readme

PC BIOS Boot Manager _within_ the Master Boot Record (MBR) Displays list of partitions and let user

mbrbm (Master Boot Record Boot Manager)

   [1]Logo of mbrbm
     __________________________________________________________________

Table of contents:

    1. [2]News
    2. [3]Summary
          + [4]About
          + [5]Project goals
    3. [6]License
    4. [7]Documentation
          + [8]Requirements
          + [9]Installation, uninstallation and configuration
          + [10]Frequently asked questions (FAQ)
          + [11]Useful hints and advices
          + [12]Important notices and limitations
          + [13]Troubleshooting
    5. [14]Screenshots
    6. [15]Features
    7. [16]Download
    8. [17]ToDo
    9. [18]Contacts
   10. [19]Links
     __________________________________________________________________

News

   October 23, 2006

   mbrbm version 1.0 has been released

Summary

  About

   mbrbm is yet another boot loader which fits into first sector of an HDD
   (MBR). It allows to choose which partition to boot and is intended to
   replace an MBR coming with DOS/Windows. It may boot any primary
   partition boot record below cylinder 1024.

   mbrbm is not an operating system loader. I can not boot Linux or
   Windows directly (thus it is not a replacement of LILO/GRUB/ntldr for
   example), but it can boot an appropriate loader from a boot record of a
   particular partition (again LILO/GRUB/ntldr for instance).

   mbrbm's functionality is completely implemented _WITHIN_ the Master
   Boot Record. It is written in nasm (x86 assembler). On boot it displays
   a primary partition list with type/size and let the user choose the
   booting partition by selecting it by number-keystroke. At timeout the
   active partition is bootet. With no interaction it does exactly what a
   standard DOS/Windows9x/ME (fdisk /mbr) MBR does.

   Restrictions are that it cannot boot via LBA (partitions above cylinder
   1024) and extended partitions. It's compatible with DOS,
   Windows(9x,ME,NT,2K,XP,2003,Vista), Lilo, Grub, xBSD, ... partition
   boot records.

   My usage of mbrbm is primary for servers on which i always put a
   FreeDOS partition for basic diagnostic and recovery tasks, regardless
   whether the server is running Linux, xBSD or Windows. There are no
   driver troubles with DOS accessing the disks, raid, ... the BIOS takes
   care of it. There are lots of good tools for hardware diagnostic,
   partition recovery and the like running on FreeDOS.

   With mbrbm i have always a spare boot option without complicated boot
   manager setups - the standard boot method setup of the target OS living
   in the second or third partition works out of the box with the standard
   installation procedure of the server OS - no hassle with lilo, grub or
   BOOT.INI configuration after the installation. And the best part is
   that i need no documentation of a complicated setup for the other
   system administrators. This scenario did save my life a few times.
   Therefore i share it here.

  Project goals

     * To maintain a boot loader which fits into master boot record (first
       sector of HDD 512 bytes from which only 438 bytes can be used for
       code, some place is occupied by VolumeID, partition table and a
       magic number) of a hard disk. There are lot of boot managers
       occupying almost whole track #0 of cylinder #0. I don't want to
       compete with them. The unused sectors on track #0 are also often
       used by recovery software, so the chance to break something is
       relatively high
     * To allow a user to choose which operating system to boot with a
       simple textual interface (no graphics, icons, mouse, etc.) with
       timeout to active partition
     * To support as many operating systems as possible
     * No configuration software need
     * No installation software need - just copy the 438 byte of code to
       disk - that's all
     * THE WHOLE PROJECT DELIVERS 438 (four-hundred-and-thirty-seven)
       BYTES OF CODE

License

   GPL V2.

Documentation

  Requirements

    1. Run requirement:
       IBM PC-compatible computer with INT13 BIOS (99.99999% of all
       computers - even very old ones are Ok)
    2. Compile requirement:
       The mbrbm MBR could be compiled on Linux and BSD with nasm
    3. Installation requirement:
       Standard Linux, xBSD (dd) or FreeDOS (FDISK) tools (can boot these
       from CD at installtime)

  Installation and uninstallation

   The mbrbm project is intended to be used by advanced users on their
   desktop computers. If you have several operating systems and want to be
   able to boot either of them, you may use mbrbm. It is a replacement of
   the default boot loader in MBR which for instance could be written
   there by Microsoft Windows installation. The whole installation is just
   the writing the very first 438 bytes of the first harddisk with the
   assembled code of mbrbm.S - the MBR. THERE IS NO CONFIGURATION -
   INSTALLATION -> DONE.

FULL BACKUP IS HIGHLY RECOMMENDED
PROCEED ONLY IF YOU REALLY KNOW WHAT YOU'RE DOING HERE
YOU NEED A WORKING PARTITION BOOT SECTOR FOR EVERY
OPERATING SYSTEM YOU WANT TO BOOT

Compilation of the mbr (or take the compiled version for the distribution archiv
e):
[root@mbrbm /etc]# cd /etc
[root@mbrbm /etc]# nasm mbrbm.S -o mbrbm.bin

Installation with Linux on first IDE Harddisk (use /dev/sda for SCSI):
[root@mbrbm /etc]# cd /etc
[root@mbrbm /etc]# dd if=/dev/hda of=hda.mbr bs=1b count=1
[root@mbrbm /etc]# dd if=mbrbm.bin of=hdambrbm.mbr bs=1 count=438
[root@mbrbm /etc]# dd if=hda.mbr bs=1 skip=438 count=74 >>hdambrbm.mbr
[root@mbrbm /etc]# dd if=hdambrbm.mbr of=/dev/hda bs=1b count=1
[root@mbrbm /etc]# # KEEP THE FILE /etc/hda.mbr AS BACKUP OF ORIGINAL MBR

Deinstallation with Linux on first IDE Harddisk:
[root@mbrbm /etc]# dd if=/etc/hda.mbr of=/dev/hda bs=1b count=1

Installation with FreeDOS on first Harddisk:
C:\> C:
C:\> CD \
C:\> FDISK /SMBR 1
C:\> COPY BOOT.MBR hda.mbr
C:\> COPY mbrbm.bin BOOT.MBR
C:\> FDISK /AMBR 1
C:\> : KEEP THE FILE C:\hda.mbr AS BACKUP OF ORIGINAL MBR

Deinstallation with FreeDOS on first Harddisk:
C:\> COPY hda.mbr BOOT.MBR
C:\> FDISK /AMBR 1

  Frequently asked questions (FAQ)

   Q1: Yet another boot manager? What are the advantages of mbrbm over
   others?
   A1: mbrbm is first choice if you want an operating system independent
   boot manager without configuraton. Unlike grub, lilo or ntldr(BOOT.INI)
   mbrbm does not need a working (booting) operating system partition.
   It's whole functionality is within the MBR. It will not fail to boot
   your secondary operating system if you completely destroy the primary.
   In fact there is no more a primary or secondary OS. In effect
   complexity is dramatically reduced from the bootstrapping system. The
   OS's on the system are just installed with their default booting
   schema. No configuration afterwards is needed. No hassle with
   lilo.conf, grub.conf or confusing BOOT.INI magic.

   Consider a situation when you have 2 primary partitions: one with
   Windows XP and another one with Linux. What are your options to boot
   either of them? Using LILO which is able to boot both OSes you will
   loose an ability to normally boot a system to Windows XP if you
   completely fill Linux partition by zeroes. The same with standard DOS +
   loadlin or Windows ntldr + BOOT.INI executables. In this case you
   should not break Windows partition otherwise you will loose an ability
   to load Linux.

   Of course there are many other third-party managers which are not parts
   of the operating systems above. Several alternatives to mbrbm are
   listed in [20]Links section. However almost all of them require either
   separate partition (like OS/2 boot manager) or a directory in FAT
   partition (like PQBoot) or occupy almost the whole track #0 on cylinder
   #0 (it is unused on most systems). mbldr (Master Boot LoaDeR) needs to
   be configured, what has to be redone when booting partitions are added
   or moved. bm uses also parts of track #0 - nuni can only boot IDE
   drives and needs source code configuration. All these solutions add
   complexity to the bootstrap setup - complexity is the biggest enemy of
   availabilty and security! mbrbm requires only the space which is
   reserved for the master boot loader by definition, only 438 bytes of
   1st sector are used.

   Nevertheless there are some drawbacks: the extreme simplicity leads to
   low quality of user interface (only text with minimum usability), less
   features could be included: no lba and extended partitions can be
   bootet.

   Q2: Compilation breaks with "error: argument to ORG should be numeric"
   message in mbrbm.err. What am I doing wrong?
   A2: The version of nasm required to build mbrbm is greater or equal to
   0.98.36. Release .35 which is often shipped in many popular (but rather
   old) distributions could not be used.

   Q3: When trying to update the MBR contents on /dev/ad0 under BSD I get
   "Operation not permitted" error. How to overcome this?
   A3: This protection of BSD is active because hard disk is available for
   writing at the moment. Try to issue a command "sysctl
   kern.geom.debugflags=16" to temporarily disable it. Update your MBR and