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BOOTPARAM(7)		   Linux Programmer's 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 a boot loader that is able to  pass
       parameters, such as GRUB.

   The argument list
       The  kernel  command  line is parsed into a list of strings (boot argu‐
       ments) separated by spaces.  Most of the boot arguments take  have  the


       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 handles only 10 comma sepa‐
       rated parameters per keyword.  (However, you can reuse the same keyword
       with  up to an additional 10 parameters in unusually complicated situa‐
       tions, assuming the setup function supports it.)

       Most of the sorting is coded in the  kernel  source  file  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(1) program.  The most common argument
       that is passed to the init process is the word 'single' which instructs
       it  to  boot  the  computer in single user mode, and not launch all the
       usual daemons.  Check the  manual  page	for  the  version  of  init(1)
       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 argument causes Linux to ignore the maths coproces‐
	      sor 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  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.

	      This  argument tells the kernel what device is to be used as the
	      root filesystem 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 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  num‐
	      ber,  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 filesystem.  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.)

	      The 'rootfstype' option tells  the  kernel  to  mount  the  root
	      filesystem  as  if  it where of the type specified.  This can be
	      useful (for example) to mount an ext3  filesystem	 as  ext2  and
	      then  remove the journal in the root filesystem, in fact revert‐
	      ing its format from ext3 to ext2 without the need	 to  boot  the
	      box from alternate media.

       'ro' and 'rw'
	      The 'ro' option tells the kernel to mount the root filesystem as
	      'read-only' so that filesystem consistency check programs (fsck)
	      can  do  their work on a quiescent filesystem.  No processes can
	      write to files  on  the  filesystem  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  filesystem
	      read/write.  This is the default.

	      This  tells  the kernel the location of the suspend-to-disk data
	      that you want the machine	 to  resume  from  after  hibernation.
	      Usually, it is the same as your swap partition or file. Example:


	      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 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.

	      The BIOS call defined in the PC specification that  returns  the
	      amount  of  installed  memory  was  designed  only 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 argument to  tell	 Linux
	      how  much memory you have.  The value is in decimal or hexadeci‐
	      mal (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:  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
	      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
	      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).

	      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
	      nonzero value.  This is done either by specifying CONFIG_PROFILE
	      at  compile  time,  or by giving the 'profile=' option.  Now the
	      value that prof_shift gets will be N, when given, or CONFIG_PRO‐
	      FILE_SHIFT, when that is given, or 2, the default.  The signifi‐
	      cance 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.

	      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 filesystem 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.)  These days ram disks use the  buffer  cache,  and  grow
       dynamically.   For  a  lot  of  information in conjunction with the new
       ramdisk	setup,	see  the  kernel  source   file	  Documentation/block‐
       dev/ramdisk.txt (Documentation/ramdisk.txt in older kernels).

       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;
	      afterward	 the "real" root filesystem is mounted, and the initrd
	      filesystem 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 kernel
	      source file 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, and
       so on.

       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 'subdevices' 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/ for older kernels) in the Linux ker‐
	      nel 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 argument 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 nonzero 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  argument
	      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 nonzero, indicates that extended transla‐
	      tion for	large  disks  is  enabled.   The  no_reset  value,  if
	      nonzero, 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 used only 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 the kernel source file	drivers/scsi/BusLogic.c.   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


       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 the kernel source file

       NCR5380 and NCR53C400 configuration
	      The boot argument is of the form




	      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 Linux 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 the
	      kernel source file drivers/scsi/ncr53c8xx.c.

       NCR53c406a configuration


	      Specify irq = 0 for noninterrupt 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 argument 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 argument 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 the kernel source file

   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 Linux 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 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 expects
	      only three values (C/H/S); any more or  any  less	 and  it  will
	      silently	ignore	you.   Also, it accepts only '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 argument 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.	 Don't disappoint  it.
	      Here  is	an example usage for a WD1002 controller with the BIOS
	      disabled/removed, using the 'default' XT controller parameters:


       Syquest's EZ* removable disks


   IBM MCA bus devices
       See also the kernel source file 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	 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:


	      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:


	      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 nonnumeric 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 probe only for one.  This can be accom‐
       plished 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 Linux kernel source.	 This information is taken directly from  that

	      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  nonstandard  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 don't 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 nonstandard CMOS types.  Setting
	      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
	      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

   The sound driver
       The sound driver can also accept boot arguments to  override  the  com‐
       piled in values.	 This is not recommended, as it is rather complex.  It
       is   described	in   the   Linux   kernel   source   file   Documenta‐
       tion/sound/oss/README.OSS  (drivers/sound/Readme.linux  in older kernel
       versions).  It accepts a boot argument 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  argument  of  'sound=0'  will  disable  the	 sound	driver

   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 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


	      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 the kernel source file 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 the kernel source file Documenta‐

       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	 driv‐
	      ers/net/README.baycom for older kernels)	in  the	 Linux	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,
	      or wssfdx, and modem is one of afsk1200 or fsk9600.

   The line printer driver


	      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


   Mouse drivers
	      The busmouse driver accepts only 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.

       klogd(8), mount(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  the  kernel  source  file  Documentation/kernel-parame‐

       This  page  is  part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

Linux				  2013-08-01			  BOOTPARAM(7)

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