the stage1 and stage1.5 code that is actually executed at boot time are not visible as files.
(The grub install copies /boot/grub/stage1 and possibly /boot/grub/e2fs_stage1_5 to new disk
locations.) If /boot is in an ext2/3 filesystem, I think 'stage2' is executed from there.
I'm sure you've probably seen this in the 0.97 Grub Manual:
Code:
Chapter 10: GRUB image files 29
10 GRUB image files
GRUB consists of several images: two essential stages, optional stages called Stage 1.5, one
image for bootable CD-ROM, and two network boot images. Here is a short overview of
them. See Appendix D [Internals], page 75, for more details.
‘stage1’ This is an essential image used for booting up GRUB. Usually, this is embedded
in an MBR or the boot sector of a partition. Because a PC boot sector is 512
bytes, the size of this image is exactly 512 bytes.
All ‘stage1’ must do is to load Stage 2 or Stage 1.5 from a local disk. Because
of the size restriction, ‘stage1’ encodes the location of Stage 2 (or Stage 1.5)
in a block list format, so it never understand any filesystem structure.
‘stage2’ This is the core image of GRUB. It does everything but booting up itself.
Usually, this is put in a filesystem, but that is not required.
‘e2fs_stage1_5’
‘fat_stage1_5’
‘ffs_stage1_5’
‘jfs_stage1_5’
‘minix_stage1_5’
‘reiserfs_stage1_5’
‘vstafs_stage1_5’
‘xfs_stage1_5’
These are called Stage 1.5, because they serve as a bridge between ‘stage1’
and ‘stage2’, that is to say, Stage 1.5 is loaded by Stage 1 and Stage 1.5 loads
Stage 2. The difference between ‘stage1’ and ‘*_stage1_5’ is that the former
doesn’t understand any filesystem while the latter understands one filesystem
(e.g. ‘e2fs_stage1_5’ understands ext2fs). So you can move the Stage 2 image
to another location safely, even after GRUB has been installed.
While Stage 2 cannot generally be embedded in a fixed area as the size is so
large, Stage 1.5 can be installed into the area right after an MBR, or the boot
loader area of a ReiserFS or a FFS.
If you did what is a fairly typical install of Linux into an ext2/3 filesystem with a small
'/boot' ext2/3 partition, you would have: the 'stage1' in the MBR, sector0; and 'e2fs_stage1_5'
in the "the area right after an MBR". On my system it's not there. I don't know where it is,
but by virtue of the "block list", 'stage1' can find and pass control to it. 'e2fs_stage1_5'
understands the ext2/3 filesystem, so it can easily find files.
If you want the sector address from the beginning of the filesystem (i.e. partition), it's the
blockaddress from debugfs times 8, as the blocksize is 4096 (on my system) and a sector is 512 bytes...
Code:
[root@athlon4k6 ~]# debugfs -R 'stat grub/stage2' /dev/sda1
debugfs 1.40.2 (12-Jul-2007)
Inode: 29255 Type: regular Mode: 0644 Flags: 0x0 Generation: 1083286271
User: 0 Group: 0 Size: 104924
File ACL: 9190 Directory ACL: 0
Links: 1 Blockcount: 224
Fragment: Address: 0 Number: 0 Size: 0
ctime: 0x46a13081 -- Fri Jul 20 18:00:33 2007
atime: 0x484948a5 -- Fri Jun 6 10:24:37 2008
mtime: 0x46a13081 -- Fri Jul 20 18:00:33 2007
BLOCKS:
(0-11):34807-34818, (IND):34819, (12-25):34820-34833
TOTAL: 27
So, starting sector, relative to the start of the partition is 34807 * 8 = 278,456.
To find the absolute sector, you need to know where the partition starts.
Code:
[root@athlon4k6 ~]# fdisk -lu /dev/sda
Disk /dev/sda: 500.1 GB, 500106780160 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976771055 sectors
Units = sectors of 1 * 512 = 512 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 63 2104514 1052226 83 Linux
/dev/sda2 2104515 136327589 67111537+ 83 Linux
/dev/sda4 270550665 976768064 353108700 5 Extended
/dev/sda5 270550728 291515489 10482381 8e Linux LVM
/dev/sda6 291515553 312480314 10482381 8e Linux LVM
/dev/sda7 312480378 333445139 10482381 8e Linux LVM
/dev/sda8 333445203 354409964 10482381 8e Linux LVM
/dev/sda9 354410028 356546609 1068291 83 Linux
/dev/sda10 356546673 456567299 50010313+ 8e Linux LVM
/dev/sda11 456567363 556587989 50010313+ 8e Linux LVM
/dev/sda12 556588053 656608679 50010313+ 8e Linux LVM
/dev/sda13 656608743 756629369 50010313+ 8e Linux LVM
/dev/sda14 756629433 856650059 50010313+ 8e Linux LVM
/dev/sda15 856650123 956670749 50010313+ 8e Linux LVM
So, in this case /boot/grub/stage2 would start at 63 + 278,456 = 278,519.
And here it is accessed by absolute address.
Code:
[root@athlon4k6 ~]# dd if=/dev/sda bs=512 count=1 skip=278519 | xxd | head
1+0 records in
1+0 records out
512 bytes (512 B) copied, 9.4696e-05 s, 5.4 MB/s
0000000: 5256 be03 81e8 2801 5ebf f881 668b 2d83 RV....(.^...f.-.
0000010: 7d04 000f 84ca 0080 7cff 0074 3e66 8b1d }.......|..t>f..
0000020: 6631 c0b0 7f39 4504 7f03 8b45 0429 4504 f1...9E....E.)E.
0000030: 6601 05c7 0410 0089 4402 6689 5c08 c744 f.......D.f.\..D
0000040: 0600 7050 6631 c089 4404 6689 440c b442 ..pPf1..D.f.D..B
0000050: cd13 0f82 9f00 bb00 70eb 5666 8b05 6631 ........p.Vf..f1
0000060: d266 f734 8854 0a66 31d2 66f7 7404 8854 .f.4.T.f1.f.t..T
0000070: 0b89 440c 3b44 087d 748b 042a 440a 3945 ..D.;D.}t..*D.9E
0000080: 047f 038b 4504 2945 0466 0105 8a54 0dc0 ....E.)E.f...T..
0000090: e206 8a4c 0afe c108 d18a 6c0c 5a52 8a74 ...L......l.ZR.t
And here it is accessed as a file.
Code:
[root@athlon4k6 ~]# xxd /boot/grub/stage2 | head
0000000: 5256 be03 81e8 2801 5ebf f881 668b 2d83 RV....(.^...f.-.
0000010: 7d04 000f 84ca 0080 7cff 0074 3e66 8b1d }.......|..t>f..
0000020: 6631 c0b0 7f39 4504 7f03 8b45 0429 4504 f1...9E....E.)E.
0000030: 6601 05c7 0410 0089 4402 6689 5c08 c744 f.......D.f.\..D
0000040: 0600 7050 6631 c089 4404 6689 440c b442 ..pPf1..D.f.D..B
0000050: cd13 0f82 9f00 bb00 70eb 5666 8b05 6631 ........p.Vf..f1
0000060: d266 f734 8854 0a66 31d2 66f7 7404 8854 .f.4.T.f1.f.t..T
0000070: 0b89 440c 3b44 087d 748b 042a 440a 3945 ..D.;D.}t..*D.9E
0000080: 047f 038b 4504 2945 0466 0105 8a54 0dc0 ....E.)E.f...T..
0000090: e206 8a4c 0afe c108 d18a 6c0c 5a52 8a74 ...L......l.ZR.t
[root@athlon4k6 ~]#
