10. GRUB image files

GRUB consists of several images: two essential stages, optional stages called Stage 1.5, and two network boot images. Here is a short overview of them. See section E. Hacking GRUB, for more details.

`stage1'

This is an essential image used for booting up GRUB. Usually, this is embedded in a 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. This does all things 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 the purpose is 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 but the latter does an filesystem (e.g. `e2fs_stage1_5' understands ext2fs). So you can move the location of Stage 2 to another 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 a MBR, or the boot loader area of a ReiserFS or a FFS.

`nbgrub'

This is a network boot image for the Network Image Proposal used by some network boot loaders, such as Etherboot. This is mostly the same as Stage 2, but this also sets up a network and loads a configuration file from the network.

`pxegrub'

This is another network boot image for the Preboot Execution Environment used by several Netboot ROMs. This is identical to `nbgrub', except for the format.