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       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
       arguments) separated by spaces.  Most of the boot arguments  take  have
       the form:


       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
       separated parameters per keyword.  (However, you  can  reuse  the  same
       keyword with up to an additional 10 parameters in unusually complicated
       situations, 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

       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
              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  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
              designates 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  filesystem.   The  '/dev/'  part  is   purely

              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
              reverting 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
              probing,  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
              probing 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
              determine  how  much memory is installed.  If you have more than
              64MB of RAM installed, you can use this boot  argument  to  tell
              Linux  how  much  memory  you  have.  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
                   horribly sooner or  later.   The  parameter  indicates  the
                   highest  addressable  RAM address, so 'mem=0x1000000' means
                   you have 16MB of memory, for example.  For a  96MB  machine
                   this would be 'mem=0x6000000'.

                   NOTE:  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_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.

              Set   the   eight   parameters    max_page_age,    page_advance,
              page_decline,        page_initial_age,        age_cluster_fract,
              age_cluster_min, pageout_weight, bufferout_weight  that  control
              the kernel 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
       contents  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'
       parameter  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/blockdev/ramdisk.txt  (Documentation/ramdisk.txt in older

       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
              compiled 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
       usually  be  5, 7, 9, 10, 11, 12, and 15.  The other values are usually
       used for common peripherals  like  IDE  hard  disks,  floppies,  serial
       ports, 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
       checking.   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
              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
              Soundblaster-16 SCSI.

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


              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
              busmastering cards, and have parameters to  set  the  "fairness"
              that  is  used  to  share  the bus with other devices.  The boot
              argument looks like the following.


              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
              translation  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
              values  (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
              parameters,  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
              seconds.  This is the amount of time  to  wait  between  a  Host
              Adapter  Hard Reset which initiates a SCSI Bus Reset and issuing
              any SCSI Commands.  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
              Queuing  (TQ:Default,  TQ:Enable,  TQ:Disable,   TQ:<Per-Target-
              Spec>),   over   Error   Recovery   (ER:Default,   ER:HardReset,
              ER:BusDeviceReset, ER:None, ER:<Per-Target-Spec>), and over Host
              Adapter Probing (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
              Documentation/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_parity), 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
              unspecified  drive  in  the  (a,  ...,  h)  sequence.   For  the
              following discussions,  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
              cylinder/head/sectors  values  will be those used by fdisk.  The
              write precompensation value is ignored for IDE disks.   The  IRQ
              value  specified will be the IRQ used for the interface that the
              drive resides on, and is not really a drive-specific parameter.

       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
              permanently.   This  enables  a  work-around  for  these  broken

       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
              argument, 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
              syntax 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
              recognized  types  are:   'Sanyo",   'Sony',   'Panasonic'   and

       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
              specify 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
       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
       Documentation/floppy.txt (or drivers/block/README.fd for older kernels)
       in  the  Linux  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   nonstandard   hardware   (ASUS    PCI
              motherboards)  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
              controller.  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
              physical 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
       compiled in values.  This is not recommended, as it is rather  complex.
       It    is    described    in    the    Linux    kernel    source    file
       Documentation/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

       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

       The Baycom Serial/Parallel Radio Modem


              There  are  precisely  3  parameters;  for  several  cards, give
              several '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 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-
              threshold, 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-


       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

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