Freelog Special Edition 1: Linux/CD1.iso/doc/HOWTO/BootPrompt-HOWTO

Text File | 1998-10-14 | 83KB | 1,830 lines

  The Linux BootPrompt-HowTo
  by Paul Gortmaker.
  v1.14, 1 February 1998

  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.  A discussion of
  how the kernel sorts boot time arguments, along with an overview of
  some of the popular software used to boot Linux kernels is also
  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.

  IMPORTANT NOTE TO MODULE USERS: Boot Prompt arguments typically only
  apply to hardware drivers that are compiled directly into the kernel.
  They have no effect on drivers that are loaded as modules. Most
  distributions use modules. If you are unsure, then look at man depmod
  and man modprobe along with the contents of /etc/conf.modules.

  This present revision covers kernels up to and including v2.0.33.
  Some features that are unique to development/testing kernels up to
  v2.1.84 are also documented.

  The BootPrompt-Howto is by:

       Paul Gortmaker, [e-mail]

  [Please note that boot prompt arguments that are specific to the non-
  i386 ports and devices (esp. Atari/Amiga) are not currently
  documented.]

  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) 1995-1998 by Paul Gortmaker.

  This document may be copied according to the conditions of the GNU
  General Public License, version 2, included herein by reference. See
  the file linux/COPYING that comes with the Linux kernel for full
  details.

  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.

  The next best thing will be any documentation files that are
  distributed with the kernel itself. There are now quite a few of
  these, and most of them can be found in the directory
  linux/Documentation and subdirectories from there.  The linux
  directory is usually found in /usr/src/.  Sometimes there will be
  README.foo files that can be found in the related driver directory
  (e.g. linux/drivers/XXX/, where XXX will be scsi, char, or net).

  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). A brief overview is given below, but it
  is no substitute for the documentation that comes with the booting
  software.

  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.  Of course you should try reading the group before
  blindly posting your question, as somebody else may have already asked
  it, or it may even be a Frequently Asked Question (a FAQ).  A quick
  browse of the linux FAQ before posting is a good idea. You should be
  able to find the FAQ somewhere close to where you found this document.

  General questions on how to configure your system should be directed
  to the comp.os.linux.setup newsgroup.  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
  the site sunsite.unc.edu, in the directory /pub/Linux/docs/HOWTO/.
  Note that SunSITE is usually heavily loaded, and you are better
  advised to get the document from one of the Linux ftp mirror sites.
  Updates will be made as new information and/or drivers becomes
  available. If this copy that you are presently reading is more than a
  few months old, then you should probably check to see if a newer copy
  exists.

  This document was produced by using a modified 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>

  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.

  It is important to note that spaces should not be used in a boot
  argument, but only between separate arguments.  A list of values that
  are for a single argument are to be separated with a comma between the
  values, and again without any spaces. See the following examples
  below.

  ______________________________________________________________________
          ether=9,0x300,0xd0000,0xd4000,eth0  root=/dev/hda1            *RIGHT*
          ether = 9, 0x300, 0xd0000, 0xd4000, eth0  root = /dev/hda1    *WRONG*
  ______________________________________________________________________

  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.

  A typical configuration will have LILO stop and print LILO: shortly
  after you turn on your computer. It will then wait for a few seconds
  for any optional input from the user, and failing that it will then
  boot the default system. Typical system labels that people use in the
  LILO configuration files are linux and backup and msdos. If you want
  to type in a boot argument, you type it in here, after typing in the
  system label that you want LILO to boot from, as shown in the example
  below.

  ______________________________________________________________________
          LILO: linux root=/dev/hda1
  ______________________________________________________________________

  LILO comes with excellent documentation, and for the purposes of boot
  args discussed here, the LILO append= command is of significant
  importance when one wants to add a boot time argument as a permanent
  addition to the LILO config file.  You simply add something like
  append = "foo=bar" to the /etc/lilo.conf file. It can either be added
  at the top of the config file, making it apply to all sections, or to
  a single system section by adding it inside an image= section.  Please
  see the LILO documentation for a more complete description.

  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 set a few proprietary 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.EXE 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 parameters, 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 (man rdev).

  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.)
  Also note that the kernel splits the list into a maximum of ten
  integer arguments, and a following string, so you can't really supply
  11 integers unless you convert the 11th arg from a string to an int in
  the driver itself.

  Most of the sorting goes on in linux/init/main.c.  First, the kernel
  checks 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,bar 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 integer
  arguments 3, 4, 5 and 6 as given on the kernel command line, and also
  hand it the string argument bar.

  2.5.  Setting Environment Variables.

  Anything of the form `foo=bar' that is not accepted as a setup
  function 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 the `init' program

  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, such as memory handling, ramdisk handling, root
  file system handling and others.

  3.1.  Root Filesystem options

  The following options all pertain to how the kernel selects and
  handles the root filesystem.

  3.1.1.  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 any of the following 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:'.

  (5) /dev/nfs, which is not really a device, but rather a flag to tell
  the kernel to get the root fs via the network.

  The more awkward and less portable numeric specification of the above
  possible disk 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.

  3.1.2.  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.

  3.1.3.  The `rw' Argument

  This is the exact opposite of the above, in that it tells the kernel
  to mount the root filesystem as read/write. The default is to mount
  the root filesystem as read/write anyway. 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, accessible via rdev.

  3.2.  Options Relating to RAM Disk Management

  The following options all relate to how the kernel handles the RAM
  disk device, which is usually used for bootstrapping machines during
  the install phase, or for machines with modular drivers that need to
  be installed to access the root filesystem.

  3.2.1.  The `ramdisk_start=' Argument

  To allow a kernel image to reside on a floppy disk along with a
  compressed ramdisk image, the `ramdisk_start=<offset>' command was
  added. The kernel can't be included into the compressed ramdisk
  filesystem image, because it needs to be stored starting at block zero
  so that the BIOS can load the bootsector and then the kernel can
  bootstrap itself to get going.

  Note: If you are using an uncompressed ramdisk image, then the kernel
  can be a part of the filesystem image that is being loaded into the
  ramdisk, and the floppy can be booted with LILO, or the two can be
  separate as is done for the compressed images.

  If you are using a two-disk boot/root setup (kernel on disk 1, ramdisk
  image on disk 2) then the ramdisk would start at block zero, and an
  offset of zero would be used. Since this is the default value, you
  would not need to actually use the command at all.

  3.2.2.  The `load_ramdisk=' Argument

  This parameter tells the kernel whether it is to try to load a ramdisk
  image or not. Specifying `load_ramdisk=1' will tell the kernel to load
  a floppy into the ramdisk. The default value is zero, meaning that the
  kernel should not try to load a ramdisk.

  Please see the file linux/Documentation/ramdisk.txt for a complete
  description of the new boot time arguments, and how to use them. A
  description of how this parameter can be set and stored in the kernel
  image via `rdev' is also described.

  3.2.3.  The `prompt_ramdisk=' Argument

  This parameter tells the kernel whether or not to give you a prompt
  asking you to insert the floppy containing the ramdisk image. In a
  single floppy configuration the ramdisk image is on the same floppy as
  the kernel that just finished loading/booting and so a prompt is not
  needed. In this case one can use `prompt_ramdisk=0'. In a two floppy
  configuration, you will need the chance to switch disks, and thus
  `prompt_ramdisk=1' can be used. Since this is the default value, it
  doesn't really need to be specified. ( (Historical note: Sneaky people
  used to use the `vga=ask' LILO option to temporarily pause the boot
  process and allow a chance to switch from boot to root floppy.)

  Please see the file linux/Documentation/ramdisk.txt for a complete
  description of the new boot time arguments, and how to use them. A
  description of how this parameter can be set and stored in the kernel
  image via `rdev' is also described.

  3.2.4.  The `ramdisk_size=' Argument

  While it is true that the ramdisk grows dynamically as required, there
  is an upper bound on its size so that it doesn't consume all available
  RAM and leave you in a mess. The default is 4096 (i.e. 4MB) which
  should be large enough for most needs. You can override the default to
  a bigger or smaller size with this boot argument.

  Please see the file linux/Documentation/ramdisk.txt for a complete
  description of the new boot time arguments, and how to use them. A
  description of how this parameter can be set and stored in the kernel
  image via `rdev' is also described.

  3.2.5.  The `ramdisk=' Argument (obsolete)

  (NOTE: This argument is obsolete, and should not be used except on
  kernels v1.3.47 and older. The commands that should be used for the
  ramdisk device are documented above.)

  This specifies the size in kB of the 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.

  3.2.6.  The `noinitrd' (initial RAM disk) Argument

  The v2.x and newer kernels have a feature where the root filesystem is
  initially a RAM disk, and the kernel executes /linuxrc on that RAM
  image. This feature is typically used to allow loading of modules
  needed to mount the real root filesystem (e.g. load the SCSI driver
  modules stored in the RAM disk image, and then mount the real root
  filesystem on a SCSI disk.)

  The actual `noinitrd' argument determines what happens to the initrd
  data after the kernel has booted.  When specified, instead of
  converting it to a RAM disk, it is accessible via /dev/initrd, which
  can be read once before the RAM is released back to the system. For
  full details on using the initial RAM disk, please consult
  linux/Documentation/initrd.txt. In addition, the most recent versions
  of LILO and LOADLIN should have additional useful information.

  3.3.  Boot Arguments Related to Memory Handling

  The following arguments alter how linux detects or handles the
  physical and virtual memory of your system.

  3.3.1.  The `mem=' Argument

  This argument has two purposes: The original purpose was to specify
  the amount of installed memory (or a value less than that if you
  wanted to limit the amount of memory available to linux). The second
  (and hardly used) purpose is to specify mem=nopentium which tells the
  linux kernel to not use the 4MB page table performance feature.

  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 argument 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.

  3.3.2.  The `swap=' Argument

  This allows the user to tune some of the virtual memory (VM)
  parameters that are related to swapping to disk. It accepts the
  following eight parameters:

  ______________________________________________________________________
          MAX_PAGE_AGE
          PAGE_ADVANCE
          PAGE_DECLINE
          PAGE_INITIAL_AGE
          AGE_CLUSTER_FRACT
          AGE_CLUSTER_MIN
          PAGEOUT_WEIGHT
          BUFFEROUT_WEIGHT
  ______________________________________________________________________

  Interested hackers are advised to have a read of linux/mm/swap.c and
  also make note of the goodies in /proc/sys/vm.

  3.3.3.  The `buff=' Argument

  Similar to the `swap=' argument, this allows the user to tune some of
  the parameters related to buffer memory management.  It accepts the
  following six parameters:

  ______________________________________________________________________
          MAX_BUFF_AGE
          BUFF_ADVANCE
          BUFF_DECLINE
          BUFF_INITIAL_AGE
          BUFFEROUT_WEIGHT
          BUFFERMEM_GRACE
  ______________________________________________________________________

  Interested hackers are advised to have a read of linux/mm/swap.c and
  also make note of the goodies in /proc/sys/vm.

  3.4.  Boot Arguments for NFS Root Filesystem

  Linux supports systems such as diskless workstations via having their
  root filesystem as NFS (Network FileSystem).  These arguments are used
  to tell the diskless workstation which machine it is to get its system
  from. Also note that the argument root=/dev/nfs is required. Detailed
  information on using an NFS root fs is in the file
  linux/Documentation/nfsroot.txt. You should read that file, as the
  following is only a quick summary taken directly from that file.

  3.4.1.  The `nfsroot=' Argument

  This argument tells the kernel which machine, what directory and what
  NFS options to use for the root filesystem. The form of the argument
  is as follows:

  ______________________________________________________________________
          nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>]
  ______________________________________________________________________

  If the nfsroot parameter is not given on the command line, the default
  `/tftpboot/%s' will be used. The other options are as follows:

  <server-ip> -- Specifies the IP address of the NFS server. If this
  field is not given, the default address as determined by the nfsaddrs
  variable (see below) is used. One use of this parameter is for example
  to allow using different servers for RARP and NFS. Usually you can
  leave this blank.

  <root-dir> -- Name of the directory on the server to mount as root. If
  there is a `%s' token in the string, the token will be replaced by the
  ASCII-representation of the client's IP address.

  <nfs-options> -- Standard NFS options. All options are separated by
  commas.  If the options field is not given, the following defaults
  will be used:

          port            = as given by server portmap daemon
          rsize           = 1024
          wsize           = 1024
          timeo           = 7
          retrans         = 3
          acregmin        = 3
          acregmax        = 60
          acdirmin        = 30
          acdirmax        = 60
          flags           = hard, nointr, noposix, cto, ac

  3.4.2.  The `nfsaddrs=' Argument

  This boot argument sets up the various network interface addresses
  that are required to communicate over the network. If this argument is
  not given, then the kernel tries to use RARP and/or BOOTP to figure
  out these parameters. The form is as follows:

  ______________________________________________________________________
          nfsaddrs=<my-ip>:<serv-ip>:<gw-ip>:<netmask>:<name>:<dev>:<auto>
  ______________________________________________________________________

  <my-ip> -- IP address of the client. If empty, the address will either
  be determined by RARP or BOOTP. What protocol is used de- pends on
  what has been enabled during kernel configuration and on the <auto>
  parameter. If this parameter is not empty, neither RARP nor BOOTP will
  be used.

  <serv-ip> -- IP address of the NFS server. If RARP is used to
  determine the client address and this parameter is NOT empty only
  replies from the specified server are accepted. To use different RARP
  and NFS server, specify your RARP server here (or leave it blank), and
  specify your NFS server in the nfsroot parameter (see above). If this
  entry is blank the address of the server is used which answered the
  RARP or BOOTP request.

  <gw-ip> -- IP address of a gateway if the server in on a different
  subnet. If this entry is empty no gateway is used and the server is
  assumed to be on the local network, unless a value has been received
  by BOOTP.

  <netmask> -- Netmask for local network interface. If this is empty,
  the netmask is derived from the client IP address, unless a value has
  been received by BOOTP.

  <name> -- Name of the client. If empty, the client IP address is used
  in ASCII-notation, or the value received by BOOTP.

  <dev> -- Name of network device to use. If this is empty, all devices
  are used for RARP requests, and the first one found for BOOTP. For NFS
  the device is used on which either RARP or BOOTP replies have been
  received. If you only have one device you can safely leave this blank.

  <auto> -- Method to use for autoconfiguration. If this is either
  `rarp' or `bootp' the specified protocol is being used.  If the value
  is `both' or empty, both protocols are used so far as they have been
  enabled during kernel configuration Using 'none' means no
  autoconfiguration. In this case you have to specify all necessary
  values in the fields before.
  The <auto> parameter can appear alone as the value to the nfsaddrs
  parameter (without all the `:' characters before) in which case
  autoconfiguration is used. However, the `none' value is not available
  in that case.

  3.5.  Other Misc. Kernel Boot Arguments

  These various boot arguments let the user tune certain internal kernel
  parameters.

  3.5.1.  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.

  3.5.2.  The `init=' Argument

  The kernel defaults to starting the `init' program at boot, which then
  takes care of setting up the computer for users via launching getty
  programs, running `rc' scripts and the like.  The kernel first looks
  for /sbin/init, then /etc/init (depreciated), and as a last resort, it
  will try to use /bin/sh (possibly on /etc/rc).  If for example, your
  init program got corrupted and thus stopped you from being able to
  boot, you could simply use the boot prompt init=/bin/sh which would
  drop you directly into a shell at boot, allowing you to replace the
  corrupted program.

  3.5.3.  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,
  apparently due to a bug in the FRSAV/FRRESTOR instructions.  Using the
  `no387' boot argument causes Linux to ignore the math coprocessor even
  if you have one. Of course you must then have your kernel compiled
  with math emulation support! This may also be useful if you have one
  of those really old 386 machines that could use an 80287 FPU, as linux
  can't use an 80287.

  3.5.4.  The `no-hlt' Argument

  The i386 (and successors 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.

  3.5.5.  The `no-scroll' Argument

  Using this argument at boot disables scrolling features that make it
  difficult to use Braille terminals.

  3.5.6.  The `panic=' Argument

  In the unlikely event of a kernel panic (i.e. an internal error that
  has been detected by the kernel, and which the kernel decides is
  serious enough to moan loudly and then halt everything), the default
  behaviour is to just sit there until someone comes along and notices
  the panic message on the screen and reboots the machine.  However if a
  machine is running unattended in an isolated location it may be
  desirable for it to automatically reset itself so that the machine
  comes back on line. For example, using panic=30 at boot would cause
  the kernel to try and reboot itself 30 seconds after the kernel panic
  happened. A value of zero gives the default behaviour, which is to
  wait forever.

  Note that this timeout value can also be read and set via the
  /proc/sys/kernel/panic sysctl interface.

  3.5.7.  The `profile=' Argument

  Kernel developers can enable an option that allows them to profile how
  and where the kernel is spending its CPU cycles in an effort to
  maximize efficiency and performance. This option lets you set the
  profile shift count at boot. Typically it is set to two. You can also
  compile your kernel with profiling enabled by default. In either case,
  you need a tool such as readprofile.c that can make use of the
  /proc/profile output.

  3.5.8.  The `reboot=' Argument

  This option controls the type of reboot that Linux will do when it
  resets the computer (typically via /sbin/init handling a Control-Alt-
  Delete). The default as of late v2.0 kernels is to do a `cold' reboot
  (i.e. full reset, BIOS does memory check, etc.) instead of a `warm'
  reboot (i.e. no full reset, no memory check). It was changed to be
  cold by default since that tends to work on cheap/broken hardware that
  fails to reboot when a warm reboot is requested. To get the old
  behaviour (i.e. warm reboots) use reboot=w or in fact any word that
  starts with w will work.

  Why would you bother? Some disk controllers with cache memory on board
  can sense a warm reboot, and flush any cached data to disk. Upon a
  cold boot, the card may be reset and the write-back data in your cache
  card's memory is lost. Others have reported systems that take a long
  time to go through the memory check, and/or SCSI BIOSes that take
  longer to initialize on a cold boot as a good reason to use warm
  reboots.

  3.5.9.  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 (with the name reserved).  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 that do a check_region() prior to probing blindly into a region
  of I/O space. 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.

  3.5.10.  The `vga=' Argument

  Note that this is not really a boot argument. It is an option that is
  interpreted by LILO and not by the kernel like all the other boot
  arguments are. However its use has become so common that it deserves a
  mention here. It can also be set via using rdev -v or equivalently
  vidmode on the vmlinuz file.  This allows the setup code to use the
  video BIOS to change the default display mode before actually booting
  the Linux kernel. Typical modes are 80x50, 132x44 and so on. The best
  way to use this option is to start with vga=ask which will prompt you
  with a list of various modes that you can use with your video adapter
  before booting the kernel. Once you have the number from the above
  list that you want to use, you can later put it in place of the `ask'.
  For more information, please see the file linux/Documentation/svga.txt
  that comes with all recent kernel versions.

  Note that newer kernels (v2.1 and up) have the setup code that changes
  the video mode as an option, listed as Video mode selection support so
  you need to enable this option if you want to use this feature.

  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.

  4.1.  Arguments for Mid-level Drivers

  The mid level drivers handle things like disks, CD-ROMs and tapes
  without getting into host adapter specifics.

  4.1.1.  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

  4.1.2.  Parameters for the SCSI Tape Driver (`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 first 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.

  4.2.  Arguments for SCSI Host Adapters

  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 dependent 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 peripherals like IDE hard disks, floppies, serial
  ports, etc.

  dma -- the DMA (Direct Memory Access) channel that the card uses.
  Typically only applies to bus-mastering cards.  PCI and VLB cards are
  native bus-masters, and do not require and ISA DMA channel.

  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.

  4.2.1.  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 argument 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.

  4.2.2.  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 argument 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.

  4.2.3.  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.

  4.2.4.  AdvanSys SCSI Host Adaptors (`advansys=')

  The AdvanSys driver can accept up to four i/o addresses that will be
  probed for an AdvanSys SCSI card. Note that these values (if used) do
  not effect EISA or PCI probing in any way.  They are only used for
  probing ISA and VLB cards.  In addition, if the driver has been
  compiled with debugging enabled, the level of debugging output can be
  set by adding an 0xdeb[0-f] parameter. The 0-f allows setting the
  level of the debugging messages to any of 16 levels of verbosity.

  4.2.5.  Always IN2000 Host Adaptor (`in2000=')

  Unlike other SCSI host boot arguments, the IN2000 driver uses ASCII
  string prefixes for most of its integer arguments. Here is a list of
  the supported arguments:

  ioport:addr -- Where addr is IO address of a (usually ROM-less) card.

  noreset -- No optional args. Prevents SCSI bus reset at boot time.

  nosync:x -- x is a bitmask where the 1st 7 bits correspond with the 7
  possible SCSI devices (bit 0 for device #0, etc).  Set a bit to
  PREVENT sync negotiation on that device.  The driver default is sync
  DISABLED on all devices.

  period:ns -- ns is the minimum # of nanoseconds in a SCSI data
  transfer period. Default is 500; acceptable values are 250 to 1000.

  disconnect:x -- x = 0 to never allow disconnects, 2 to always allow
  them.  x = 1 does 'adaptive' disconnects, which is the default and
  generally the best choice.

  debug:x If `DEBUGGING_ON' is defined, x is a bitmask that causes
  various types of debug output to printed - see the DB_xxx defines in
  in2000.h

  proc:x -- If `PROC_INTERFACE' is defined, x is a bitmask that
  determines how the /proc interface works and what it does - see the
  PR_xxx defines in in2000.h

  Some example usages are listed below:

  ______________________________________________________________________
          in2000=ioport:0x220,noreset
          in2000=period:250,disconnect:2,nosync:0x03
          in2000=debug:0x1e
          in2000=proc:3
  ______________________________________________________________________

  4.2.6.  AMD AM53C974 based hardware (`AM53C974=')

  Unlike other drivers, this one does not use boot parameters to
  communicate i/o, IRQ or DMA channels. (Since the AM53C974 is a PCI
  device, there shouldn't be a need to do so.)  Instead, the parameters
  are used to communicate the transfer modes and rates that are to be
  used between the host and the target device. This is best described
  with an example:

  ______________________________________________________________________
          AM53C974=7,2,8,15
  ______________________________________________________________________

  This would be interpreted as follows: `For communication between the
  controller with SCSI-ID 7 and the device with SCSI-ID 2, a transfer
  rate of 8MHz in synchronous mode with max. 15 bytes offset should be
  negotiated.' More details can be found in the file
  linux/drivers/scsi/README.AM53C974

  4.2.7.  BusLogic SCSI Hosts with v1.2 kernels (`buslogic=')

  In older kernels, 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.

  4.2.8.  BusLogic SCSI Hosts with v2.x kernels (`BusLogic=')

  With v2.x kernels, the BusLogic driver accepts many parameters.  (Note
  the case in the above; upper case B and L!!!).  The following detailed
  description is taken directly from Leonard N. Zubkoff's driver as
  included in the v2.0 kernel.

  For the BusLogic driver, a Kernel command line entry comprises the
  driver identifier "BusLogic=" optionally followed by a comma-separated
  sequence of integers and then optionally followed by a comma-separated
  sequence of strings.  Each command line entry applies to one BusLogic
  Host Adapter.  Multiple command line entries may be used in systems
  which contain multiple BusLogic Host Adapters.

  The first integer specified is the I/O Address at which the Host
  Adapter is located.  If unspecified, it defaults to 0 which means to
  apply this entry to the first BusLogic Host Adapter found during the
  default probe sequence.  If any I/O Address parameters are provided on
  the command line, then the default probe sequence is omitted.

  The second integer specified is the Tagged Queue Depth to use for
  Target Devices that support Tagged Queuing.  The Queue Depth is the
  number of SCSI commands that are allowed to be concurrently presented
  for execution.  If unspecified, it defaults to 0 which means to use a
  value determined automatically based on the Host Adapter's Total Queue
  Depth and the number, type, speed, and capabilities of the detected
  Target Devices.  For Host Adapters that require ISA Bounce Buffers,
  the Tagged Queue Depth is automatically set to
  BusLogic_TaggedQueueDepth_BB to avoid excessive preallocation of DMA
  Bounce Buffer memory.  Target Devices that do not support Tagged
  Queuing use a Queue Depth of BusLogic_UntaggedQueueDepth.

  The third integer specified is the Bus Settle Time in seconds.  This
  is the amount of time to wait between a Host Adapter Hard Reset which
  initiates a SCSI Bus Reset and issuing any SCSI Commands.  If
  unspecified, it defaults to 0 which means to use the value of
  BusLogic_DefaultBusSettleTime.

  The fourth integer specified is the Local Options.  If unspecified, it
  defaults to 0.  Note that Local Options are only applied to a specific
  Host Adapter.

  The fifth integer specified is the Global Options.  If unspecified, it
  defaults to 0.  Note that Global Options are applied across all Host
  Adapters.

  The string options are used to provide control over Tagged Queuing,
  Error Recovery, and Host Adapter Probing.

  The Tagged Queuing specification begins with "TQ:" and allows for
  explicitly specifying whether Tagged Queuing is permitted on Target
  Devices that support it.  The following specification options are
  available:

  TQ:Default -- Tagged Queuing will be permitted based on the firmware
  version of the BusLogic Host Adapter and based on whether the Tagged
  Queue Depth value allows queuing multiple commands.

  TQ:Enable -- Tagged Queuing will be enabled for all Target Devices on
  this Host Adapter overriding any limitation that would otherwise be
  imposed based on the Host Adapter firmware version.

  TQ:Disable -- Tagged Queuing will be disabled for all Target Devices
  on this Host Adapter.

  TQ:<Per-Target-Spec> -- Tagged Queuing will be controlled individually
  for each Target Device. <Per-Target-Spec> is a sequence of "Y", "N",
  and "X" characters.  "Y" enabled Tagged Queuing, "N" disables Tagged
  Queuing, and "X" accepts the default based on the firmware version.
  The first character refers to Target Device 0, the second to Target
  Device 1, and so on; if the sequence of "Y", "N", and "X" characters
  does not cover all the Target Devices, unspecified characters are
  assumed to be "X".

  Note that explicitly requesting Tagged Queuing may lead to problems;
  this facility is provided primarily to allow disabling Tagged Queuing
  on Target Devices that do not implement it correctly.

  The Error Recovery Strategy specification begins with "ER:" and allows
  for explicitly specifying the Error Recovery action to be performed
  when ResetCommand is called due to a SCSI Command failing to complete
  successfully.  The following specification options are available:

  ER:Default -- Error Recovery will select between the Hard Reset and
  Bus Device Reset options based on the recommendation of the SCSI
  Subsystem.

  ER:HardReset -- Error Recovery will initiate a Host Adapter Hard Reset
  which also causes a SCSI Bus Reset.

  ER:BusDeviceReset -- Error Recovery will send a Bus Device Reset
  message to the individual Target Device causing the error.  If Error
  Recovery is again initiated for this Target Device and no SCSI Command
  to this Target Device has completed successfully since the Bus Device
  Reset message was sent, then a Hard Reset will be attempted.

  ER:None -- Error Recovery will be suppressed.  This option should only
  be selected if a SCSI Bus Reset or Bus Device Reset will cause the
  Target Device to fail completely and unrecoverably.

  ER:<Per-Target-Spec> -- Error Recovery will be controlled individually
  for each Target Device. <Per-Target-Spec> is a sequence of "D", "H",
  "B", and "N" characters.  "D" selects Default, "H" selects Hard Reset,
  "B" selects Bus Device Reset, and "N" selects None.  The first
  character refers to Target Device 0, the second to Target Device 1,
  and so on; if the sequence of "D", "H", "B", and "N" characters does
  not cover all the possible Target Devices, unspecified characters are
  assumed to be "D".

  The Host Adapter Probing specification comprises the following
  strings:

  NoProbe -- No probing of any kind is to be performed, and hence no
  BusLogic Host Adapters will be detected.

  NoProbeISA -- No probing of the standard ISA I/O Addresses will be
  done, and hence only PCI Host Adapters will be detected.

  NoSortPCI -- PCI Host Adapters will be enumerated in the order
  provided by the PCI BIOS, ignoring any setting of the AutoSCSI "Use
  Bus And Device # For PCI Scanning Seq." option.

  4.2.9.  EATA SCSI Cards (`eata=')

  As of late v2.0 kernels, the EATA drivers will accept a boot argument
  to specify the i/o base(s) to be probed. It is of the form:

  ______________________________________________________________________
          eata=iobase1[,iobase2][,iobase3]...[,iobaseN]
  ______________________________________________________________________

  The driver will probe the addresses in the order that they are listed.

  4.2.10.  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 recognized then it will also not
  be found. In either case, you will then have to use a boot argument 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.

  4.2.11.  Future Domain TMC-16xx, TMC-3260, AHA-2920 (`fdomain=')

  The driver detects these cards according to a list of known BIOS ROM
  signatures. For a full list of known BIOS revisions, please see
  linux/drivers/scsi/fdomain.c as it has a lot of information at the top
  of that file. If your BIOS is not known to the driver, you can use an
  override of the form:

  ______________________________________________________________________
          fdomain=iobase,irq[,scsi_id]
  ______________________________________________________________________

  4.2.12.  IOMEGA Parallel Port / ZIP drive (`ppa=')

  This driver is for the IOMEGA Parallel Port SCSI adapter which is
  embedded into the IOMEGA ZIP drives. It may also work with the
  original IOMEGA PPA3 device. The boot argument for this driver is of
  the form:

  ______________________________________________________________________
          ppa=iobase,speed_high,speed_low,nybble
  ______________________________________________________________________

  with all but iobase being optionally specified values. If you wish to
  alter any of the three optional parameters, you are advised to read
  linux/drivers/scsi/README.ppa for details of what they control.

  4.2.13.  NCR5380 based controllers (`ncr5380=')

  Depending on your board, the 5380 can be either i/o mapped or memory
  mapped. (An address below 0x400 usually implies i/o mapping, but PCI
  and EISA hardware use i/o addresses above 0x3ff.) In either case, you
  specify the address, the IRQ value and the DMA channel value. An
  example for an i/o mapped card would be: ncr5380=0x350,5,3. If the
  card doesn't use interrupts, then an IRQ value of 255 (0xff) will
  disable interrupts. An IRQ value of 254 means to autoprobe. More
  details can be found in the file linux/drivers/scsi/README.g_NCR5380

  4.2.14.  NCR53c400 based controllers (`ncr53c400=')

  The generic 53c400 support is done with the same driver as the generic
  5380 support mentioned above. The boot argument is identical to the
  above with the exception that no DMA channel is used by the 53c400.

  4.2.15.  NCR53c406a based controllers (`ncr53c406a=')

  This driver uses a boot argument of the form:

  ______________________________________________________________________
          ncr53c406a=PORTBASE,IRQ,FASTPIO
  ______________________________________________________________________

  where the IRQ and FASTPIO parameters are optional. An interrupt value
  of zero disables the use of interrupts. Using a value of one for the
  FASTPIO parameter enables the use of insl and outsl instructions
  instead of the single-byte inb and outb instructions. The driver can
  also use DMA as a compile-time option.

  4.2.16.  Pro Audio Spectrum (`pas16=')

  The PAS16 uses a NCR5380 SCSI chip, and newer models support jumper-
  less configuration. The boot argument 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.

  4.2.17.  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 recognized then it will also not
  be found. In either case, you will then have to use a boot argument 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.

  4.2.18.  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.

  4.2.19.  Ultrastor SCSI cards (`u14-34f=')

  Note that there appears to be two independent drivers for this card,
  namely CONFIG_SCSI_U14_34F that uses u14-34f.c and
  CONFIG_SCSI_ULTRASTOR that uses ultrastor.c. It is the u14-34f one
  that (as of late v2.0 kernels) accepts a boot argument of the form:

  ______________________________________________________________________
          u14-34f=iobase1[,iobase2][,iobase3]...[,iobaseN]
  ______________________________________________________________________

  The driver will probe the addresses in the order that they are listed.

  4.2.20.  Western Digital WD7000 cards (`wd7000=')

  The driver probe for the wd7000 looks for a known BIOS ROM string and
  knows about a few standard configuration settings.  If it doesn't come
  up with the correct values for your card, or you have an unrecognized
  BIOS version, you can use a boot argument of the form:

  ______________________________________________________________________
          wd7000=irq,dma,iobase
  ______________________________________________________________________

  4.3.  SCSI Host Adapters 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.

          Adaptec aha1740 (EISA probing),
          NCR53c7xx,8xx (PCI, both drivers)
          Qlogic Fast (0x230, 0x330)
          Qlogic ISP (PCI)

  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 advanced or broken controller
  chips. The following is a summary of all the possible boot arguments.
  For full details, you really should consult the file ide.txt in the
  linux/Documentation directory, from which this summary was extracted.

  ______________________________________________________________________

   "hdx="  is recognized for all "x" from "a" to "h", such as "hdc".
   "idex=" is recognized for all "x" from "0" to "3", such as "ide1".

   "hdx=noprobe"          : drive may be present, but do not probe for it
   "hdx=none"             : drive is NOT present, ignore cmos and do not probe
   "hdx=nowerr"           : ignore the WRERR_STAT bit on this drive
   "hdx=cdrom"            : drive is present, and is a cdrom drive
   "hdx=cyl,head,sect"    : disk drive is present, with specified geometry
   "hdx=autotune"         : driver will attempt to tune interface speed
                                  to the fastest PIO mode supported,
                                  if possible for this drive only.
                                  Not fully supported by all chipset types,
                                  and quite likely to cause trouble with
                                  older/odd IDE drives.

   "idex=noprobe"         : do not attempt to access/use this interface
   "idex=base"            : probe for an interface at the addr specified,
                                  where "base" is usually 0x1f0 or 0x170
                                  and "ctl" is assumed to be "base"+0x206
   "idex=base,ctl"        : specify both base and ctl
   "idex=base,ctl,irq"    : specify base, ctl, and irq number
   "idex=autotune"        : driver will attempt to tune interface speed
                                  to the fastest PIO mode supported,
                                  for all drives on this interface.
                                  Not fully supported by all chipset types,
                                  and quite likely to cause trouble with
                                  older/odd IDE drives.
   "idex=noautotune"      : driver will NOT attempt to tune interface speed
                                  This is the default for most chipsets,
                                  except the cmd640.
   "idex=serialize"       : do not overlap operations on idex and ide(x^1)
  ______________________________________________________________________

  The following are valid ONLY on ide0, and the defaults for the
  base,ctl ports must not be altered.

  ______________________________________________________________________

   "ide0=dtc2278"         : probe/support DTC2278 interface
   "ide0=ht6560b"         : probe/support HT6560B interface
   "ide0=cmd640_vlb"      : *REQUIRED* for VLB cards with the CMD640 chip
                            (not for PCI -- automatically detected)
   "ide0=qd6580"          : probe/support qd6580 interface
   "ide0=ali14xx"         : probe/support ali14xx chipsets (ALI M1439/M1445)
   "ide0=umc8672"         : probe/support umc8672 chipsets
  ______________________________________________________________________

  Everything else is rejected with a "BAD OPTION" message.

  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 recognized then it will also not be found.
  In either case, you will then have to use a boot argument 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.

  Note that most of these CD-ROMs have documentation files that you
  should read, and they are all in one handy place:
  linux/Documentation/cdrom.
  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 ISP16 Interface (`isp16=')

  The syntax for this CD-ROM interface is:

  ______________________________________________________________________
          isp16=[port[,irq[,dma]]][[,]drive_type]
  ______________________________________________________________________

  Using a zero for irq or dma means that they are not used. The
  allowable values for drive_type are noisp16, Sanyo, Panasonic, Sony,
  and Mitsumi.  Using noisp16 disables the driver altogether.

  6.6.  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.

  6.7.  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.

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

  The syntax for this type of card is:

  ______________________________________________________________________
          optcd=iobase
  ______________________________________________________________________

  6.9.  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.

  6.10.  The Sanyo Interface (`sjcd=')

  The syntax for this type of card is:

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

  6.11.  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.

  IMPORTANT NOTE TO MODULE USERS: The above will not force a probe for a
  second card if you are using the driver(s) as run time loadable
  modules (instead of having them complied into the kernel).  Most Linux
  distributions use a bare bones kernel combined with a large selection
  of modular drivers.  The ether= only applies to drivers compiled
  directly into the kernel.

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

  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.

  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.

  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.

  floppy=asus_pci

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

  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.

  floppy=0,daring

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

  floppy=one_fdc

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

  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.

  floppy=thinkpad

  Tells the floppy driver that you have a Thinkpad. Thinkpads use an
  inverted convention for the disk change line.

  floppy=0,thinkpad

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

  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.

  floppy=unexpected_interrupts

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

  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 (was?)
  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.

  7.5.  The MS Bus Mouse Driver (`msmouse=')

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

  7.6.  The Printer Driver (`lp=')

  As of kernels newer than 1.3.75, you can tell the printer driver what
  ports to use and what ports not to use. The latter comes in handy if
  you don't want the printer driver to claim all available parallel
  ports, so that other drivers (e.g. PLIP, PPA) can use them instead.

  The format of the argument is multiple i/o, IRQ pairs. For example,
  lp=0x3bc,0,0x378,7 would use the port at 0x3bc in IRQ-less (polling)
  mode, and use IRQ 7 for the port at 0x378. The port at 0x278 (if any)
  would not be probed, since autoprobing only takes place in the absence
  of a `lp=' argument. To disable the printer driver entirely, one can
  use lp=0.

  7.7.  The ICN ISDN driver (`icn=')

  This ISDN driver expects a boot argument of the form:

  ______________________________________________________________________
          icn=iobase,membase,icn_id1,icn_id2
  ______________________________________________________________________

  where iobase is the i/o port address of the card, membase is the
  shared memory base address of the card, and the two icn_id are unique
  ASCII string identifiers.

  7.8.  The PCBIT ISDN driver (`pcbit=')

  This boot argument takes integer pair arguments of the form:

  ______________________________________________________________________
          pcbit=membase1,irq1[,membase2,irq2]
  ______________________________________________________________________

  where membaseN is the shared memory base of the N'th card, and irqN is
  the interrupt setting of the N'th card. The default is IRQ 5 and
  membase 0xD0000.

  7.9.  The Teles ISDN driver (`teles=')

  This ISDN driver expects a boot argument of the form:

  ______________________________________________________________________
          teles=iobase,irq,membase,protocol,teles_id
  ______________________________________________________________________

  where iobase is the i/o port address of the card, membase is the
  shared memory base address of the card, irq is the interrupt channel
  the card uses, and teles_id is the unique ASCII string identifier.

  7.10.  The DigiBoard Driver (`digi=')

  The DigiBoard driver accepts a string of six comma separated
  identifiers or integers.  The 6 values in order are:

          Enable/Disable this card
          Type of card: PC/Xi(0), PC/Xe(1), PC/Xeve(2), PC/Xem(3)
          Enable/Disable alternate pin arrangement
          Number of ports on this card
          I/O Port where card is configured (in HEX if using string identifiers)
          Base of memory window (in HEX if using string identifiers)

  An example of a correct boot prompt argument (in both identifier and
  integer form) is:

  ______________________________________________________________________
          digi=E,PC/Xi,D,16,200,D0000
          digi=1,0,0,16,512,851968
  ______________________________________________________________________

  Note that the driver defaults to an i/o of 0x200 and a shared memory
  base of 0xD0000 in the absence of a digi= boot argument.  There is no
  autoprobing performed. More details can be found in the file
  linux/Documentation/digiboard.txt.

  7.11.  The RISCom/8 Multiport Serial Driver (`riscom8=')

  Up to four boards can be supported by supplying four unique i/o port
  values for each individual board installed.  Other details can be
  found in the file linux/Documentation/riscom8.txt.

  7.12.  The Baycom Serial/Parallel Radio Modem (`baycom=')

  The format of the boot argument for these devices is:

  ______________________________________________________________________
          baycom=modem,io,irq,options[,modem,io,irq,options]
  ______________________________________________________________________

  Using modem=1 means you have the ser12 device, modem=2 means you have
  the par96 device. Using options=0 means use hardware DCD, and
  options=1 means use software DCD. The io and irq are the i/o port base
  and interrupt settings as usual.  There is more details in the file
  README.baycom which is currently in the /linux/drivers/char/
  directory.

  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]