[SOLVED] Booting from SD card

Massimo B. · Posted: Tue Oct 18, 2016 7:01 am Post subject: [SOLVED] Booting from SD card

Hi,

I can't get some grub2 booting from SD card.
Background is that I like to put the bootloader and the GPG-encrypted LUKS key on the SD card. The root system is stored on some large btrfs-on-luks. So I have the local harddrive as one huge luks-encrypted blockdevice. Booting requires 2 security levels that is the SD-Card (with bootloader and encrypted KEY file) and the GPG password to decrypt the KEY.

Installing grub2 on a USB pendrive, it works fine:

NeddySeagoon · Posted: Tue Oct 18, 2016 9:16 am Post subject:

Massimo B.,

Massimo B. · Posted: Tue Oct 18, 2016 9:19 am Post subject:

It just skips very early and turns over to the default boot device as if there is no SD card inserted. No GRUB menu appearing. I would just guess that the hardware cannot boot from SD card if it wouldn't work successfully with the sysresccd image.
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NeddySeagoon · Posted: Tue Oct 18, 2016 9:32 am Post subject:

Massimo B.

How is the MMC card partitioned and what filesystems does it contain?
Are you using BIOS or EFI mode?
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Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

Massimo B. · Posted: Tue Oct 18, 2016 10:00 am Post subject:

I format the SD card exactly like the USB pendrive I showed above. It works on USB but not on the SD-Card.
Currently I copied that sysresccd iso image via dd on that SD, so this does not seem to have a valid partition map but some ISO 9660. But it is booting without issues.

I just prefer the SD-Card over USB pendrive as security key, because of its small form factor, fitting in my portemonnaie.
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Massimo B. · Posted: Mon Nov 07, 2016 2:44 pm Post subject:

Not a single idea why booting from SD with the ISO 9660 works, but not with grub and msdos or gpt partition table?
How does ISO 9660 boot, is there grub also installed in that filesystem? Can I make my own SD-card like that?
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HP ZBook Power 15.6" G8 i7-11800H|HP EliteDesk 800G1 i7-4790|HP Compaq Pro 6300 i7-3770

snkmoorthy · Guru Joined: 19 Nov 2002 Posts: 376

may be you need to enable the 'boot' flag on the partition. Some BIOSes look for that specifically.(In fdisk use the 'a' option)

Massimo B. · Posted: Mon Nov 14, 2016 10:09 am Post subject:

I solved it, somehow I needed to use --force for grub-install as grub was not able to "embed" on the SD drive, no matter how much space I left in front of the first partition.
_________________
HP ZBook Power 15.6" G8 i7-11800H|HP EliteDesk 800G1 i7-4790|HP Compaq Pro 6300 i7-3770

NeddySeagoon · Posted: Mon Nov 14, 2016 10:43 am Post subject:

Massimo B.

--force makes grub use block lists to load itself. The block list is written when grub is installed to the MBR.
If you ever update grub on the SD card, you must reinstall it to the MBR too or the block lists will not point to the updated grub.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

Massimo B. · Posted: Mon Nov 14, 2016 12:47 pm Post subject:

Why do I need --force here at all, what about that blocklist mode and how can I avoid it?
As this is working:

NeddySeagoon · Posted: Mon Nov 14, 2016 3:06 pm Post subject:

Massimo B.,