Linux grub: Difference between revisions

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[[Kategorie:Linux|Grub]]
[[Category:Linux|Grub]]
[[Kategorie:Grub|Linux]]
[[Category:Grub|Linux]]
=grub rescue>=
=grub rescue>=
The problem:
The problem:
<source lang=bash>
<syntaxhighlight lang=bash>
...
...
Entering rescue mode...                                                         
Entering rescue mode...                                                         
grub rescue>         
grub rescue>         
</source>
</syntaxhighlight>




Line 13: Line 13:


Find your devices:
Find your devices:
<source lang=bash>
<syntaxhighlight lang=bash>
grub rescue> ls
grub rescue> ls
</source>
</syntaxhighlight>


===Find the directory where the normal.mod file resides===
===Find the directory where the normal.mod file resides===
In this example we have LVM and the /boot/grub is in VG vg-root and the LV lv-root.
In this example we have LVM and the /boot/grub is in VG vg-root and the LV lv-root.
<source lang=bash>
<syntaxhighlight lang=bash>
grub rescue> ls (lvm/vg--root-lv--root)/boot/grub/i386-pc
grub rescue> ls (lvm/vg--root-lv--root)/boot/grub/i386-pc
... normal.mod ...
... normal.mod ...
</source>
</syntaxhighlight>


===Set the prefix to the right place===
===Set the prefix to the right place===
<source lang=bash>
<syntaxhighlight lang=bash>
grub rescue> set prefix=(lvm/vg--root-lv--root)/boot/grub
grub rescue> set prefix=(lvm/vg--root-lv--root)/boot/grub
</source>
</syntaxhighlight>


===Now you can load and start the module called "normal"===
===Now you can load and start the module called "normal"===
<source lang=bash>
<syntaxhighlight lang=bash>
grub rescue> insmod normal
grub rescue> insmod normal
grub rescue> normal
grub rescue> normal
</source>
</syntaxhighlight>


If the menu not occurs you get something like this:
If the menu not occurs you get something like this:
<source lang=bash>
<syntaxhighlight lang=bash>
                   GNU GRUB  version 1.99,5.11.0.175.2.0.0.42.2
                   GNU GRUB  version 1.99,5.11.0.175.2.0.0.42.2


Line 44: Line 44:


grub>
grub>
</source>
</syntaxhighlight>


==Normal grub is bootet, now start the Kernel==
==Normal grub is bootet, now start the Kernel==
Example for LVM:
===Example for LVM===
<source lang=bash>
<syntaxhighlight lang=bash>
insmod gzio
insmod gzio
insmod part_msdos
insmod part_msdos
Line 56: Line 56:
linux  /boot/vmlinuz-4.4.0-53-generic root=/dev/mapper/vg--root-lv--root ro   
linux  /boot/vmlinuz-4.4.0-53-generic root=/dev/mapper/vg--root-lv--root ro   
initrd  /boot/initrd.img-4.4.0-53-generic
initrd  /boot/initrd.img-4.4.0-53-generic
</source>
</syntaxhighlight>


Example for ZFS-Root:
===Example for ZFS-Root===
<source lang=bash>
<syntaxhighlight lang=bash>
insmod gzio
insmod gzio
insmod part_msdos
insmod part_msdos
insmod part_gpt
insmod zfs
insmod zfs
set root='hd0,msdos4'
set root='hd0,msdos4'
linux  /ROOT/ubuntu-15.04@/boot/vmlinuz-4.4.0-57-generic root=ZFS=rpool/ROOT/ubuntu-15.04 boot=zfs zfs_force=1 ro  quiet splash nomdmonddf nomdmonisw $vt_handoff
linux  /ROOT/ubuntu-15.04@/boot/vmlinuz-4.4.0-57-generic root=ZFS=rpool/ROOT/ubuntu-15.04 boot=zfs zfs_force=1 ro  quiet splash nomdmonddf nomdmonisw $vt_handoff
initrd  /ROOT/ubuntu-15.04@/boot/initrd.img-4.4.0-57-generic
initrd  /ROOT/ubuntu-15.04@/boot/initrd.img-4.4.0-57-generic
</source>
</syntaxhighlight>
 
===Example for ZFS-Root on GPT with known nothing about the location of kernel and initrd===
<br><pre><TAB> means press tab key.</pre>
<syntaxhighlight lang=bash>
grub> insmod gzio
grub> insmod part_gpt
grub> insmod part_msdos
grub> insmod zfs
grub> ls (<TAB>
Possible devices are:
 
proc memdisk hd0 hd1 hd2
</syntaxhighlight>
So we have several disks. Let us see what partitions we have:
<syntaxhighlight lang=bash highlight="5">
grub> ls (hd0<TAB>
Possible partitions are:
Device hd0: No known filesystem detected - Sector size 512B - Total size 5242880KiB
        Partition hd0,gpt1: Filesystem type fat - Label `EFI', UID 4711-6C33 - Partition start at 1024KiB - Total size 524288KiB
        Partition hd0,gpt3: Filesystem type zfs - Label `bpool' - Last modification time 2024-07-01 04:36:00 Monday, UUID 001702272575c1blabla - Partition start at 525312KiB - Total size 4717551.5KiB
        Partition hd0,gpt5: No known filesystem detected - Partition start at 24KiB - Total size 1000KiB
</syntaxhighlight>
Now we know more about the possible partitions and due to the filesystem type and the labels we can see hd0,gpt3 would be a good start to look at. But the Last modification time looks a little old. We will see (Tell me why I don't like Mondays...).
<syntaxhighlight lang=bash>
grub> ls (hd0,gpt3)/<TAB>
Possible files are:
@/ BOOT/
</syntaxhighlight>
You can use tab until you found the right dataset and than /@/ at the end:
<syntaxhighlight lang=bash>
grub> ls (hd0,gpt3)/BOOT/ubuntu_flupdy/@/
efi grub
grub>
</syntaxhighlight>
Soooo... now we know, our dataset was not properly mounted when configuring grub. But we migrated from all in rpool to rpool and bpool. Maybe we have a snapshot on rpool where still a /boot with a kernel dangles around...
<syntaxhighlight lang=bash highlight="5">
grub> ls (hd1,gpt1)/ROOT/<TAB>
...
@zfs-auto-snap_daily-2024-06-31-06.42.00--7d/
@zfs-auto-snap_daily-2024-06-30-06.42.00--7d/
@zfs-auto-snap_daily-2024-06-29-06.43.00--7d/
@zfs-auto-snap_daily-2024-06-28-06.42.00--7d/
@zfs-auto-snap_daily-2024-06-27-06.44.00--7d/
@zfs-auto-snap_daily-2024-06-26-06.42.00--7d/
...
grub> ls (hd1,gpt1)/ROOT/ubuntu_flupdy/@zfs-auto-snap_daily-2024-06-29-06.43.00--7d/boot/
vmlinuz-6.5.0-45-generic ...
</syntaxhighlight>
YES! That is what we searched for!
<syntaxhighlight lang=bash>
set root='hd1,gpt1'
linux  "/ROOT/ubuntu_flupdy/@zfs-auto-snap_daily-2024-06-29-06.43.00--7d/boot/vmlinuz-6.5.0-45-generic" root=ZFS="rpool/ROOT/ubuntu_flupdy" ro single nomodeset dis_ucode_ldr text console=tty0 console=ttyS0,115200n8 nosplash init_on_alloc=0
initrd  "/ROOT/ubuntu_flupdy/@zfs-auto-snap_daily-2024-06-29-06.43.00--7d/boot/initrd.img-6.5.0-45-generic"
boot
</syntaxhighlight>
Here we go!

Latest revision as of 12:24, 1 August 2024

grub rescue>

The problem: 

...
Entering rescue mode...                                                         
grub rescue>


Get into the normal grub

Find your devices: 

grub rescue> ls

Find the directory where the normal.mod file resides

In this example we have LVM and the /boot/grub is in VG vg-root and the LV lv-root. 

grub rescue> ls (lvm/vg--root-lv--root)/boot/grub/i386-pc
... normal.mod ...

Set the prefix to the right place

grub rescue> set prefix=(lvm/vg--root-lv--root)/boot/grub

Now you can load and start the module called "normal"

grub rescue> insmod normal
grub rescue> normal

If the menu not occurs you get something like this: 

                  GNU GRUB  version 1.99,5.11.0.175.2.0.0.42.2

   Minimal BASH-like line editing is supported. For the first word, TAB
   lists possible command completions. Anywhere else TAB lists possible
   device or file completions.

grub>

Normal grub is bootet, now start the Kernel

Example for LVM

insmod gzio
insmod part_msdos
insmod lvm
insmod ext2
set root='lvmid/KAlPF4-Qb8I-Sx41-10cC-lACw-Msoh-3qEohv/pmE9Nt-rLG3-FlNM-CwOT-hy42-gSnm-fZSn3l'
linux   /boot/vmlinuz-4.4.0-53-generic root=/dev/mapper/vg--root-lv--root ro  
initrd  /boot/initrd.img-4.4.0-53-generic

Example for ZFS-Root

insmod gzio
insmod part_msdos
insmod part_gpt
insmod zfs
set root='hd0,msdos4'
linux   /ROOT/ubuntu-15.04@/boot/vmlinuz-4.4.0-57-generic root=ZFS=rpool/ROOT/ubuntu-15.04 boot=zfs zfs_force=1 ro  quiet splash nomdmonddf nomdmonisw $vt_handoff
initrd  /ROOT/ubuntu-15.04@/boot/initrd.img-4.4.0-57-generic

Example for ZFS-Root on GPT with known nothing about the location of kernel and initrd


<TAB> means press tab key.
grub> insmod gzio
grub> insmod part_gpt
grub> insmod part_msdos
grub> insmod zfs
grub> ls (<TAB>
Possible devices are:

 proc memdisk hd0 hd1 hd2

So we have several disks. Let us see what partitions we have: 

grub> ls (hd0<TAB>
Possible partitions are:
Device hd0: No known filesystem detected - Sector size 512B - Total size 5242880KiB
        Partition hd0,gpt1: Filesystem type fat - Label `EFI', UID 4711-6C33 - Partition start at 1024KiB - Total size 524288KiB
        Partition hd0,gpt3: Filesystem type zfs - Label `bpool' - Last modification time 2024-07-01 04:36:00 Monday, UUID 001702272575c1blabla - Partition start at 525312KiB - Total size 4717551.5KiB
        Partition hd0,gpt5: No known filesystem detected - Partition start at 24KiB - Total size 1000KiB

Now we know more about the possible partitions and due to the filesystem type and the labels we can see hd0,gpt3 would be a good start to look at. But the Last modification time looks a little old. We will see (Tell me why I don't like Mondays...). 

grub> ls (hd0,gpt3)/<TAB>
Possible files are:
 @/ BOOT/

You can use tab until you found the right dataset and than /@/ at the end: 

grub> ls (hd0,gpt3)/BOOT/ubuntu_flupdy/@/
efi grub
grub>

Soooo... now we know, our dataset was not properly mounted when configuring grub. But we migrated from all in rpool to rpool and bpool. Maybe we have a snapshot on rpool where still a /boot with a kernel dangles around... 

grub> ls (hd1,gpt1)/ROOT/<TAB>
...
@zfs-auto-snap_daily-2024-06-31-06.42.00--7d/
@zfs-auto-snap_daily-2024-06-30-06.42.00--7d/
@zfs-auto-snap_daily-2024-06-29-06.43.00--7d/
@zfs-auto-snap_daily-2024-06-28-06.42.00--7d/
@zfs-auto-snap_daily-2024-06-27-06.44.00--7d/
@zfs-auto-snap_daily-2024-06-26-06.42.00--7d/
...
grub> ls (hd1,gpt1)/ROOT/ubuntu_flupdy/@zfs-auto-snap_daily-2024-06-29-06.43.00--7d/boot/
vmlinuz-6.5.0-45-generic ...

YES! That is what we searched for! 

set root='hd1,gpt1'
linux   "/ROOT/ubuntu_flupdy/@zfs-auto-snap_daily-2024-06-29-06.43.00--7d/boot/vmlinuz-6.5.0-45-generic" root=ZFS="rpool/ROOT/ubuntu_flupdy" ro single nomodeset dis_ucode_ldr text console=tty0 console=ttyS0,115200n8 nosplash init_on_alloc=0
initrd  "/ROOT/ubuntu_flupdy/@zfs-auto-snap_daily-2024-06-29-06.43.00--7d/boot/initrd.img-6.5.0-45-generic"
boot

Here we go!

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