Currently I have the entire disk /dev/sda formatted as ext4, and installed Gentoo. (There is no MBR, no partition at all. )But finally, I can't install GRUB on it, because it seems like GRUB needs to write to MBR. # grub-install /dev/sdaUnknown partition table signatureUnknown partition table signatureUnknown partition table signatureUnknown partition table signatureUnknown partition table signatureThe file /boot/grub/stage1 not read correctly. neither does grub work,  # grubgrub> root (hd0) Filesystem type unknown, using whole diskgrub> setup (hd0) Error 17: Cannot mount selected partitionAny way can I install GRUB into the /dev/sda without MBR?P.S. The /boot directory and grub.conf files: # tree /boot /boot|-- boot -> .|-- grub|   |-- default|   |-- device.map|   |-- e2fs_stage1_5|   |-- fat_stage1_5|   |-- ffs_stage1_5|   |-- grub.conf|   |-- iso9660_stage1_5|   |-- jfs_stage1_5|   |-- menu.lst -> grub.conf|   |-- minix_stage1_5|   |-- reiserfs_stage1_5|   |-- splash.xpm.gz|   |-- stage1|   |-- stage2|   |-- stage2_eltorito|   |-- ufs2_stage1_5|   |-- vstafs_stage1_5|   `-- xfs_stage1_5`-- kernel-2.6.36-gentoo-r5# cat /boot/grub/grub.confdefault 0timeout 30splashimage=(hd0)/boot/grub/splash.xpm.gztitle Gentoo Linux 2.6.36-r5root (hd0)kernel /boot/kernel-2.6.36-gentoo-r5 root=/dev/sdatitle Gentoo Linux 2.6.36-r5 Rescuekernel /boot/kernel-2.6.36-gentoo-r5 root=/dev/sda init=/bin/bb# cat /boot/grub/devices(fd0)   /dev/fd0(hd0)   /dev/sda
How to install GRUB to a whole ext4 disk without partition table?
boot;grub legacy
The BIOS reads the first sector (512 bytes) of the disk and branches into it. If your disk contains PC-style partitions, the first sector also contains the partition table. If your disk contains a single filesystem, the first sector contains whatever the filesystem decides to put there. In the case of ext[234] (and many other filesystems), the first sector is reserved for the bootloader (and is initially zeroed out). You can install Grub on /dev/sda.That being said, there are occasional BIOSes that refuse to boot from a device that don't contain a partition table. (But there are also BIOSes that refuse to boot from some external devices if they do contain a partition table!) If you have one of these BIOSes, you'll have to create a partition table.Even if a partition table is not necessary, it's recommended. You only waste a few kilobytes, and gain readability under many non-Linux OSes and less surprise for any co-sysadmin. If you accidentally plug your disk into a machine running Windows, it might suggest you to reformat the disk if it doesn't see a partition table, whereas it'll just complain it can't read the data if it sees a partition table with a partition type it doesn't recognize.  In fact, the first block, I think, where a block is 1kB, 2kB or 4kB depending on the options passed to mkfs. 