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BOOTPARAM(7)		   Linux Programmers Manual		 BOOTPARAM(7)

       bootparam - Introduction to boot time parameters of the Linux kernel

       The  Linux  kernel accepts certain command-line options or boot time
       parameters at the moment it is started.	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.

       When  the  kernel  is booted directly by the BIOS (say from a floppy to
       which you copied a kernel using cp  zImage  /dev/fd0),  you  have  no
       opportunity  to specify any parameters.	So, in order to take advantage
       of this possibility you have to use  software  that  is	able  to  pass
       parameters,  like  LILO	or loadlin.  For a few parameters one can also
       modify the kernel image itself, using rdev,  see  rdev(8)  for  further

       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.  (See
       lilo(8) and lilo.conf(5).)  LILO can boot DOS,  OS/2,  Linux,  FreeBSD,
       UnixWare, etc., and is quite flexible.

       The  other  commonly used Linux loader is LoadLin which is a DOS pro
       gram 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 want to launch 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  load
       ing Linux from the DOS prompt with loadlin avoids the reset of the card
       that happens if one rebooted instead.

   The Argument List
       The kernel command line is parsed into a list of  strings  (boot  argu
       ments) separated by spaces.  Most of the boot args take the form of:


       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.  Note the
       limit  of  10  is real, as the present code only handles 10 comma sepa
       rated parameters per keyword.  (However, you can re-use the  same  key
       word  with  up  to an additional 10 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
       checks  to see if the argument is any of the special arguments root=,
       nfsroot=, nfsaddrs=, ro, rw, debug or init.  The meaning of
       these special arguments is described below.

       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.

       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 argu

       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.

   General Non-device Specific Boot Arguments
	      This  sets the initial command to be executed by the kernel.  If
	      this is not set,	or  cannot  be	found,	the  kernel  will  try
	      /sbin/init,  then  /etc/init,  then  /bin/init, then /bin/sh and
	      panic if all of this fails.

	      This sets the nfs boot address to the given string.   This  boot
	      address is used in case of a net boot.

	      This sets the nfs root name to the given string.	If this string
	      does not begin with / or , or a digit, then it  is  prefixed
	      by  /tftpboot/.  This root name is used in case of a net boot.

	      (Only when CONFIG_BUGi386 is defined.)   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!

	      (Only when  CONFIG_BUGi386  is  defined.)   Some	of  the  early
	      i486DX-100  chips  have a problem with the hlt instruction, in
	      that they cant reliably return to  operating  mode  after  this
	      instruction is 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 the CPU.  This allows people with these broken
	      chips to use Linux.

	      This argument tells the kernel what device is to be used as  the
	      root  file system while booting.	The default of this setting is
	      determined at compile time, and usually is the value of the root
	      device  of the system that the kernel was built on.  To override
	      this value, and select the  second  floppy  drive  as  the  root
	      device,  one  would  use	root=/dev/fd1.	(The root device can
	      also be set using rdev(8).)

	      The root device can be specified symbolically or numerically.  A
	      symbolic	specification  has the form /dev/XXYN, where XX desig
	      nates the device type (hd for  ST-506  compatible  hard  disk,
	      with  Y  in  a-d;  sd  for SCSI compatible disk, with Y in
	      a-e; ad for Atari ACSI disk, with Y in a-e, ez for a
	      Syquest  EZ135  parallel	port removable drive, with Y=a, xd
	      for XT compatible disk, with Y  either  a  or  b;  fd  for
	      floppy  disk,  with Y the floppy drive number  fd0 would be the
	      DOS A: drive, and fd1 would be B:), Y the driver	letter	or
	      number,  and  N the number (in decimal) of the partition on this
	      device (absent in the case of floppies).	Recent	kernels  allow
	      many  other  types,  mostly  for	CD-ROMs:  nfs,	ram, scd, mcd,
	      cdu535, aztcd, cm206cd, gscd, sbpcd, sonycd,  bpcd.   (The  type
	      nfs specifies a net boot; ram refers to a ram disk.)

	      Note  that  this has nothing to do with the designation of these
	      devices on your file system.  The /dev/ part is purely conven

	      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.)

       ro and rw
	      The ro option tells the kernel to mount the root	file  system
	      as  read-only  so  that file system consistency check programs
	      (fsck) can do their work on a quiescent file  system.   No  pro
	      cesses  can  write to files on the file system in question until
	      it is remounted as read/write capable, for example, by  mount
	      -w -n -o remount /.  (See also mount(8).)

	      The  rw  option tells the kernel to mount the root file system
	      read/write.  This is the default.

	      The choice between read-only and	read/write  can  also  be  set
	      using rdev(8).

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


	      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 hardware that reacts badly to  the  prob
	      ing,  or hardware that would be mistakenly identified, or merely
	      hardware you dont want the kernel to initialize.

	      The reserve boot-time argument specifies an I/O port region that
	      shouldnt	be probed.  A device driver will not probe a reserved
	      region, unless another boot argument explicitly  specifies  that
	      it do so.

	      For example, the boot line

	      reserve=0x300,32	blah=0x300

	      keeps all device drivers except the driver for blah from prob
	      ing 0x300-0x31f.

	      The 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.  Linux uses this BIOS call at boot to	deter
	      mine  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.	The value is in decimal or hexadecimal
	      (prefix 0x), and the suffixes k (times  1024)  or  M  (times
	      1048576)	can  be  used.	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 hor
		   ribly 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 caching 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.

	      You can also use the boot argument mem=nopentium to turn off 4
	      MB page tables on kernels configured for	IA32  systems  with  a
	      pentium or newer CPU.

	      By  default  the	kernel will not reboot after a panic, but this
	      option will cause a kernel reboot  after	N  seconds  (if  N  is
	      greater than zero).  This panic timeout can also be set by "echo
	      N > /proc/sys/kernel/panic".

	      (Only when CONFIG_BUGi386 is defined.)  Since 2.0.22 a reboot is
	      by  default  a  cold  reboot.  One asks for the old default with
	      reboot=warm.  (A cold reboot may be required to reset  certain
	      hardware,  but  might  destroy  not  yet	written data in a disk
	      cache.  A warm reboot may be faster.)  By default  a  reboot  is
	      hard,  by asking the keyboard controller to pulse the reset line
	      low, but there is at least one type of  motherboard  where  that
	      doesnt  work.   The  option  reboot=bios	will  instead  jump
	      through the BIOS.

       nosmp and maxcpus=N
	      (Only when  __SMP__  is  defined.)   A  command-line  option  of
	      nosmp  or maxcpus=0 will disable SMP activation entirely; an
	      option maxcpus=N limits the maximum number of  CPUs  activated
	      in SMP mode to N.

   Boot Arguments for Use by Kernel Developers
	      Kernel messages are handed off to the kernel log daemon klogd so
	      that they may be logged to disk.	Messages with a priority above
	      console_loglevel	are  also  printed on the console.  (For these
	      levels, see .)  By default this variable is  set
	      to  log  anything more important than debug messages.  This boot
	      argument will cause the kernel to also  print  the  messages  of
	      DEBUG  priority.	 The  console  loglevel can also be set at run
	      time via an option to klogd.  See klogd(8).

	      It is possible to enable a kernel  profiling  function,  if  one
	      wishes  to find out where the kernel is spending its CPU cycles.
	      Profiling is enabled by setting the  variable  prof_shift  to  a
	      non-zero	value.	 This is done either by specifying CONFIG_PRO
	      FILE at compile time, or by giving the profile=  option.	 Now
	      the  value  that	prof_shift gets will be N, when given, or CON
	      FIG_PROFILE_SHIFT, when that is given, or 2, the	default.   The
	      significance  of	this variable is that it gives the granularity
	      of the profiling: each clock tick, if the system	was  executing
	      kernel code, a counter is incremented:

	      profile[address >> prof_shift]++;

	      The  raw	profiling  information can be read from /proc/profile.
	      Probably youll want to use a  tool  such	as  readprofile.c  to
	      digest it.  Writing to /proc/profile will clear the counters.

	      Set    the    eight   parameters	 max_page_age,	 page_advance,
	      page_decline,  page_initial_age,	age_cluster_fract,   age_clus
	      ter_min,	pageout_weight, bufferout_weight that control the ker
	      nel swap algorithm.  For kernel tuners only.

	      Set the six parameters max_buff_age, buff_advance, buff_decline,
	      buff_initial_age, bufferout_weight, buffermem_grace that control
	      kernel buffer memory management.	For kernel tuners only.

   Boot Arguments for Ramdisk Use
       (Only if the kernel was compiled with CONFIG_BLK_DEV_RAM.)  In  general
       it  is  a  bad  idea to use a ramdisk under Linux  the system will use
       available memory more efficiently itself.  But while booting (or  while
       constructing  boot floppies) it is often useful to load the floppy con
       tents into a ramdisk.  One might also have a system in which first some
       modules	(for  file  system or hardware) must be loaded before the main
       disk can be accessed.

       In Linux 1.3.48, ramdisk handling was  changed  drastically.   Earlier,
       the memory was allocated statically, and there was a ramdisk=N param
       eter to tell its size.  (This could also be set in the kernel image  at
       compile	time,  or  by  use  of rdev(8).)  These days ram disks use the
       buffer cache, and grow dynamically.  For a lot  of  information	(e.g.,
       how  to	use  rdev(8)  in  conjunction with the new ramdisk setup), see

       There are four parameters, two boolean and two integral.

	      If N=1, do load a ramdisk.  If  N=0,  do	not  load  a  ramdisk.
	      (This is the default.)

	      If  N=1,	do  prompt  for insertion of the floppy.  (This is the
	      default.)  If N=0, do not  prompt.   (Thus,  this  parameter  is
	      never needed.)

       ramdisk_size=N or (obsolete) ramdisk=N
	      Set  the maximal size of the ramdisk(s) to N kB.	The default is
	      4096 (4 MB).

	      Sets the starting block number (the offset on the  floppy  where
	      the  ramdisk  starts)  to N.  This is needed in case the ramdisk
	      follows a kernel image.

	      (Only if the kernel was  compiled  with  CONFIG_BLK_DEV_RAM  and
	      CONFIG_BLK_DEV_INITRD.)	These  days  it is possible to compile
	      the kernel to use initrd.  When this  feature  is  enabled,  the
	      boot  process  will load the kernel and an initial ramdisk; then
	      the kernel converts initrd into a  "normal"  ramdisk,  which  is
	      mounted  read-write  as  root device; then /linuxrc is executed;
	      afterwards the "real" root file system is mounted, and the  ini
	      trd file system is moved over to /initrd; finally the usual boot
	      sequence (e.g., invocation of /sbin/init) is performed.

	      For  a  detailed	description  of  the   initrd	feature,   see

	      The noinitrd option tells the kernel that although it was com
	      piled for operation with initrd, it should not  go  through  the
	      above steps, but leave the initrd data under /dev/initrd.  (This
	      device can be used only once: the data is freed as soon  as  the
	      last process that used it has closed /dev/initrd.)

   Boot Arguments for SCSI Devices
       General notation for this section:

       iobase  --  the	first I/O port that the SCSI host occupies.  These are
       specified in hexadecimal 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  usu
       ally 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,

       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 7, but the Seagate and Future Domain TMC-950 boards use 6.

       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 check
       ing.  Again, not all adapters will support selection of parity behavior
       as a boot argument.

	      A 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.

	      Some poorly designed SCSI devices cannot handle being probed for
	      LUNs not equal to zero.  Therefore,  if  the  compile-time  flag
	      CONFIG_SCSI_MULTI_LUN  is not set, newer kernels will by default
	      only probe LUN zero.

	      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.

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


	      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:


	      Full  details can be found in the file Documentation/scsi/st.txt
	      (or drivers/scsi/README.st for  older  kernels)  in  the	kernel

       Adaptec aha151x, aha152x, aic6260, aic6360, SB16-SCSI configuration
	      The  aha numbers refer to cards and the aic numbers refer to the
	      actual SCSI chip on these type of cards,	including  the	Sound
	      blaster-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:


	      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:


	      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.

       Adaptec aha154x configuration
	      The  aha1542  series  cards  have  an  i82077  floppy controller
	      onboard, while the aha1540 series cards do not.  These are  bus
	      mastering  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.


	      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.  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

       Adaptec aha274x, aha284x, aic7xxx configuration
	      These boards can accept an argument of the form:


	      The  extended value, if non-zero, indicates that extended trans
	      lation 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 adapter at boot.

       AdvanSys SCSI Hosts configuration (advansys=)
	      The AdvanSys driver can accept up to  four  i/o  addresses  that
	      will  be probed for an AdvanSys SCSI card.  Note that these val
	      ues (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.



       BusLogic SCSI Hosts configuration (BusLogic=)


	      For an extensive discussion of the BusLogic command line parame
	      ters,    see    /usr/src/linux/drivers/scsi/BusLogic.c	(lines
	      3149-3270  in  the  kernel  version  I am looking at).  The text
	      below is a very much abbreviated extract.

	      The parameters N1-N5 are integers.  The  parameters  S1,...  are
	      strings.	 N1  is  the  I/O Address at which the Host Adapter is
	      located.	N2 is the Tagged Queue Depth to use for Target Devices
	      that  support Tagged Queuing.  N3 is the Bus Settle Time in sec
	      onds.  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.  N4 is the Local Options (for one Host	Adapter).   N5
	      is the Global Options (for all Host Adapters).

	      The string options are used to provide control over Tagged Queu
	      ing (TQ:Default, TQ:Enable,  TQ:Disable,	TQ:),
	      over  Error  Recovery (ER:Default, ER:HardReset, ER:BusDeviceRe
	      set, ER:None, ER:), and over Host Adapter Prob
	      ing (NoProbe, NoProbeISA, NoSortPCI).

       EATA/DMA configuration
	      The default list of i/o ports to be probed can be changed by


       Future Domain TMC-16x0 configuration


       Great Valley Products (GVP) SCSI controller configuration


       Future Domain TMC-8xx, TMC-950 configuration


	      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.

       IN2000 configuration


	      where  S	is  a comma-separated string of items keyword[:value].
	      Recognized keywords  (possibly  with  value)  are:  ioport:addr,
	      noreset,	nosync:x,  period:ns,  disconnect:x,  debug:x, proc:x.
	      For    the     function	  of	 these	   parameters,	   see

       NCR5380 and NCR53C400 configuration
	      The boot arg is of the form




	      If  the  card  doesnt  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 Documenta
	      tion/scsi/g_NCR5380.txt  (or  drivers/scsi/README.g_NCR5380  for
	      older kernels) in the kernel source.

       NCR53C8xx configuration


	      where  S	is  a  comma-separated	string of items keyword:value.
	      Recognized keywords are: mpar (master_parity),  spar  (scsi_par
	      ity),  disc  (disconnection),  specf  (special_features),  ultra
	      (ultra_scsi), fsn (force_sync_nego), tags  (default_tags),  sync
	      (default_sync),	 verb	 (verbose),   debug   (debug),	 burst
	      (burst_max).  For the  function  of  the	assigned  values,  see

       NCR53c406a configuration


	      Specify  irq = 0 for non-interrupt driven mode.  Set fastpio = 1
	      for fast pio mode, 0 for slow mode.

       Pro Audio Spectrum configuration
	      The PAS16 uses a NC5380 SCSI  chip,  and	newer  models  support
	      jumperless configuration.  The boot arg is of the form:


	      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.

       Seagate ST-0x configuration
	      If your card is not detected at boot time, you will then have to
	      use a boot arg of the form:


	      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.

       Trantor T128 configuration
	      These cards are also based on the NCR5380 chip, and  accept  the
	      following options:


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

       UltraStor 14F/34F configuration
	      The default list of i/o ports to be probed can be changed by


       WD7000 configuration


       Commodore Amiga A2091/590 SCSI controller configuration


	      where S is a  comma-separated  string  of  options.   Recognized
	      options  are  nosync:bitmask,  nodma:x, period:ns, disconnect:x,
	      debug:x,	   clock:x,	next.	    For      details,	   see

   Hard Disks
       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 hdX=
	      with X in a-h.

	      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

	      Also  note  that hd= can be used to refer to the next unspeci
	      fied drive in the (a, ..., h) sequence.  For the following  dis
	      cussions,  the  hd= option will be cited for brevity.  See the
	      file  Documentation/ide.txt  (or	drivers/block/README.ide   for
	      older kernels) in the kernel source for more details.

       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	cylin
	      der/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.

       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.

       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

       The hd=noprobe option
	      Do not probe for this drive.  For example,

	      hdb=noprobe hdb=1166,7,17

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

       The hd=nowerr option
	      Some  drives  apparently have the WRERR_STAT bit stuck on perma
	      nently.  This enables a work-around for these broken devices.

       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  isnt  then
	      this may help.

       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  argu
	      ment,  that is, hda= and so on are not valid here.  The format
	      is as follows:


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

       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.   If  the	card is not recognized, you will have to use a
	      boot arg of the form:


	      The type value specifies	the  particular  manufacturer  of  the
	      card,  overriding  autodetection.  For the types to use, consult
	      the drivers/block/xd.c source file of the kernel you are	using.
	      The  type  is  an index in the list xd_sigs and in the course of
	      time types have been added to or deleted from the middle of  the
	      list,  changing all type numbers.  Today (Linux 2.5.0) the types
	      are 0=generic; 1=DTC 5150cx; 2,3=DTC 5150x; 4,5=Western Digital;
	      6,7,8=Seagate;  9=Omti;  10=XEBEC,  and where here several types
	      are given with the same designation, they are equivalent.

	      The xd_setup() function does no  checking  on  the  values,  and
	      assumes  that you entered all four values.  Dont disappoint it.
	      Here is an example usage for a WD1002 controller with  the  BIOS
	      disabled/removed, using the default XT controller parameters:


       Syquests EZ* removable disks


   IBM MCA Bus Devices
       See also /usr/src/linux/Documentation/mca.txt.

       PS/2 ESDI hard disks
	      It is possible to specify the desired geometry at boot time:


	      For a ThinkPad-720, add the option


       IBM Microchannel SCSI Subsystem configuration


	      where N is the pun (SCSI ID) of the subsystem.

       The Aztech Interface
	      The syntax for this type of card is:


	      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.

       Parallel port CD-ROM drives


	      where  port is the base address, pro is the protocol number,
	      uni is the unit selector (for chained devices), mod  is  the
	      mode  (or -1 to choose the best automatically), slv is 1 if it
	      should be a slave, and dly is a small integer for slowing down
	      port  accesses.	The nice parameter controls the drivers use
	      of idle CPU time, at the expense of some speed.

       The CDU-31A and CDU-33A Sony Interface
	      This CD-ROM interface is found on some of the Pro Audio Spectrum
	      sound  cards, and other Sony supplied interface cards.  The syn
	      tax is as follows:


	      Specifying an IRQ value of zero tells the driver	that  hardware
	      interrupts  arent  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.

       The CDU-535 Sony Interface
	      The syntax for this CD-ROM interface is:


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

       The GoldStar Interface
	      The syntax for this CD-ROM interface is:


       The ISP16 CD-ROM Interface


	      (three integers  and  a  string).   If  the  type  is  given  as
	      noisp16,	the  interface will not be configured.	Other recog
	      nized types are: Sanyo", Sony, Panasonic and Mitsumi.

       The Mitsumi Standard Interface
	      The syntax for this CD-ROM interface is:


	      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.   The  Mitsumi
	      FX400  is  an  IDE/ATAPI	CD-ROM player and does not use the mcd

       The Mitsumi XA/MultiSession Interface
	      This is for the same hardware  as  above,  but  the  driver  has
	      extended features.  Syntax:


       The Optics Storage Interface
	      The syntax for this type of card is:


       The Phillips CM206 Interface
	      The syntax for this type of card is:


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

       The Sanyo Interface
	      The syntax for this type of card is:


       The SoundBlaster Pro Interface
	      The syntax for this type of card is:


	      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

   Ethernet Devices
       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:


	      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	selec
	      tion, 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:


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

	      The Ethernet-HowTo has 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.

   The Floppy Disk Driver
       There  are many floppy driver options, and they are all listed in Docu
       mentation/floppy.txt (or drivers/block/README.fd for older kernels)  in
       the  kernel source.  This information is taken directly from that file.

	      Sets the bit mask 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  mother
	      boards)  mess up the keyboard when accessing units 2 or 3.  This
	      option is somewhat obsoleted by the cmos option.

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

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

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

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

	      Tells the floppy driver that you	have  only  floppy  controller

       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.

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

	      Tells the floppy driver that you dont have a Thinkpad.

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

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

       floppy=no_unexpected_interrupts or floppy=L40SX
	      Dont 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

   The Sound Driver
       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 kernel source file  Documentation/sound/oss/README.OSS
       (drivers/sound/Readme.linux  in	older  kernel versions).  It accepts a
       boot arg of the form:


	      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,

	      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.

   ISDN Drivers
       The ICN ISDN driver


	      where icn_id1,icn_id2 are two strings used to identify the  card
	      in kernel messages.

       The PCBIT ISDN driver


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

       The Teles ISDN driver


	      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

   Serial Port Drivers
       The RISCom/8 Multiport Serial Driver (riscom8=)


	      More  details  can   be	found	in   /usr/src/linux/Documenta

       The DigiBoard Driver (digi=)
	      If this option is used, it should have precisely six parameters.


	      The parameters maybe given  as  integers,  or  as  strings.   If
	      strings  are  used,  then  iobase and membase should be given in
	      hexadecimal.  The integer arguments (fewer may be given) are  in
	      order:   status	(Enable(1)  or	Disable(0)  this  card),  type
	      (PC/Xi(0), PC/Xe(1), PC/Xeve(2), PC/Xem(3)),  altpin  (Enable(1)
	      or  Disable(0)  alternate  pin arrangement), numports (number of
	      ports on this card), iobase (I/O Port where card	is  configured
	      (in  HEX)), membase (base of memory window (in HEX)).  Thus, the
	      following two boot prompt arguments are equivalent:


	      More details can be found in  /usr/src/linux/Documentation/digi

       The Baycom Serial/Parallel Radio Modem


	      There  are  precisely 3 parameters; for several cards, give sev
	      eral baycom= commands.  The modem parameter is a	string	that
	      can  take  one of the values ser12, ser12*, par96, par96*.  Here
	      the * denotes that software DCD is to be used,  and  ser12/par96
	      chooses  between	the  supported modem types.  For more details,
	      see    the    file    Documentation/networking/baycom.txt    (or
	      drivers/net/README.baycom  for  older  kernels)  in  the	kernel

       Soundcard radio modem driver


	      All parameters except the last are  integers;  the  dummy  0  is
	      required because of a bug in the setup code.  The mode parameter
	      is a string with syntax hw:modem, where hw is one of  sbc,  wss,
	      wssfdx and modem is one of afsk1200, fsk9600.

   The Line Printer Driver
       lp=  Syntax:


	      You can tell the printer driver what ports to use and what ports
	      not to use.  The latter comes in handy if  you  dont  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 port names.  For example,
	      lp=none,parport0	would use the first parallel port for lp1, and
	      disable lp0.  To disable the printer driver  entirely,  one  can
	      use lp=0.

       WDT500/501 driver


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

	      And precisely the same is true for the msmouse driver.

       ATARI mouse setup


	      If only one argument is given, it is used for  both  x-threshold
	      and y-threshold.	Otherwise, the first argument is the x-thresh
	      old, and the second the  y-threshold.   These  values  must  lie
	      between 1 and 20 (inclusive); the default is 2.

   Video Hardware
	      This  option tells the console driver not to use hardware scroll
	      (where a scroll is effected by moving the screen origin in video
	      memory,  instead of moving the data).  It is required by certain
	      Braille machines.

       lilo.conf(5), klogd(8), lilo(8), mount(8), rdev(8)

       Large parts of this man page have been derived from the Boot  Parameter
       HOWTO  (version 1.0.1) written by Paul Gortmaker.  More information may
       be found in this (or a more recent) HOWTO.   An	up-to-date  source  of
       information is /usr/src/linux/Documentation/kernel-parameters.txt.

       This  page  is  part of release 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2007-12-16			  BOOTPARAM(7)

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