  SRM Firmware Howto
  David Mosberger <mailto:davidm@azstarnet.com> and Rich Payne
  <mailto:rdp@alphalinux.org>
  v0.5.2, 5 December 1999

  This document describes how to boot Linux/Alpha using the SRM
  firmware, which is the firmware normally used to boot DEC Unix (also
  known as OSF/1 and Tru64Unix) and OpenVMS.  Sometimes, it is prefer-
  able to use MILO instead of aboot since MILO is perfectly adapted to
  the needs of Linux.  However, MILO is not always available for a par-
  ticular system, MILO does not presently have the ability to boot over
  the network (without patches) and little development work is now being
  done on MILO (for more information on MILO refer to the MILO Howto,
  available from http://www.alphalinux.org/faq/milo.html
  <http://www.alphalinux.org/faq/milo.html>).  In any case, using the
  SRM console may be  the right solution.
  ______________________________________________________________________

  Table of Contents


  1. What is SRM?

     1.1 How Does SRM Boot an OS?
     1.2 Loading The Secondary Bootstrap Loader

  2. The Raw Loader

  3. The aboot Loader

     3.1 Getting and Building aboot
     3.2 Floppy Installation
     3.3 Harddisk Installation
     3.4 CD-ROM Installation
     3.5 Building the Linux Kernel
     3.6 Booting Linux
        3.6.1 Device Naming
        3.6.2 Boot Filename
        3.6.3 Boot Flags
           3.6.3.1 Selecting the Partition of /etc/aboot.conf
     3.7 Installation Linux Distributions
        3.7.1 Installation from the Red Hat 6.0 CD
        3.7.2 Installation from the SuSE 6.1 CD
     3.8 Booting Over the Network
     3.9 Partitioning Disks
        3.9.1 What is a disklabel?
        3.9.2 Partitioning the Easy Way: a DOS Disklabel
        3.9.3 Partitioning with a BSD Disklabel

  4. Sharing a Disk With DEC Unix

     4.1 Partitioning the disk
     4.2 Installing

  5. Document History



  ______________________________________________________________________

  Unless you're interested in technical details, you may want to skip
  right to Section ``''.




  1.  What is SRM?

  SRM console is used by Alpha systems as Unix-style boot firmware.
  Tru64 Unix and OpenVMS depend on it and Linux can boot from it. You
  can recognize SRM console as a blue screen with a prompt that is
  presented to you on power-up.  If your Alpha system starts up with
  AlphaBIOS, or some other firmware, then this document is not for you.


  1.1.  How Does SRM Boot an OS?

  All versions of SRM can boot from SCSI disks and the versions for
  recent platforms, such as the Noname or AlphaStations can boot from
  floppy disks as well.  Network booting via bootp is supported.  Note
  that older SRM versions (notably the one for the Jensen) cannot boot
  from floppy disks. Booting from IDE devices is supported on newer
  platforms (DS20, DS10, DP264, UP2000 etc..).


  Booting Linux with SRM is a two step process: first, SRM loads and
  transfers control to the secondary bootstrap loader.  Then the
  secondary bootstrap loader sets up the environment for Linux, reads
  the kernel image from a disk filesystem and finally transfers control
  to Linux.


  Currently, there are two secondary bootstrap loaders for Linux: the
  raw loader that comes with the Linux kernel and aboot which is
  distributed separately.  These two loaders are described in more
  detail below.



  1.2.  Loading The Secondary Bootstrap Loader

  SRM knows nothing about filesystems or disk-partitions.  It simply
  expects that the secondary bootstrap loader occupies a consecutive
  range of physical disk sector, starting from a given offset.  The
  information on the size of the secondary bootstrap loader and the
  offset of its first disk sector is stored in the first 512 byte
  sector.  Specifically, the long integer at offset 480 stores the size
  of the secondary bootstrap loader (in 512-byte blocks) and the long at
  offset 488 gives the sector number at which the secondary bootstrap
  loader starts.  The first sector also stores a flag-word at offset 496
  which is always 0 and a checksum at offset 504.  The checksum is
  simply the sum of the first 63 long integers in the first sector.


  If the checksum in the first sector is correct, SRM goes ahead and
  reads the size sectors starting from the sector given in the sector
  number field and places them in virtual memory at address 0x20000000.
  If the reading completes successfully, SRM performs a jump to address
  0x20000000.


  2.  The Raw Loader

  The sources for this loader can be found in directory



               linux/arch/alpha/boot




  of the Linux kernel source distribution.  It loads the Linux kernel by
  reading START_SIZE bytes starting at disk offset BOOT_SIZE+512 (also
  in bytes).  The constants START_SIZE and BOOT_SIZE are defined in
  linux/include/asm-alpha/system.h.  START_SIZE must be at least as big
  as the kernel image (i.e., the size of the .text, .data, and .bss
  segments).  Similarly, BOOT_SIZE must be at least as big as the image
  of the raw bootstrap loader.  Both constants should be an integer
  multiple of the sector size, which is 512 bytes.  The default values
  are currently 2MB for START_SIZE and 16KB for BOOT_SIZE.  Note that if
  you want to boot from a 1.44MB floppy disk, you have to reduce
  START_SIZE to 1400KB and make sure that the kernel you want to boot is
  no bigger than that.


  To build a raw loader, simply type make rawboot in /usr/src/linux.
  This should produce the following files in arch/alpha/boot:


     tools/lxboot:
        The first sector on the disk.  It contains the offset and size
        of the next file in the format described above.

     tools/bootlx:
        The raw boot loader that will load the file below.

     vmlinux.nh:
        The raw kernel image consisting of the .text, .data, and .bss
        segments of the object file in /usr/src/linux/vmlinux.  The
        extension .nh indicates that this file has no object-file
        header.


  The concatenation of these three files should be written to the disk
  from which you want to boot.  For example, to boot from a floppy,
  insert an empty floppy disk in, say, /dev/fd0 and then type:


       cat tools/lxboot tools/bootlx vmlinux >/dev/fd0





  You can then shutdown the system and boot from the floppy by issuing
  the command boot dva0.


  3.  The aboot Loader

  When using the SRM firmware, aboot is the preferred way of booting
  Linux.  It supports:


  o  direct booting from various filesystems (ext2, ISO9660, and UFS,
     the DEC Unix filesystem)

  o  booting of executable object files (both ELF and ECOFF)

  o  booting compressed kernels

  o  network booting (using bootp)

  o  partition tables in DEC Unix format (which is compatible with BSD
     Unix partition tables)


  o  interactive booting and default configurations for SRM consoles
     that cannot pass long option strings



  3.1.  Getting and Building aboot

  The latest sources for aboot are available in this ftp directory
  <ftp://ftp.alphalinux.org.com/aboot>.  The description in this manual
  applies to aboot version 0.5 or newer. Please note that many
  distributions ship aboot with them so downloading aboot from this
  directory is probably unnessesary.


  Once you downloaded and extracted the latest tar file, take a look at
  the README and INSTALL files for installation hints.  In particular,
  be sure to adjust the variables in Makefile and in include/config.h to
  match your environment.  Normally, you won't need to change anything
  when building under Linux, but it is always a good idea to double
  check.  If you're satisfied with the configuration, simply type make
  to build it (if you're not building under Linux, be advised that aboot
  requires GNU make).

  After running make, the aboot directory should contain the following
  files:


     aboot
        This is the actual aboot executable (either an ECOFF or ELF
        object file).

     bootlx
        Same as above, but it contains only the text, data and bss
        segments---that is, this file is not an object file.

     sdisklabel/writeboot
        Utility to install aboot on a hard disk.

     tools/e2writeboot
        Utility to install aboot on an ext2 filesystem (usually used for
        floppies only).

     tools/isomarkboot
        Utility to install aboot on a iso9660 filesystem (used by CD-ROM
        distributors).

     tools/abootconf
        Utility to configure an installed aboot.


  3.2.  Floppy Installation

  The bootloader can be installed on a floppy using the e2writeboot
  command (note: this can't be done on a Jensen since its firmware does
  not support booting from floppy).  This command requires that the disk
  is not overly fragmented as it needs to find enough contiguous file
  blocks to store the entire aboot image (currently about 90KB).  If
  e2writeboot fails because of this, reformat the floppy and try again
  (e.g., with fdformat(1)).  For example, the following steps install
  aboot on floppy disk assuming the floppy is in drive /dev/fd0:






  fdformat /dev/fd0
  mke2fs /dev/fd0
  e2writeboot /dev/fd0 bootlx






  3.3.  Harddisk Installation

  Since the e2writeboot command may fail on highly fragmented disks and
  since reformatting a harddisk is not without pain, it is generally
  safer to install aboot on a harddisk using the swriteboot command.
  swriteboot requires that the first few sectors are reserved for
  booting purposes.  We suggest that the disk be partitioned such that
  the first partition starts at an offset of 2048 sectors.  This leaves
  1MB of space for storing aboot.  On a properly partitioned disk, it is
  then possible to install aboot as follows (assuming the disk is
  /dev/sda):



       swriteboot /dev/sda bootlx





  On systems where partition c in the entire disk it will be neccesary
  to 'force' the write of aboot. In this case use the -f flag followed
  by the partition number (in the case of parition c this is 3).



       swriteboot /dev/sda bootlx -f3





  On a Jensen, you will want to leave some more space, since you need to
  write a kernel to this place, too---2MB should be sufficient when
  using compressed kernels.  Use swriteboot as described in Section ``''
  to write bootlx together with the Linux kernel.


  3.4.  CD-ROM Installation

  To make a CD-ROM bootable by SRM, simply build aboot as described
  above.  Then, make sure that the bootlx file is present on the iso9660
  filesystem (e.g., copy bootlx to the directory that is the filesystem
  master, then run mkisofs on that directory).  After that, all that
  remains to be done is to mark the filesystem as SRM bootable.  This is
  achieved with a command of the form:



       isomarkboot filesystem bootlx




  The command above assumes that filesystem is a file containing the
  iso9660 filesystem and that bootlx has been copied into the root
  directory of that filesystem.  That's it!
  3.5.  Building the Linux Kernel

  A bootable Linux kernel can be built with the following steps.  During
  the make config, be sure to answer "yes" to the question whether you
  want to boot the kernel via SRM (for certain platforms this is
  automatically selected).



       cd /usr/src/linux
       make config
       make dep
       make boot
       make modules (if applicable)
       make modules_install (if applicable)





  The last command will build the file arch/alpha/boot/vmlinux.gz which
  can then be copied to the disk from which you want to boot from.  In
  our floppy disk example above, this would entail:



       mount /dev/fd0 /mnt
       cp arch/alpha/boot/vmlinux.gz /mnt
       umount /mnt






  3.6.  Booting Linux

  With the SRM firmware and aboot installed, Linux is generally booted
  with a command of the form:


       boot devicename -fi filename -fl flags



  The filename and flags arguments are optional.  If they are not
  specified, SRM uses the default values stored in environment variables
  BOOTDEF_DEV ,  BOOT_OSFILE and BOOT_OSFLAGS.  The syntax and meaning
  of these two arguments is described in more detail below. To list the
  current values of these variables type show boot* at the SRM command
  prompt. This will also show a boot_dev variable (among others), this
  variable is read only and needs to be changed via the bootdef_dev
  variable.


  3.6.1.  Device Naming

  This corresponds to the device from which SRM will attempt to boot.
  Examples include:

  dva0   -First floppy drive, /dev/fd0 under Linux

  dqa0   -Primary IDE cdrom as Master, /dev/hda under Linux

  dqa1   -Primary IDE cdrom as Slave, /dev/hdb under Linux

  dqa0*  -Primary IDE hard disk as Master, first partition, /dev/hda1
  under Linux

  dqa1*  -Primary IDE hard disk as Slave, third partition, /dev/hdb3
  under Linux

  dka0*  -SCSI disk on first bus, Device 0 partition 2, /dev/sda2 under
  Linux

  ewa0** -First Ethernet Device, /dev/eth0 under Linux


  * - partition numbers are given as a prefix to the filename when
  booting via SRM, for example 2/boot/vmlinux.gz

  ** - SRM console can network boot via recognized Ethernet devices.


  For example to boot from the disk at SCSI id 6, you would enter:

  boot dka600


  To list the devices currently installed in the system type show dev at
  the SRM command line.


  3.6.2.  Boot Filename

  The filename argument takes the form:

       [n/]filename


  n is a single digit in the range 1..8 that gives the partition number
  from which to boot from.  filename is the path of the file you want
  boot.  For example to boot a kernel named vmlinux.gz from the second
  partition of SCSI device 6, you would enter:



       boot dka600 -file 2/vmlinux.gz




  Or to boot from floppy drive 0, you'd enter:



       boot dva0 -file vmlinux.gz





  If a disk has no partition table , aboot pretends the disk contains
  one ext2 partition starting at the first diskblock.  This allows
  booting from floppy disks.


  As a special case, partition number 0 is used to request booting from
  a disk that does not (yet) contain a file system.  When specifying
  "partition" number 0, aboot assumes that the Linux kernel is stored
  right behind the aboot image.  Such a layout can be achieved with the
  swriteboot command.  For example, to setup a filesystem-less boot from
  /dev/sda, one could use the command:



       swriteboot /dev/sda bootlx vmlinux.gz





  Booting a system in this way is not normally necessary.  The reason
  this feature exists is to make it possible to get Linux installed on a
  systems that can't boot from a floppy disk (e.g., the Jensen).



  3.6.3.  Boot Flags

  A number of bootflags can be specified.  The syntax is:


       -flags "options..."




  Where "options..." is any combination the following options (separated
  by blanks).  There are many more bootoptions, depending on what
  drivers your kernel has installed.  The options listed below are
  therefore just examples to illustrate the general idea:



     load_ramdisk=1
        Copy root file system from a (floppy) disk to the RAM disk
        before starting the system.  The RAM disk will be used in lieu
        of the root device.  This is useful to bootstrap Linux on a
        system with only one floppy drive.


     floppy=str
        Sets floppy configuration to str.


     root=dev
        Select device dev as the root-file system. The device can be
        specified as a major/minor hex number (e.g., 0x802 for
        /dev/sda2) or one of a few canonical names (e.g., /dev/fd0,
        /dev/sda2).


     single
        Boot system in single user mode.


     kgdb
        Enable kernel-gdb (works only if CONFIG_KGDB is enabled; a
        second Alpha system needs to be connected over the serial port
        in order to make this work)



  Some SRM implementations (e.g., the one for the Jensen) are
  handicapped and allow only short option strings (e.g., at most 8
  characters).  In such a case, aboot can be booted with the single-
  character boot flag "i".  With this flag, aboot will prompt the user
  to interacively enter a boot option string of up to 256 characters.
  For example:



       boot dka0 -fl i
       aboot> 3/vmlinux.gz root=/dev/sda3 single




  Since booting in that manner quickly becomes tedious, aboot allows to
  define short-hands for frequently used commandlines.  In particular, a
  single digit option (0-9) requests that aboot uses the corresponding
  option string stored in file /etc/aboot.conf.  A sample aboot.conf is
  shown below:



       #
       # aboot default configurations
       #
       0:3/vmlinux.gz root=/dev/sda3
       1:3/vmlinux.gz root=/dev/sda3 single
       2:3/vmlinux.new.gz root=/dev/sda3
       3:3/vmlinux root=/dev/sda3
       8:- root=/dev/sda3            # fs-less boot of raw kernel
       9:0/vmlinux.gz root=/dev/sda3 # fs-less boot of (compressed) ECOFF kernel
       -




  With this configuration file, the command



       boot dka0 -fl 1




  corresponds exactly to the boot command shown above.  It is quite easy
  to forget what number corresponds to what option string.  To alleviate
  this problem, boot with option "h" and aboot will print the contents
  of /etc/aboot.conf before issuing the prompt for the full option
  string.

  Finally, whenever aboot prompts for an option string, it is possible
  to enter one of the single character flags ("i", "h", or "0"-"9") to
  get the same effect as if that flag had been specified in the boot
  command line.  For example, you could boot with flag "i" and then type
  "h" (followed by return) to remind yourself of the contents of
  /etc/aboot.conf


  3.6.3.1.  Selecting the Partition of /etc/aboot.conf

  When installed on a harddisk, aboot needs to know what partition to
  search for the /etc/aboot.conf file.  A newly compiled aboot will
  search the second partition (e.g., /dev/sda2).  Since it would be
  inconvenient to have to recompile aboot just to change the partition
  number, abootconf allows to directly modify an installed aboot.
  Specifically, if you want to change aboot to use the third partition
  on disk /dev/sda, you'd use the command:

       abootconf /dev/sda 3




  You can verify the current setting by simply omitting the partition
  number.  That is: abootconf /dev/sda will print the currently selected
  partition number.  Note that aboot does have to be installed already
  for this command to succeed.  Also, when installing a new aboot, the
  partition number will fall back to the default (i.e., it will be
  necessary to rerun abootconf).

  Since aboot version 0.5, it is also possible to select the aboot.conf
  partition via the boot command line. This can be done with a command
  line of the form a:b where a is the partition that holds
  /etc/aboot.conf and b is a single-letter option as described above
  (0-9, i, or h). For example, if you type boot -fl "3:h" dka100 the
  system boots from SCSI ID 1, loads /etc/aboot.conf from the third
  partition, prints its contents on the screen and waits for you to
  enter the boot options.


  3.7.  Installation Linux Distributions

  3.7.1.  Installation from the Red Hat 6.0 CD

  Red Hat have made their distribution CD bootable from SRM console *.
  To start an installation, put the CD in and type the following:

  boot srm-device -file kernels/generic.gz -flags root=linux-device

  In the above, the SRM device name and Linux device name for your CD-
  ROM drive are needed.  For Example if the machine had an IDE cdrom
  installed as primary master the command would look like this:


  boot dqa0 -file kernels/generic.gz -flags "root=/dev/hda"


  See the section on ``'' conventions if you don't know what these are.

  * - Please note that through the official RedHat CD-ROM is SRM
  bootable, copies made by various other companies may not be bootable.


  3.7.2.  Installation from the SuSE 6.1 CD

  The SuSE 6.1 CD is not bootable from SRM console. SuSE have an
  alternative approach which involves creating two boot floppies, the
  images of which are included on the CD.  The boot disks can be created
  in various ways, depending on the systems you have available


  Writing the boot disks from a linux system The command to use is dd.
  From the mount-point of SuSE CD 1, the commands are:

  dd if=disks/aboot of=/dev/fd0

  dd if=disks/install of=/dev/fd0


  Writing the boot disks from a windows system The command to use is
  rawrite. It is available on the CD.

  rawrite

  The program then prompts for input disk image and output disk drive.
  Run this command once for each of the disk images as shown above.


  Starting the SuSE installer from the boot disks With the floppy disk
  made from the aboot image in place, type:

  boot dva0 -file vmlinux.gz -flags "root=/dev/fd0 load_ramdisk=1"

  This will start the kernel, prompt you for the second boot disk, and
  start the installer


  3.8.  Booting Over the Network

  Two preliminary steps are necessary before Linux can be booted via a
  network.  First, you need to set the SRM environment variables to
  enable booting via the bootp protocol and second you need to setup
  another machine as the your boot server.  Please refer to the SRM
  documentation that came with your machine for information on how to
  enable bootp.  Setting up the boot server is obviously dependent on
  what operating system that machine is running, but typically it
  involves starting the program bootpd in the background after
  configuring the /etc/bootptab file.  The bootptab file has one entry
  describing each client that is allowed to boot from the server.  For
  example, if you want to boot the machine myhost.cs.arizona.edu, then
  an entry of the following form would be needed:



       myhost.cs.arizona.edu:\
               :hd=/remote/:bf=vmlinux.bootp:\
               :ht=ethernet:ha=08012B1C51F8:hn:vm=rfc1048:\
               :ip=192.12.69.254:bs=auto:




  This entry assumes that the machine's Ethernet address is 08012B1C51F8
  and that its IP address is 192.12.69.254.  The Ethernet address can be
  found with the show device command of the SRM console or, if Linux is
  running, with the ifconfig command.  The entry also defines that if
  the client does not specify otherwise, the file that will be booted is
  vmlinux.bootp in directory /remote.  For more information on
  configuring bootpd, please refer to its man page.

  Next, build aboot with with the command make netboot.  Make sure the
  kernel that you want to boot has been built already.  By default, the
  aboot Makefile uses the kernel in
  /usr/src/linux/arch/alpha/boot/vmlinux.gz (edit the Makefile if you
  want to use a different path).  The result of make netboot is a file
  called vmlinux.bootp which contains aboot and the Linux kernel, ready
  for network booting.

  Finally, copy vmlinux.bootp to the bootsever's directory.  In the
  example above, you'd copy it into /remote/vmlinux.bootp.  Next, power
  up the client machine and boot it, specifying the Ethernet adapter as
  the boot device.  Typically, SRM calls the first Ethernet adapter
  ewa0, so to boot from that device, you'd use the command:



       boot ewa0



  The -fi and -fl options can be used as usual.  In particular, you can
  ask aboot to prompt for Linux kernel arguments by specifying the
  option -fl i.


  3.9.  Partitioning Disks

  3.9.1.  What is a disklabel?

  A disk label is a partition table. Unfortunately, there are several
  formats the partition table can take, depending on the operating
  system.


  DOS partition tables are the standard used by Linux and Windows.
  AlphaBIOS systems and every Linux kernel can read DOS partition
  tables. Unfortunately, SRM console can't.

  BSD disklabels are used by several variants of Unix, including Tru64.
  SRM console can read BSD disklabels, and so can Linux kernels (with
  BSD disklabel support built in). To make        the partitions of a
  disk visible to SRM console, a BSD disklabel is needed.


  To boot from a disk using SRM, a BSD disklabel is required. If the
  disk is not a boot disk, the BSD disklabel is not required. A BSD
  disklabel can be created using fdisk, the standard Linux disk
  partitioning tool.


  3.9.2.  Partitioning the Easy Way: a DOS Disklabel

  The simplest way to partition your disk is to let your Linux installer
  do it for you, for example by using Red Hat's disk druid or fdisk.
  This will produce a DOS disklabel.  It will be readable by Linux, but
  you will not be able to boot from it via SRM.


  3.9.3.  Partitioning with a BSD Disklabel


  1. Start fdisk on the disk you're configuring

  2. Choose to make a BSD disklabel - option 'b'

  3. You'll notice some things: Partitions are letters instead of
     numbers, from a-h Partition 'c' covers the whole of the disk. This
     is the convention, don't touch it.  While you can see it, note down
     the disk parameters as you'll use them more often than with the
     DOS-disklabel approach

  4. Creating a new partition uses the same procedure as the DOS-
     disklabel approach, except that the partitions are referred to by
     letter instead of number. That is, followed by the partition letter
     followed by the starting block followed by the end block

  5. Setting partition type is slightly different, because the numbering
     scheme is different (1 is swap, 8 is ext2).

  6. When you are finished, write ('w') and quit ('q') as normal.

  There are some important catches that you must be aware of when
  partitioning using a BSD disklabel

  o  Partition 'a' should start about 2M into the disk: don't start it
     at sector 1, try starting at sector 10 (for example). This leaves
     plenty of space for writing the boot block (see below)

  o  There is a bug in some versions of fdisk which makes the disk look
     one sector bigger than it actually is.  The listing when you create
     the BSD disklabel is correct.  The last sector of partition 'c' is
     correct.  The default last sector when creating a new partition is
     1 sector too big

  o  Always adjust for this extra sector. This bug exists in the version
     of fdisk shipped with Red Hat 6.0. Not making an adjustment for
     this problem almost always leads to "Access beyond end of device"
     errors from the Linux kernel.

  Once you have made a BSD disklabel, continue the installation. After
  installation, you can write a boot block to your disk to make it
  bootable from SRM.



  4.  Sharing a Disk With DEC Unix

  Unfortunately, DEC Unix doesn't know anything about Linux, so sharing
  a single disk between the two OSes is not entirely trivial.  However,
  it is not a difficult task if you heed the tips in this section.  The
  section assumes you are using aboot version 0.5 or newer.


  4.1.  Partitioning the disk

  First and foremost: never use any of the Linux partitioning programs
  (minlabel or fdisk) on a disk that is also used by DEC Unix.  The
  Linux minlabel program uses the same partition table format as DEC
  Unix disklabel, but there are some incompatibilities in the data that
  minlabel fills in, so DEC Unix will simply refuse to accept a
  partition table generated by minlabel.  To setup a Linux ext2
  partition under DEC Unix, you'll have to change the disktab entry for
  your disk.  For the purpose of this discussion, let's assume that you
  have an rz26 disk (a common 1GB drive) on which you want to install
  Linux.  The disktab entry under DEC Unix v3.2 looks like this (see
  file /etc/disktab):



       rz26|RZ26|DEC RZ26 Winchester:\
               :ty=winchester:dt=SCSI:ns#57:nt#14:nc#2570:\
               :oa#0:pa#131072:ba#8192:fa#1024:\
               :ob#131072:pb#262144:bb#8192:fb#1024:\
               :oc#0:pc#2050860:bc#8192:fc#1024:\
               :od#393216:pd#552548:bd#8192:fd#1024:\
               :oe#945764:pe#552548:be#8192:fe#1024:\
               :of#1498312:pf#552548:bf#8192:ff#1024:\
               :og#393216:pg#819200:bg#8192:fg#1024:\
               :oh#1212416:ph#838444:bh#8192:fh#1024:




  The interesting fields here are o?, and p?, where ? is a letter in the
  range a-h (first through 8-th partition).  The o value gives the
  starting offset of the partition (in sectors) and the p value gives
  the size of the partition (also in sectors).  See disktab(4) for more
  info.  Note that DEC Unix likes to define overlapping partitions.  For
  the entry above, the partition layout looks like this (you can verify
  this by adding up the various o and p values):


         a     b         d           e           f
       |---|-------|-----------|-----------|-----------|

                               c
       |-----------------------------------------------|

                            g                 h
                   |-----------------|-----------------|




  DEC Unix insists that partition a starts at offset 0 and that
  partition c spans the entire disk.  Other than that, you can setup the
  partition table any way you like.

  Let's suppose you have DEC Unix using partition g and want to install
  Linux on partition h with partition b being a (largish) swap
  partition.  To get this layout without destroying the existing DEC
  Unix partition, you need to set the partition types explicitly.  You
  can do this by adding a t field for each partition.  In our case, we
  add the following line to the above disktab entry.



               :ta=unused:tb=swap:tg=4.2BSD:th=resrvd8:




  Now why do we mark partition h as "reservd8" instead of "ext2"?  Well,
  DEC Unix doesn't know about Linux.  It so happens that partition type
  "ext2" corresponds to a numeric value of 8, and DEC Unix uses the
  string "reservd8" for that value.  Thus, in DEC Unix speak, "reservd8"
  means "ext2".  OK, this was the hard part.  Now we just need to
  install the updated disktab entry on the disk.  Let's assume the disk
  has SCSI id 5.  In this case, we'd do:



       disklabel -rw /dev/rrz5c rz26




  You can verify that everything is all right by reading back the
  disklabel with disklabel -r /dev/rrz5c.  At this point, you may want
  to reboot DEC Unix and make sure the existing DEC Unix partition is
  still alive and well.  If that is the case, you can shut down the
  machine and start with the Linux installation.  Be sure to skip the
  disk partitioning step during the install.  Since we already installed
  a good partition table, you should be able to proceed and select the
  8th partition as the Linux root partition and the 2nd partition as the
  swap partition.  If the disk is, say, the second SCSI disk in the
  machine, then the device name for these partitions would be /dev/sdb8
  and /dev/sdb2, respectively (note that Linux uses letters to name the
  drives and numbers to name the partitions, which is exactly reversed
  from what DEC Unix does; the Linux scheme makes more sense, of course
  ;-).



  4.2.  Installing aboot

  First big caveat: with the SRM firmware, you can boot one and only one
  operating system per disk.  For this reason, it is generally best to
  have at least two SCSI disks in a machine that you want to dualboot
  between Linux and DEC Unix.  Of course, you could also boot Linux from
  a floppy if speed doesn't matter or over the network, if you have a
  bootp-capable server.  But in this section we assume you want to boot
  Linux from a disk that contains one or more DEC Unix partitions.

  Second big caveat: installing aboot on a disk shared with DEC Unix
  renders the first and third partition unusable (since those must have
  a starting offset of 0).  For this reason, we recommend that you
  change the size of partition a to something that is just big enough to
  hold aboot (1MB should be plenty).

  Once these two caveats are taken care of, installing aboot is almost
  as easy as usual: since partition a and c will overlap with aboot, we
  need to tell swriteboot that this is indeed OK.  We can do this under
  Linux with a command line of the following form (again, assuming we're
  trying to install aboot on the second SCSI disk):



       swriteboot -f1 -f3 /dev/sdb bootlx




  The -f1 means that we want to force writing bootlx even though it
  overlaps with partition 1.  The corresponding applies for partition 3.

  This is it.  You should now be able to shutdown the system and boot
  Linux from the harddisk.  In our example, the SRM command line to do
  this would be:



       boot dka5 -fi 8/vmlinux.gz -fl root=/dev/sdb8





  5.  Document History

  v0.5.2 5 December 1999 Added comments and information from Stig Telfer
  (stig @ alpha-processor.com).

  o  Added chart on SRM to Linux name mappings

  o  Added RedHat 6.0 and SuSE 6.1 installation information

  o  Added Disk Partitioning Information


  v0.5.1 (Not Released) 13 November 1999 Took the original 0.5 document
  and updated several parts:


  o  Update information on SRM booting from IDE devices

  o  Fixed URL to aboot source

  o  Update toc page to reflect MILO's future

  o  Included information on bootdef_dev and boot_dev to chapter 3

  o  Added this section

  v0.5 17 August 1996 - Original Document by David Mosberger-Tang

































































