On 08/06/2015 02:19 PM, Chris Murphy wrote:
> stage 1 cannot point to another drive at all. It's sole purpose is to
> find stage 2, which must be on the same drive. Stage 1.5 is optional,
> and I've never seen it get used on Linux, mainly because in the time
> of GRUB legacy, I never encountered an installer that supported XFS
> for /boot.
Grub's documentation is slightly unclear about that. Here's a system
where /boot is part of a RAID1 set on /dev/vdc1 and /dev/vdd1:
[root at localhost ~]# cat /boot/grub/device.map
# this device map was generated by anaconda
(hd0) /dev/vda
(hd2) /dev/vdc
(hd3) /dev/vdd
[root at localhost ~]# grub
Probing devices to guess BIOS drives. This may take a long time.
GNU GRUB version 0.97 (640K lower / 3072K upper memory)
[ Minimal BASH-like line editing is supported. For the first
word, TAB
lists possible command completions. Anywhere else TAB lists the
possible
completions of a device/filename.]
grub> root (hd2,0)
root (hd2,0)
Filesystem type is ext2fs, partition type 0xfd
grub> setup (hd0)
setup (hd0)
Checking if "/boot/grub/stage1" exists... no
Checking if "/grub/stage1" exists... yes
Checking if "/grub/stage2" exists... yes
Checking if "/grub/e2fs_stage1_5" exists... yes
Running "embed /grub/e2fs_stage1_5 (hd0)"... 27 sectors are embedded.
succeeded
Running "install /grub/stage1 d (hd0) (hd0)1+27 p
(hd2,0)/grub/stage2 /grub/grub.conf"... succeeded
Done.
grub>
I believe the final line can be interpreted as:
0: install: the install command
1: /grub/stage1: path to the stage1 file, relative to the root
2: d: grub will look for stage2_file at the address specified in arg 4
3: (hd0): grub will be written to the first block of (hd0), currently
mapped to /dev/vda
4: (hd0)1+27: stage1_5 has been embedded to this location. It is being
used as "stage2_file"
5: p: the first block of stage2 will be modified with the value of the
partition where stage2_file is found
6: (hd2,0)/grub/stage2:
7: /grub/grub.conf: because this arg is present and #4 is really a stage
1.5, the stage2 config file is patched with this configuration file name.
If I specify "root (hd3,0)" in the grub shell, the boot loader will
differ at 0002032, where it will refer to BIOS device 3 instead of BIOS
device 2 for the location of /grub/stage2.
--- vda.2 2015-08-06 16:05:32.039999919 -0700
+++ vda.3 2015-08-06 16:05:59.441999927 -0700
@@ -53,7 +53,7 @@
*
0001760 \0 \0 \0 \0 \0 \0 \0 \0 002 \0 \0 \0 032 \0 002
0002000 352 p " \0 \0 \0 003 002 377 377 377 \0 \0 \0 \0 \0
-0002020 002 \0 0 . 9 7 \0 377 377 \0 202 / g r u b
+0002020 002 \0 0 . 9 7 \0 377 377 \0 203 / g r u b
0002040 / s t a g e 2 / g r u b / g r
0002060 u b . c o n f \0 \0 \0 \0 \0 \0 \0 \0 \0
0002100 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0
...unless I'm mistaken. :)