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  Linux BootPrompt-Howto
  Paul Gortmaker, Editor.
  v1.01, 18 August 1995

  This is the BootPrompt-Howto, which is a compilation of all the possi¡
  ble boot time arguments that can be passed to the Linux kernel at boot
  time. This includes all kernel and device parameters.  An overview of
  some of the popular software used to boot Linux kernels is included.

  1.  Introduction

  The kernel has a limited capability to accept information at boot in
  the form of a `command line', similar to an argument list you would
  give to a program. In general this is used to supply the kernel with
  information about hardware parameters that the kernel would not be
  able to determine on its own, or to avoid/override the values that the
  kernel would otherwise detect.

  However, if you just copy a kernel image directly to a floppy, (e.g.
  cp zImage /dev/fd0) then you are not given a chance to specify any
  arguments to that kernel. So most Linux users will use software like
  LILO or loadlin that takes care of handing these arguments to the
  kernel, and then booting it.

  This present revision covers distribution kernels up to and including
  v1.2.13. Information pertaining to development kernels up to version
  1.3.18 is also documented.

  The BootPrompt-Howto is edited and maintained by:

       Paul Gortmaker, [e-mail]

  1.1.  Disclaimer and Copyright

  This document is not gospel. However, it is probably the most up to
  date info that you will be able to find. Nobody is responsible for
  what happens to your hardware but yourself. If your hardware goes up
  in smoke (...nearly impossible!)  I take no responsibility. ie. THE
  AUTHOR IS NOT RESPONSIBLE FOR ANY DAMAGES INCURRED DUE TO ACTIONS
  TAKEN BASED ON THE INFORMATION INCLUDED IN THIS DOCUMENT.

  This document is Copyright (c) 1995 by Paul Gortmaker. Permission is
  granted to make and distribute verbatim copies of this manual provided
  the copyright notice and this permission notice are preserved on all
  copies.

  Permission is granted to copy and distribute modified versions of this
  document under the conditions for verbatim copying, provided that this
  copyright notice is included exactly as in the original, and that the
  entire resulting derived work is distributed under the terms of a
  permission notice identical to this one.

  Permission is granted to copy and distribute translations of this
  document into another language, under the above conditions for
  modified versions.

  If you are intending to incorporate this document into a published
  work, please contact me, and I will make an effort to ensure that you
  have the most up to date information available. In the past, out of
  date versions of the Linux howto documents have been published, which
  caused the developers undue grief from being plagued with questions
  that were already answered in the up to date versions.

  1.2.  Related Documentation

  The most up-to-date documentation will always be the kernel source
  itself. Hold on! Don't get scared. You don't need to know any
  programming to read the comments in the source files.  For example, if
  you were looking for what arguments could be passed to the AHA1542
  SCSI driver, then you would go to the linux/drivers/scsi directory,
  and look at the file aha1542.c -- and within the first 100 lines, you
  would find a plain english description of the boot time arguments that
  the 1542 driver accepts.

  If you have figured out what boot-args you intend to use, and now want
  to know how to get that information to the kernel, then look at the
  documentation that comes with the software that you use to boot the
  kernel (e.g. LILO or loadlin).

  1.3.  The Linux Newsgroups

  If you have questions about passing boot arguments to the kernel,
  please READ this document first. If this and the related documentation
  mentioned above does not answer your question(s) then you can try the
  Linux newsgroups.

  General questions on how to configure your system should be directed
  to comp.os.linux.setup.  We ask that you please respect this general
  guideline for content, and don't cross-post your request to other
  groups.

  1.4.  New Versions of this Document

  New versions of this document can be retrieved via anonymous FTP from
  sunsite.unc.edu, in /pub/Linux/docs/HOWTO/* and various Linux ftp
  mirror sites. Updates will be made as new information / drivers
  becomes available. If this copy that you are reading is more than 3
  months old, it is either out of date, or it means that I have been
  lazy and haven't updated it.  This document was produced by using the
  SGML system that was specifically set up for the Linux Howto project,
  and there are various output formats available, including, postscript,
  dvi, ascii, html, and soon TeXinfo.

  I would recommend viewing it in the html (via a WWW browser) or the
  Postscript/dvi format. Both of these contain cross-references that are
  lost in the ascii translation.

  If you want to get the official copy off sunsite, here is URL.

  BootPrompt-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/BootPrompt-
  HOWTO.html>

  If minor additions and changes have been made, you can view the latest
  working copy from this URL.

  Working Copy <http://rsphy1.anu.edu.au/~gpg109/BootPrompt-HOWTO.html>

  2.  Overview of Boot Prompt Arguments

  This section gives some examples of software that can be used to pass
  kernel boot-time arguments to the kernel itself.  It also gives you an
  idea of how the arguments are processed, what limitations there are on
  the boot args, and how they filter down to each appropriate device
  that they are intended for.

  2.1.  LILO (LInux LOader)

  The LILO program (LInux LOader) written by Werner Almesberger is the
  most commonly used. It has the ability to boot various kernels, and
  stores the configuration information in a plain text file. Most
  distributions ship with LILO as the default boot-loader. LILO can boot
  DOS, OS/2 Linux, FreeBSD, etc. without any difficulties, and is quite
  flexible.

  LILO ships with excellent documentation, and for the purposes of boot
  args discussed here, the LILO append= command is of significant
  importance.

  2.2.  LoadLin

  The other commonly used Linux loader is `LoadLin' which is a DOS
  program that has the capability to launch a Linux kernel from the DOS
  prompt (with boot-args) assuming that certain resources are available.
  This is good for people that use DOS and want to launch into Linux
  from DOS.

  It is also very useful if you have certain hardware which relies on
  the supplied DOS driver to put the hardware into a known state. A
  common example is `SoundBlaster Compatible' sound cards that require
  the DOS driver to twiddle a few mystical registers to put the card
  into a SB compatible mode. Booting DOS with the supplied driver, and
  then loading Linux from the DOS prompt with loadlin avoids the reset
  of the card that happens if one rebooted instead. Thus the card is
  left in a Sb compatible mode and hence is useable under Linux.

  There are also other programs that can be used to boot Linux.  For a
  complete list, please look at the programs available on your local
  Linux ftp mirror, under system/Linux-boot/.

  2.3.  The ``rdev'' utility

  There are a few of the kernel boot parameters that have their default
  values stored in various bytes in the kernel image itself.  There is a
  utility called rdev that is installed on most systems that knows where
  these values are, and how to change them.  It can also change things
  that have no kernel boot argument equivalent, such as the default
  video mode used.

  The rdev utility is usually also aliased to swapdev, ramsize, vidmode
  and rootflags. These are the five things that rdev can change, those
  being the root device, the swap device, the RAM disk size, the default
  video mode, and the readonly/readwrite setting of root device.

  More information on rdev can be found by typing rdev -h or by reading
  the supplied man page.

  2.4.  How the Kernel Sorts the Arguments

  Most of the boot args take the form of:

  ______________________________________________________________________
          name[=value_1][,value_2]...[,value_11]
  ______________________________________________________________________

  where `name' is a unique keyword that is used to identify what part of
  the kernel the associated values (if any) are to be given to. Multiple
  boot args are just a space separated list of the above format. Note
  the limit of 11 is real, as the present code only handles 11 comma
  separated parameters per keyword. (However, you can re-use the same
  keyword with up to an additional 11 parameters in unusually
  complicated situations, assuming the setup function supports it.)

  Most of the sorting goes on in linux/init/main.c.  First, the kernel
  ckecks to see if the argument is any of the special arguments `root=',
  `ro', `rw', or `debug'.  The meaning of these special arguments is
  described further on in the document.

  Then it walks a list of setup functions (contained in the bootsetups
  array) to see if the specified argument string (such as `foo') has
  been associated with a setup function (`foo_setup()') for a particular
  device or part of the kernel. If you passed the kernel the line
  foo=3,4,5,6 then the kernel would search the bootsetups array to see
  if `foo' was registered. If it was, then it would call the setup
  function associated with `foo' (foo_setup()) and hand it the arguments
  3, 4, 5 and 6 as given on the kernel command line.

  2.5.  Setting Environment Variables.

  Anything of the form `foo=bar' that is not accepted as a setup funtion
  as described above is then interpreted as an environment variable to
  be set. A (useless?) example would be to use `TERM=vt100' as a boot
  argument.

  2.6.  Passing Arguments to `init'

  Any remaining arguments that were not picked up by the kernel and were
  not interpreted as environment variables are then passed onto process
  one, which is usually the init program. The most common argument that
  is passed to the init process is the word single which instructs init
  to boot the computer in single user mode, and not launch all the usual
  daemons. Check the manual page for the version of init installed on
  your system to see what arguments it accepts.

  3.  General Non-Device Specific Boot Args

  These are the boot arguments that are not related to any specific
  device or peripheral. They are instead related to certain internal
  kernel parameters.

  3.1.  The `no387' Argument

  Some i387 coprocessor chips have bugs that show up when used in 32 bit
  protected mode. For example, some of the early ULSI-387 chips would
  cause solid lockups while performing floating point calculations.
  Using the `no387' boot arg causes Linux to ignore the maths
  coprocessor even if you have one. Of course you must then have your
  kernel compiled with math emulation support!

  3.2.  The `no-hlt' Argument

  The i386 (and sucessors thereof) family of CPUs have a `hlt'
  instruction which tells the CPU that nothing is going to happen until
  an external device (keyboard, modem, disk, etc.) calls upon the CPU to
  do a task. This allows the CPU to enter a `low-power' mode where it
  sits like a zombie until an external device wakes it up (usually via
  an interrupt).  Some of the early i486DX-100 chips had a problem  with
  the `hlt' instruction, in that they couldn't reliably return to
  operating mode after this instruction was used. Using the `no-hlt'
  instruction tells Linux to just run an infinite loop when there is
  nothing else to do, and to not halt your CPU when there is no
  activity. This allows people with these broken chips to use Linux,
  although they would be well advised to seek a replacement through a
  warranty where possible.

  3.3.  The `root=' Argument

  This argument tells the kernel what device is to be used as the root
  filesystem while booting. The default of this setting is the value of
  the root device of the system that the kernel was built on.  For
  example, if the kernel in question was built on a system that used
  `/dev/hda1' as the root partition, then the default root device would
  be `/dev/hda1'.  To override this default value, and select the second
  floppy drive as the root device, one would use `root=/dev/fd1'.

  Valid root devices are partitions on any of the following disk
  devices:

  (1) /dev/hdaN to /dev/hddN, which is partition N on ST-506 compatible
  disk `a to d'.

  (2) /dev/sdaN to /dev/sdeN, which is partition N on SCSI compatible
  disk `a to e'.

  (3) /dev/xdaN to /dev/xdbN, which is partition N on XT compatible disk
  `a to b'.

  (4) /dev/fdN, which is floppy disk drive number N. Having N=0 would be
  the DOS `A:' drive, and N=1 would be `B:'.

  The more awkward and less portable numeric specification of the above
  possible root devices in major/minor format is also accepted. (e.g.
  /dev/sda3 is major 8, minor 3, so you could use root=0x803 as an
  alternative.)

  This is one of the few kernel boot arguments that has its default
  stored in the kernel image, and which can thus be altered with the
  rdev utility.

  3.4.  The `ro' Argument

  When the kernel boots, it needs a root filesystem to read basic things
  off of. This is the root filesystem that is mounted at boot. However,
  if the root filesystem is mounted with write access, you can not
  reliably check the filesystem integrity with half-written files in
  progress. The `ro' option tells the kernel to mount the root
  filesystem as `readonly' so that any filesystem consistency check
  programs (fsck) can safely assume that there are no half-written files
  in progress while performing the check. No programs or processes can
  write to files on the filesystem in question until it is `remounted'
  as read/write capable.

  This is one of the few kernel boot arguments that has its default
  stored in the kernel image, and which can thus be altered with the
  rdev utility.

  3.5.  The `rw' Argument

  This is the exact opposite of the above, in that it tells the kernel
  to mount the root filesytem as read/write. The default is to mount the
  root filesystem as read/write anyways. Do not run any `fsck' type
  programs on a filesystem that is mounted read/write.

  The same value stored in the image file mentioned above is also used
  for this parameter, accesible via rdev.

  3.6.  The `debug' Argument

  The kernel communicates important (and not-so important) messages to
  the operator via the printk() function.  If the message is considered
  important, the printk() function will put a copy on the present
  console as well as handing it off to the klogd() facility so that it
  gets logged to disk. The reason for printing important messages to the
  console as well as logging them to disk is because under unfortunate
  circumstances (e.g. a disk failure) the message won't make it to disk
  and will be lost.

  The threshold for what is and what isn't considered important is set
  by the console_loglevel variable. The default is to log anything more
  important than DEBUG (level 7) to the console. (These levels are
  defined in the include file kernel.h) Specifying debug as a boot
  argument will set the console loglevel to 10, so that all kernel
  messages appear on the console.

  The console loglevel can usually also be set at run time via an option
  to the klogd() program. Check the man page for the version installed
  on your system to see how to do this.

  3.7.  The `reserve=' Argument

  This is used to protect I/O port regions from probes.  The form of the
  command is:

       reserve=iobase,extent[,iobase,extent]...

  In some machines it may be necessary to prevent device drivers from
  checking for devices (auto-probing) in a specific region. This may be
  because of poorly designed hardware that causes the boot to freeze
  (such as some ethercards), hardware that is mistakenly identified,
  hardware whose state is changed by an earlier probe, or merely
  hardware you don't want the kernel to initialize.

  The reserve boot-time argument addresses this problem by specifying an
  I/O port region that shouldn't be probed. That region is reserved in
  the kernel's port registration table as if a device has already been
  found in that region. Note that this mechanism shouldn't be necessary
  on most machines. Only when there is a problem or special case would
  it be necessary to use this.

  The I/O ports in the specified region are protected against device
  probes. This was put in to be used when some driver was hanging on a
  NE2000, or misidentifying some other device as its own.  A correct
  device driver shouldn't probe a reserved region, unless another boot
  argument explicitly specifies that it do so.  This implies that
  reserve will most often be used with some other boot argument. Hence
  if you specify a reserve region to protect a specific device, you must
  generally specify an explicit probe for that device. Most drivers
  ignore the port registration table if they are given an explicit
  address.

  For example, the boot line

  ______________________________________________________________________
          reserve=0x300,32  blah=0x300
  ______________________________________________________________________

  keeps all device drivers except the driver for `blah' from probing
  0x300-0x31f.

  As usual with boot-time specifiers there is an 11 parameter limit,
  thus you can only specify 5 reserved regions per reserve keyword.
  Multiple reserve specifiers will work if you have an unusually
  complicated request.

  3.8.  The `ramdisk=' Argument

  This specifies the size in kB of the optional RAM disk device.  For
  example, if one wished to have a root filesystem on a 1.44MB floppy
  loaded into the RAM disk device, they would use:

  ______________________________________________________________________
          ramdisk=1440
  ______________________________________________________________________

  This is one of the few kernel boot arguments that has its default
  stored in the kernel image, and which can thus be altered with the
  rdev utility.

  3.9.  The `mem=' Argument

  The original BIOS call defined in the PC specification  that returns
  the amount of installed memory was only designed to be able to report
  up to 64MB. (Yes, another lack of foresight, just like the 1024
  cylinder disks... sigh.) Linux uses this BIOS call at boot to
  determine how much memory is installed.  If you have more than 64MB of
  RAM installed, you can use this boot arg to tell Linux how much memory
  you have.  Here is a quote from Linus on usage of the `mem='
  parameter.

  ``The kernel will accept any `mem=xx' parameter you give it, and if it
  turns out that you lied to it, it will crash horribly sooner or later.
  The parameter indicates the highest addressable RAM address, so
  `mem=0x1000000' means you have 16MB of memory, for example.  For a
  96MB machine this would be `mem=0x6000000'.

  NOTE NOTE NOTE: some machines might use the top of memory for BIOS
  cacheing or whatever, so you might not actually have up to the full
  96MB addressable.  The reverse is also true: some chipsets will map
  the physical memory that is covered by the BIOS area into the area
  just past the top of memory, so the top-of-mem might actually be 96MB
  + 384kB for example.  If you tell linux that it has more memory than
  it actually does have, bad things will happen: maybe not at once, but
  surely eventually.''

  Note that the argument does not have to be in hex, and the suffixes
  `k' and `M' (case insensitive) can be used to specify kilobytes and
  Megabytes, respectively. (A `k' will cause a 10 bit shift on your
  value, and a `M' will cause a 20 bit shift.)  The above warning still
  holds, in that a 96MB machine may work with mem=97920k but fail with
  either mem=98304k or mem=96M.

  4.  Boot Arguments for SCSI Peripherals.

  This section contains the descriptions of the boot args that are used
  for passing information about the installed SCSI host adapters, and
  SCSI devices.

  General notation for this section:

  iobase -- the first I/O port that the SCSI host occupies.  These are
  specified in hexidecimal notation, and usually lie in the range from
  0x200 to 0x3ff.

  irq -- the hardware interrupt that the card is configured to use.
  Valid values will be dependant on the card in question, but will
  usually be 5, 7, 9, 10, 11, 12, and 15. The other values are usually
  used for common preipherals like IDE hard disks, floppies, serial
  ports, etc.

  scsi-id -- the ID that the host adapter uses to identify itself on the
  SCSI bus. Only some host adapters allow you to change this value, as
  most have it permanently specified internally. The usual default value
  is seven, but the Seagate and Future Domain TMC-950 boards use six.

  parity -- whether the SCSI host adapter expects the attached devices
  to supply a parity value with all information exchanges.  Specifying a
  one indicates parity checking is enabled, and a zero disables parity
  checking. Again, not all adapters will support selection of parity
  behaviour as a boot argument.

  4.1.  Maximum Probed LUNs (`max_scsi_luns=')

  Each SCSI device can have a number of `sub-devices' contained within
  itself. The most common example is one of the new SCSI CD-ROMs that
  handle more than one disk at a time.  Each CD is addressed as a
  `Logical Unit Number' (LUN) of that particular device. But most
  devices, such as hard disks, tape drives and such are only one device,
  and will be assigned to LUN zero.

  The problem arises with single LUN devices with bad firmware.  Some
  poorly designed SCSI devices (old and unfortunately new) can not
  handle being probed for LUNs not equal to zero. They will respond by
  locking up, and possibly taking the whole SCSI bus down with them.

  Newer kernels have the configuration option that allows you to set the
  maximum number of probed LUNs. The default is to only probe LUN zero,
  to avoid the problem described above.

  To specify the number of probed LUNs at boot, one enters
  `max_scsi_luns=n' as a boot arg, where n is a number between one and
  eight. To avoid problems as described above, one would use n=1 to
  avoid upsetting such broken devices

  4.2.  Parameters for SCSI Tape drives (`st=')

  Some boot time configuration of the SCSI tape driver can be achieved
  by using the following:

  ______________________________________________________________________
          st=buf_size[,write_threshold[,max_bufs]]
  ______________________________________________________________________

  The fisrt two numbers are specified in units of kB.  The default
  buf_size is 32kB, and the maximum size that can be specified is a
  ridiculous 16384kB.  The write_threshold is the value at which the
  buffer is committed to tape, with a default value of 30kB.  The
  maximum number of buffers varies with the number of drives detected,
  and has a default of two. An example usage would be:

  ______________________________________________________________________
          st=32,30,2
  ______________________________________________________________________

  Full details can be found in the README.st file that is in the scsi
  directory of the kernel source tree.

  4.3.  Adaptec aha151x, aha152x, aic6260, aic6360, SB16-SCSI
  (`aha152x=')

  The aha numbers refer to cards and the aic numbers refer to the actual
  SCSI chip on these type of cards, including the Soundblaster-16 SCSI.

  The probe code for these SCSI hosts looks for an installed BIOS, and
  if none is present, the probe will not find your card. Then you will
  have to use a boot arg of the form:

  ______________________________________________________________________
           aha152x=iobase[,irq[,scsi-id[,reconnect[,parity]]]]
  ______________________________________________________________________

  Note that if the driver was compiled with debugging enabled, a sixth
  value can be specified to set the debug level.

  All the parameters are as described at the top of this section, and
  the reconnect value will allow device disconnect/reconnect if a non-
  zero value is used. An example usage is as follows:

  ______________________________________________________________________
          aha152x=0x340,11,7,1
  ______________________________________________________________________

  Note that the parameters must be specified in order, meaning that if
  you want to specify a parity setting, then you will have to specify an
  iobase, irq, scsi-id and reconnect value as well.

  4.4.  Adaptec aha154x (`aha1542=')

  These are the aha154x series cards. The aha1542 series cards have an
  i82077 floppy controller onboard, while the aha1540 series cards do
  not. These are busmastering cards, and have parameters to set the
  ``fairness'' that is used to share the bus with other devices. The
  boot arg looks like the following.

  ______________________________________________________________________
          aha1542=iobase[,buson,busoff[,dmaspeed]]
  ______________________________________________________________________

  Valid iobase values are usually one of: 0x130, 0x134, 0x230, 0x234,
  0x330, 0x334.  Clone cards may permit other values.

  The buson, busoff values refer to the number of microseconds that the
  card dominates the ISA bus. The defaults are 11us on, and 4us off, so
  that other cards (such as an ISA LANCE Ethernet card) have a chance to
  get access to the ISA bus.

  The dmaspeed value refers to the rate (in MB/s) at which the DMA
  (Direct Memory Access) transfers proceed at. The default is 5MB/s.
  Newer revision cards allow you to select this value as part of the
  soft-configuration, older cards use jumpers. You can use values up to
  10MB/s assuming that your motherboard is capable of handling it.
  Experiment with caution if using values over 5MB/s.

  4.5.  Adaptec aha274x, aha284x, aic7xxx (`aic7xxx=')

  These boards can accept an argument of the form:

  ______________________________________________________________________
          aic7xxx=extended,no_reset
  ______________________________________________________________________

  The extended value, if non-zero, indicates that extended translation
  for large disks is enabled. The no_reset value, if non-zero, tells the
  driver not to reset the SCSI bus when setting up the host adaptor at
  boot.

  4.6.  BusLogic SCSI Hosts (`buslogic=')

  At present, the buslogic driver accepts only one parameter, that being
  the I/O base. It expects that to be one of the following valid values:
  0x130, 0x134, 0x230, 0x234, 0x330, 0x334.

  4.7.  Future Domain TMC-8xx, TMC-950 (`tmc8xx=')

  The probe code for these SCSI hosts looks for an installed BIOS, and
  if none is present, the probe will not find your card. Or, if the
  signature string of your BIOS is not recognised then it will also not
  be found. In either case, you will then have to use a boot arg of the
  form:

  ______________________________________________________________________
          tmc8xx=mem_base,irq
  ______________________________________________________________________

  The mem_base value is the value of the memory mapped I/O region that
  the card uses. This will usually be one of the following values:
  0xc8000, 0xca000, 0xcc000, 0xce000, 0xdc000, 0xde000.

  4.8.  Pro Audio Spectrum (`pas16=')

  The PAS16 uses a NC5380 SCSI chip, and newer models support jumper-
  less configuration. The boot arg is of the form:

  ______________________________________________________________________
          pas16=iobase,irq
  ______________________________________________________________________

  The only difference is that you can specify an IRQ value of 255, which
  will tell the driver to work without using interrupts, albeit at a
  performance loss. The iobase is usually 0x388.

  4.9.  Seagate ST-0x (`st0x=')

  The probe code for these SCSI hosts looks for an installed BIOS, and
  if none is present, the probe will not find your card. Or, if the
  signature string of your BIOS is not recognised then it will also not
  be found. In either case, you will then have to use a boot arg of the
  form:

  ______________________________________________________________________
          st0x=mem_base,irq
  ______________________________________________________________________

  The mem_base value is the value of the memory mapped I/O region that
  the card uses. This will usually be one of the following values:
  0xc8000, 0xca000, 0xcc000, 0xce000, 0xdc000, 0xde000.

  4.10.  Trantor T128 (`t128=')

  These cards are also based on the NCR5380 chip, and accept the
  following options:

  ______________________________________________________________________
          t128=mem_base,irq
  ______________________________________________________________________

  The valid values for mem_base are as follows: 0xcc000, 0xc8000,
  0xdc000, 0xd8000.

  4.11.  Cards that don't Accept Boot Args

  At present, the following SCSI cards do not make use of any boot-time
  parameters. In some cases, you can hard-wire values by directly
  editing the driver itself, if required.

  Always IN2000, Adaptec aha1740, EATA-DMA, EATA-PIO, Future Domain
  16xx, NCR5380 (generic), NCR53c7xx to NCR53c8xx, Qlogic, Ultrastor
  (incl. u?4f), Western Digital wd7000,

  5.  Hard Disks

  This section lists all the boot args associated with standard MFM/RLL,
  ST-506, XT, and IDE disk drive devices.  Note that both the IDE and
  the generic ST-506 HD driver both accept the `hd=' option.

  5.1.  IDE Disk/CD-ROM Driver Parameters

  The IDE driver accepts a number of parameters, which range from disk
  geometry specifications, to support for broken controller chips. Drive
  specific options are specified by using one of:

  `hda=', `hdb=', `hdc=', or `hdd='.

  Non-drive specific options are specified with the prefix `hd='. Note
  that using a drive specific prefix for a non-drive specific option
  will still work, and the option will just be applied as expected.

  Also note that `hd=' can be used to refer to the next unspecified
  drive in the (a, b, c, d) sequence.  For the following discussions,
  the `hd=' option will be cited for brevity. Please consult the file
  README.ide in the linux/drivers/block directory if more information is
  required.

  5.1.1.  The `hd=cyls,heads,sects[,wpcom[,irq]]' options

  These options are used to specify the physical geometry of the disk.
  Only the first three values are required. The cylinder/head/sectors
  values will be those used by fdisk.  The write precompensation value
  is ignored for IDE disks.  The IRQ value specified will be the IRQ
  used for the interface that the drive resides on, and is not really a
  drive specific parameter.

  5.1.2.  The `hd=serialize' option

  The dual IDE interface CMD-640 chip is broken as designed such that
  when drives on the secondary interface are used at the same time as
  drives on the primary interface, it will corrupt your data. Using this
  option tells the driver to make sure that both interfaces are never
  used at the same time. If you only have up to two drives, both on the
  primary interface, then you don't need to use this option.

  5.1.3.  The `hd=dtc2278' option

  This option tells the driver that you have a DTC-2278D IDE interface.
  The driver then tries to do DTC specific operations to enable the
  second interface and to enable faster transfer modes.

  5.1.4.  The `hd=noprobe' option

  If a particular drive (e.g. old IDE drive) has problems that are a
  result of being probed, this option can be used to disable the probe.
  An example usage could be:

  ______________________________________________________________________
          hdb=noprobe hdb=1166,7,17
  ______________________________________________________________________

  which would disable the probe, but still specify the drive geometry so
  that it would be registered as a valid block device, and hence
  useable.

  5.1.5.  The `hd=nowerr' option

  Some drives apparently have the WRERR_STAT bit stuck on permanently.
  This enables a work-around for these broken devices.

  5.1.6.  The `hd=cdrom' option

  This tells the IDE driver that there is an ATAPI compatible CD-ROM
  attached in place of a normal IDE hard disk. In most cases the CD-ROM
  is identified automatically, but if it isn't then this may help.
  5.2.  Standard ST-506 Disk Driver Options (`hd=')

  The standard disk driver can accept geometry arguments for the disks
  similar to the IDE driver. Note however that it only expects three
  values (C/H/S) -- any more or any less and it will silently ignore
  you. Also, it only accepts `hd=' as an argument, i.e. `hda=', `hdb='
  and so on are not valid here. The format is as follows:

  ______________________________________________________________________
          hd=cyls,heads,sects
  ______________________________________________________________________

  If there are two disks installed, the above is repeated with the
  geometry parameters of the second disk.

  5.3.  XT Disk Driver Options (`xd=')

  If you are unfortunate enough to be using one of these old 8 bit cards
  that move data at a whopping 125kB/s then here is the scoop.  The
  probe code for these cards looks for an installed BIOS, and if none is
  present, the probe will not find your card. Or, if the signature
  string of your BIOS is not recognised then it will also not be found.
  In either case, you will then have to use a boot arg of the form:

  ______________________________________________________________________
          xd=type,irq,iobase,dma_chan
  ______________________________________________________________________

  The type value specifies the particular manufacturer of the card, and
  are as follows: 0=generic; 1=DTC; 2,3,4=Western Digital,
  5,6,7=Seagate; 8=OMTI. The only difference between multiple types from
  the same manufacturer is the BIOS string used for detection, which is
  not used if the type is specified.

  The xd_setup() function does no checking on the values, and assumes
  that you entered all four values. Don't disappoint it.  Here is an
  example usage for a WD1002 controller with the BIOS disabled/removed,
  using the `default' XT controller parameters:

  ______________________________________________________________________
          xd=2,5,0x320,3
  ______________________________________________________________________

  6.  CD-ROMs (Non-SCSI/ATAPI/IDE)

  This section lists all the possible boot args pertaining to CD-ROM
  devices. Note that this does not include SCSI or IDE/ATAPI CD-ROMs.
  See the appropriate section(s) for those types of CD-ROMs.

  6.1.  The Aztech Interface (`aztcd=')

  The syntax for this type of card is:

  ______________________________________________________________________
          aztcd=iobase[,magic_number]
  ______________________________________________________________________

  If you set the magic_number to 0x79 then the driver will try and run
  anyway in the event of an unknown firmware version. All other values
  are ignored.

  6.2.  The CDU-31A and CDU-33A Sony Interface (`cdu31a=')

  This CD-ROM interface is found on some of the Pro Audio Spectrum sound
  cards, and other Sony supplied interface cards.  The syntax is as
  follows:

  ______________________________________________________________________
          cdu31a=iobase,[irq[,is_pas_card]]
  ______________________________________________________________________

  Specifying an IRQ value of zero tells the driver that hardware
  interrupts aren't supported (as on some PAS cards). If your card
  supports interrupts, you should use them as it cuts down on the CPU
  usage of the driver.

  The `is_pas_card' should be entered as `PAS' if using a Pro Audio
  Spectrum card, and otherwise it should not be specified at all.

  6.3.  The CDU-535 Sony Interface (`sonycd535=')

  The syntax for this CD-ROM interface is:

  ______________________________________________________________________
          sonycd535=iobase[,irq]
  ______________________________________________________________________

  A zero can be used for the I/O base as a `placeholder' if one wishes
  to specify an IRQ value.

  6.4.  The GoldStar Interface (`gscd=')

  The syntax for this CD-ROM interface is:

  ______________________________________________________________________
          gscd=iobase
  ______________________________________________________________________

  6.5.  The Mitsumi Standard Interface (`mcd=')

  The syntax for this CD-ROM interface is:

  ______________________________________________________________________
          mcd=iobase,[irq[,wait_value]]
  ______________________________________________________________________

  The wait_value is used as an internal timeout value for people who are
  having problems with their drive, and may or may not be implemented
  depending on a compile time DEFINE.

  6.6.  The Mitsumi XA/MultiSession Interface (`mcdx=')

  At present this `experimental' driver has a setup function, but no
  parameters are implemented yet (as of 1.3.15).  This is for the same
  hardware as above, but the driver has extended features.

  6.7.  The Optics Storage Interface (`optcd=')

  The syntax for this type of card is:

  ______________________________________________________________________
          optcd=iobase
  ______________________________________________________________________

  6.8.  The Phillips CM206 Interface (`cm206=')

  The syntax for this type of card is:

  ______________________________________________________________________
          cm206=[iobase][,irq]
  ______________________________________________________________________

  The driver assumes numbers between 3 and 11 are IRQ values, and
  numbers between 0x300 and 0x370 are I/O ports, so you can specify one,
  or both numbers, in any order.  It also accepts `cm206=auto' to enable
  autoprobing.

  6.9.  The Sanyo Interface (`sjcd=')

  The syntax for this type of card is:

  ______________________________________________________________________
          sjcd=iobase[,irq[,dma_channel]]
  ______________________________________________________________________

  6.10.  The SoundBlaster Pro Interface (`sbpcd=')

  The syntax for this type of card is:

  ______________________________________________________________________
          sbpcd=iobase,type
  ______________________________________________________________________

  where type is one of the following (case sensitive) strings:
  `SoundBlaster', `LaserMate', or `SPEA'.  The I/O base is that of the
  CD-ROM interface, and not that of the sound portion of the card.

  7.  Other Hardware Devices

  Any other devices that didn't fit into any of the above categories got
  lumped together here.

  7.1.  Ethernet Devices (`ether=')

  Different drivers make use of different parameters, but they all at
  least share having an IRQ, an I/O port base value, and a name. In its
  most generic form, it looks something like this:

  ______________________________________________________________________
          ether=irq,iobase[,param_1[,param_2,...param_8]]],name
  ______________________________________________________________________

  The first non-numeric argument is taken as the name.  The param_n
  values (if applicable) usually have different meanings for each
  different card/driver.  Typical param_n values are used to specify
  things like shared memory address, interface selection, DMA channel
  and the like.

  The most common use of this parameter is to force probing for a second
  ethercard, as the default is to only probe for one. This can be
  accomplished with a simple:

  ______________________________________________________________________
          ether=0,0,eth1
  ______________________________________________________________________

  Note that the values of zero for the IRQ and I/O base in the above
  example tell the driver(s) to autoprobe.

  Note that the Ethernet-HowTo has complete and extensive documentation
  on using multiple cards and on the card/driver specific implementation
  of the param_n values where used. Interested readers should refer to
  the section in that document on their particular card for more
  complete information.

  7.2.  The Floppy Disk Driver (`floppy=')

  There are many floppy driver options, and they are all listed in
  README.fd in linux/drivers/block. This information is taken directly
  from that file.

  7.2.1.  floppy=mask,allowed_drive_mask

  Sets the bitmask of allowed drives to mask. By default, only units 0
  and 1 of each floppy controller are allowed. This is done because
  certain non-standard hardware (ASUS PCI motherboards) mess up the
  keyboard when accessing units 2 or 3. This option is somewhat
  obsoleted by the cmos option.

  7.2.2.  floppy=all_drives

  Sets the bitmask of allowed drives to all drives. Use this if you have
  more than two drives connected to a floppy controller.

  7.2.3.  floppy=asus_pci

  Sets the bitmask to allow only units 0 and 1. (The default)

  7.2.4.  floppy=daring

  Tells the floppy driver that you have a well behaved floppy
  controller.  This allows more efficient and smoother operation, but
  may fail on certain controllers. This may speed up certain operations.

  7.2.5.  floppy=0,daring

  Tells the floppy driver that your floppy controller should be used
  with caution.

  7.2.6.  floppy=one_fdc

  Tells the floppy driver that you have only floppy controller (default)

  7.2.7.  floppy=two_fdc or floppy=address,two_fdc

  Tells the floppy driver that you have two floppy controllers. The
  second floppy controller is assumed to be at address. If address is
  not given, 0x370 is assumed.

  7.2.8.  floppy=thinkpad

  Tells the floppy driver that you have a Thinkpad. Thinkpads use an
  inverted convention for the disk change line.
  7.2.9.  floppy=0,thinkpad

  Tells the floppy driver that you don't have a Thinkpad.

  7.2.10.  floppy=drive,type,cmos

  Sets the cmos type of drive to type.  Additionally, this drive is
  allowed in the bitmask. This is useful if you have more than two
  floppy drives (only two can be described in the physical cmos), or if
  your BIOS uses non-standard CMOS types.  Setting the CMOS to 0 for the
  first two drives (default) makes the floppy driver read the physical
  cmos for those drives.

  7.2.11.  floppy=unexpected_interrupts

  Print a warning message when an unexpected interrupt is received
  (default behaviour)

  7.2.12.  floppy=no_unexpected_interrupts or floppy=L40SX

  Don't print a message when an unexpected interrupt is received. This
  is needed on IBM L40SX laptops in certain video modes. (There seems to
  be an interaction between video and floppy. The unexpected interrupts
  only affect performance, and can safely be ignored.)

  7.3.  The Sound Driver (`sound=')

  The sound driver can also accept boot args to override the compiled in
  values. This is not recommended, as it is rather complex. It is
  described in the Readme.Linux file, in linux/drivers/sound. It accepts
  a boot arg of the form:

  ______________________________________________________________________
          sound=device1[,device2[,device3...[,device11]]]
  ______________________________________________________________________

  where each deviceN value is of the following format 0xTaaaId and the
  bytes are used as follows:

  T - device type: 1=FM, 2=SB, 3=PAS, 4=GUS, 5=MPU401, 6=SB16,
  7=SB16-MPU401

  aaa - I/O address in hex.

  I - interrupt line in hex (i.e 10=a, 11=b, ...)

  d - DMA channel.

  As you can see it gets pretty messy, and you are better off to compile
  in your own personal values as recommended. Using a boot arg of
  `sound=0' will disable the sound driver entirely.

  7.4.  The Bus Mouse Driver (`bmouse=')

  The busmouse driver only accepts one parameter, that being the
  hardware IRQ value to be used.

  8.  Closing

  If you have found any glaring typos, or outdated info in this
  document, please let me know. It is easy to overlook stuff.

  Thanks,

  Paul Gortmaker, [e-mail]