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BOOTPARAM(7)		   Linux Programmer's Manual		  BOOTPARAM(7)

NAME
       bootparam - Introduction to boot time parameters of the Linux kernel

DESCRIPTION
       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
       details.

       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:

	      name[=value_1][,value_2]...[,value_10]

       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‐
       ment.

       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
       'init=...'
	      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.

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

       'nfsroot=...'
	      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.

       'no387'
	      (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!

       'no-hlt'
	      (Only  when  CONFIG_BUGi386  is  defined.)   Some	 of  the early
	      i486DX-100 chips have a problem with the 'hlt'  instruction,  in
	      that  they  can't	 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.

       'root=...'
	      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‐
	      tional.

	      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).

       'reserve=...'
	      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 hardware that reacts badly to the prob‐
	      ing, or hardware that would be mistakenly identified, or	merely
	      hardware you don't want the kernel to initialize.

	      The reserve boot-time argument specifies an I/O port region that
	      shouldn't 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.

       'mem=...'
	      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.

       'panic=N'
	      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".

       'reboot=[warm|cold][,[bios|hard]]'
	      (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
	      doesn't  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
       'debug'
	      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 <linux/kernel.h>.)  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).

       'profile=N'
	      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	you'll	want  to  use  a tool such as readprofile.c to
	      digest it.  Writing to /proc/profile will clear the counters.

       'swap=N1,N2,N3,N4,N5,N6,N7,N8'
	      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.

       'buff=N1,N2,N3,N4,N5,N6'
	      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 buf‐
       fer  cache,  and grow dynamically.  For a lot of information (e.g., how
       to use  rdev(8)	in  conjunction	 with  the  new	 ramdisk  setup),  see
       /usr/src/linux/Documentation/ramdisk.txt.

       There are four parameters, two boolean and two integral.

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

       'prompt_ramdisk=N'
	      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).

       'ramdisk_start=N'
	      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.

       'noinitrd'
	      (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
	      /usr/src/linux/Documentation/initrd.txt.

	      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,
       etc.

       scsi-id -- the ID that the host adapter uses to identify itself on  the
       SCSI  bus.   Only some host adapters allow you to change this value, as
       most have it permanently specified internally.  The usual default value
       is 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.

       'max_scsi_luns=...'
	      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:

	      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 file  Documentation/scsi/st.txt
	      (or  drivers/scsi/README.st  for	older  kernels)	 in the kernel
	      source.

       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:

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

	      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.

       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.

	      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.	 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.

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

	      aic7xxx=extended,no_reset

	      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.

       AM53C974

	      AM53C974=host-scsi-id,target-scsi-id,max-rate,max-offset

       BusLogic SCSI Hosts configuration ('BusLogic=')

	      BusLogic=N1,N2,N3,N4,N5,S1,S2,...

	      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:<Per-Target-Spec>),
	      over  Error  Recovery (ER:Default, ER:HardReset, ER:BusDeviceRe‐
	      set, ER:None, ER:<Per-Target-Spec>), 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

	      eata=iobase,iobase,....

       Future Domain TMC-16x0 configuration

	      fdomain=iobase,irq[,adapter_id]

       Great Valley Products (GVP) SCSI controller configuration

	      gvp11=dma_transfer_bitmask

       Future Domain TMC-8xx, TMC-950 configuration

	      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.

       IN2000 configuration

	      in2000=S

	      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  /usr/src/linux/driv‐
	      ers/scsi/in2000.c.

       NCR5380 and NCR53C400 configuration
	      The boot arg is of the form

	      ncr5380=iobase,irq,dma

	      or

	      ncr53c400=iobase,irq

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

       NCR53C8xx configuration

	      ncr53c8xx=S

	      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
	      /usr/src/linux/drivers/scsi/ncr53c8xx.c.

       NCR53c406a configuration

	      ncr53c406a=iobase[,irq[,fastpio]]

	      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:

	      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.

       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:

	      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.

       Trantor T128 configuration
	      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.

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

	      eata=iobase,iobase,....

       WD7000 configuration

	      wd7000=irq,dma,iobase

       Commodore Amiga A2091/590 SCSI controller configuration

	      wd33c93=S

	      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  /usr/src/linux/driv‐
	      ers/scsi/wd33c93.c.

   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
	      expected.

	      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
	      modes.

       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
	      usable.

       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  isn't  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:

	      hd=cyls,heads,sects

	      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:

	      xd=type,irq,iobase,dma_chan

	      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.  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

       Syquest's EZ* removable disks

	      ez=iobase[,irq[,rep[,nybble]]]

   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:

	      ed=cyls,heads,sectors.

	      For a ThinkPad-720, add the option

	      tp720=1.

       IBM Microchannel SCSI Subsystem configuration

	      ibmmcascsi=N

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

       The Aztech Interface
	      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.

       Parallel port CD-ROM drives
	      Syntax:

	      pcd.driveN=prt,pro,uni,mod,slv,dly
	      pcd.nice=nice

	      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 driver's 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:

	      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.

       The CDU-535 Sony Interface
	      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.

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

	      gscd=iobase

       The ISP16 CD-ROM Interface
	      Syntax:

	      isp16=[iobase[,irq[,dma[,type]]]]

	      (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:

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

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

	      mcdx=iobase[,irq]

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

	      optcd=iobase

       The Phillips CM206 Interface
	      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 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:

	      sjcd=iobase[,irq[,dma_channel]]

       The SoundBlaster Pro Interface
	      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.

   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:

	      ether=irq,iobase[,param_1[,...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 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:

	      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.

	      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.

       floppy=mask,allowed_drive_mask
	      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.

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

       floppy=daring
	      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
	      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 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.

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

       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.)

   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:

	      sound=device1[,device2[,device3...[,device10]]]

	      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.

   ISDN Drivers
       The ICN ISDN driver
	      Syntax:

	      icn=iobase,membase,icn_id1,icn_id2

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

       The PCBIT ISDN driver
	      Syntax:

	      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.

       The Teles ISDN driver
	      Syntax:

	      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.

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

	      riscom=iobase1[,iobase2[,iobase3[,iobase4]]]

	      More   details   can   be	  found	 in  /usr/src/linux/Documenta‐
	      tion/riscom8.txt.

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

	      digi=status,type,altpin,numports,iobase,membase

	      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:

	      digi=E,PC/Xi,D,16,200,D0000
	      digi=1,0,0,16,0x200,851968

	      More  details can be found in /usr/src/linux/Documentation/digi‐
	      board.txt.

       The Baycom Serial/Parallel Radio Modem
	      Syntax:

	      baycom=iobase,irq,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	 driv‐
	      ers/net/README.baycom for older kernels) in the kernel source.

       Soundcard radio modem driver
	      Syntax:

	      soundmodem=iobase,irq,dma[,dma2[,serio[,pario]]],0,mode

	      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:

	      lp=0
	      lp=auto
	      lp=reset
	      lp=port[,port...]

	      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 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
	      Syntax:

	      wdt=io,irq

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

       'msmouse=irq'
	      And precisely the same is true for the msmouse driver.

       ATARI mouse setup

	      atamouse=threshold[,y-threshold]

	      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
       'no-scroll'
	      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.

SEE ALSO
       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.

COLOPHON
       This  page  is  part of release 3.23 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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