412b-9cc6-24950f31b263,0x800,0x82000)/File(\EFI\funtoo\shimx64.efi)
Boot0001* fedusr
HD(1,GPT,d4e17079-d8a8-412b-9cc6-24950f31b263,0x800,0x82000)/File(\EFI\Boot\bootx64.efi)
Boot2001* EFI USB Device RC
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