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 gen-
     eral 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  parame-
     ters.   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  Almes-
     berger 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

     The other commonly used Linux loader is `LoadLin' which is a
     DOS program that has the capability to launch a Linux kernel
     from the DOS prompt (with boot-args) assuming  that  certain
     resources  are available.  This is good for people that 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 loading
     Linux from the DOS prompt with loadlin avoids the  reset  of
     the card that happens if one rebooted instead.


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


     where `name' is a unique keyword that is  used  to  identify
     what  part  of the kernel the associated values (if any) are
     to be given to.  Note the  limit  of  10  is  real,  as  the
     present  code only handles 10 comma separated parameters per
     keyword. (However, you can re-use the same keyword  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 spe-
     cial 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 ker-
     nel. 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 argu-
     ments 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  funtion  as described above is then interpreted as an
     environment variable to be set. A (useless?)  example  would
     be to use `TERM=vt100' as a boot argument.

     Any remaining arguments that were not picked up by the  ker-
     nel  and  were  not interpreted as environment variables are
     then passed onto process one, which is usually the init pro-
     gram.  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.


     This sets the initial command to be executed by the  kernel.
     If  this is not set, or cannot be found, the kernel will try
     /etc/init, then /bin/init, then /sbin/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  coproces-
     sor  chips  have  bugs that show up when used in 32 bit pro-
     tected 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

     (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 noth-
     ing  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 set-
     ting 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  numeri-
     cally.   A  symbolic  specification  has the form /dev/XXYN,
     where XX designates the device type (`hd' for ST-506  compa-
     tible 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 conventional.

     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  filesys-
     tem  as `readonly' so that filesystem consistency check pro-
     grams (fsck) can do their work on a quiescent  file  system.
     No  processes  can write to files on the filesystem in ques-
     tion until it is `remounted' as read/write capable, e.g., by
     `mount -w -n -o remount /'.  (See also mount(8).)

     The `rw' option tells the kernel to mount the root  filesys-
     tem read/write.  This is the default.

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

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


     In some machines it  may  be  necessary  to  prevent  device
     drivers  from  checking  for  devices  (auto-probing)  in  a
     specific region. This may be because of hardware that reacts
     badly  to  the probing, or hardware that would be mistakenly
     identified, or merely hardware you don't want the kernel  to

     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 only designed 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  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  cacheing  or  whatever, so you might not actually
     have up to the full 96MB addressable.  The reverse  is  also
     true:  some  chipsets  will  map the physical memory that is
     covered by the BIOS area into the area just past the top  of
     memory, so the top-of-mem might actually be 96MB + 384kB for
     example.  If you tell linux that it has more memory than  it
     actually  does  have,  bad  things will happen: maybe not at
     once, but surely eventually.''

     By default the kernel will not reboot  after  a  panic,  but
     this option will cause a kernel reboot after N seconds (if N
     > 0).  This panic timeout can also  be  set  by  "echo  N  >

     (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.


     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 con-
     sole.  (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 speci-
     fying CONFIG_PROFILE at compile time, or by giving the `pro-
     file='  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 incre-

          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  con-
     trol 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  manage-
     ment. For kernel tuners only.


     (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 flop-
     pies) 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, or by use of
     rdev(8).)  These days ram disks use the  buffer  cache,  and
     grow  dynamically.   For  a lot of information (e.g., how to
     use rdev(8) in conjunction with the new ramdisk setup),  see

     There are four parameters, two boolean and two integral.

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

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

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

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

     (Only if the kernel was compiled with CONFIG_BLK_DEV_RAM and
     CONFIG_BLK_DEV_INITRD.)   These  days it is possible to com-
     pile the  kernel  to  use  initrd.   When  this  feature  is
     enabled,  the  boot process will load the kernel and an ini-
     tial ramdisk; then the kernel converts initrd into  a  "nor-
     mal"  ramdisk,  which  is mounted read-write as root device;
     then /linuxrc is executed; afterwards the "real"  root  file
     system  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 `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


     General notation for this section:

     iobase -- the first I/O port that the  SCSI  host  occupies.
     These are specified in hexidecimal notation, and usually lie
     in the range from 0x200 to 0x3ff.

     irq -- the hardware interrupt that the card is configured to
     use.   Valid  values  will be dependent on the card in ques-
     tion, but will usually be 5, 7, 9, 10, 11, 12, and  15.  The
     other  values  are  usually used for common peripherals like
     IDE hard disks, floppies, serial ports, etc.

     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  behaviour  as  a
     boot argument.

     A SCSI device can have a number of  `sub-devices'  contained
     within  itself.  The  most  common example is one of the new
     SCSI CD-ROMs that handle more than one disk at a time.  Each
     CD  is  addressed  as  a `Logical Unit Number' (LUN) of that
     particular device. But most devices,  such  as  hard  disks,
     tape  drives  and  such  are  only  one  device, and will be
     assigned to LUN zero.

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

     To specify the number of probed LUNs  at  boot,  one  enters
     `max_scsi_luns=n' as a boot arg, where n is a number between
     one and eight. To avoid problems  as  described  above,  one
     would use n=1 to avoid upsetting such broken devices.

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


     The first two numbers are specified in  units  of  kB.   The
     default  buf_size  is 32kB, and the maximum size that can be
     specified is a ridiculous 16384kB.  The  write_threshold  is
     the  value  at which the buffer is committed to tape, with a
     default value of 30kB.  The maximum number of buffers varies
     with  the  number  of  drives detected, and has a default of
     two.  An example usage would be:


     Full details can be found in the file that  is  in
     the scsi directory of the kernel source tree.

  Adaptec aha151x, aha152x, aic6260,  aic6360,  SB16-SCSI  confi-
     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 arg of the form:


     If the driver was compiled with debugging enabled,  a  sixth
     value can be specified to set the debug level.

     All the parameters are as described at the top of this  sec-
     tion,   and   the   reconnect   value   will   allow  device
     disconnect/reconnect if a non-zero value is used. An example
     usage is as follows:


     Note that the parameters must be specified in order, meaning
     that  if you want to specify a parity setting, then you will
     have to specify an iobase, irq, scsi-id and reconnect  value
     as well.

  Adaptec aha154x configuration
     The aha1542 series cards have an  i82077  floppy  controller
     onboard,  while  the  aha1540 series cards do not. These are
     busmastering cards, and have parameters to set  the  ``fair-
     ness'' that is used to share the bus with other devices. The
     boot arg looks like the following.


     Valid iobase values are usually one of: 0x130, 0x134, 0x230,
     0x234, 0x330, 0x334.  Clone cards may permit other values.

     The buson, busoff values refer to the number of microseconds
     that  the  card dominates the ISA bus. The defaults are 11us
     on, and 4us off, so that other cards (such as an  ISA  LANCE
     Ethernet card) have a chance to get access to the ISA bus.

     The dmaspeed value refers to the rate (in MB/s) at which the
     DMA (Direct Memory Access) transfers proceed. The default is
     5MB/s.  Newer revision cards allow you to select this  value
     as  part of the soft-configuration, older cards use jumpers.
     You can use values up to 10MB/s assuming that  your  mother-
     board 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:


     The extended value, if  non-zero,  indicates  that  extended
     translation  for large disks is enabled. The no_reset value,
     if non-zero, tells the driver not to reset the SCSI bus when
     setting up the host adaptor at boot.

  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 only used for probing ISA and VLB cards.  In
     addition, if the driver has  been  compiled  with  debugging
     enabled,  the level of debugging output can be set by adding
     an 0xdeb[0-f] parameter. The 0-f allows setting the level of
     the debugging messages to any of 16 levels of verbosity.


  BusLogic SCSI Hosts configuration (`BusLogic=')

     For an extensive discussion of  the  BusLogic  command  line
     parameters,    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 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

     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 /usr/src/linux/drivers/scsi/in2000.c.

  NCR5380 and NCR53C400 configuration
     The boot arg 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

  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

  NCR53c406a configuration

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

  IOMEGA PPA3 configuration

     Here iobase is the parallel port  address  (default  0x378),
     speed_high  is  the port delay in data phase in microseconds
     (default 1), speed_low is the port delay  (in  microseconds)
     otherwise (default 6), and nybble is a boolean `force nybble
     (4-bit)    mode'    (default     0=false).      See     also

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


     The only difference is that you can specify an IRQ value  of
     255, which will tell the driver to work without using inter-
     rupts, albeit at a performance loss. The iobase  is  usually

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


     The mem_base value is the value of  the  memory  mapped  I/O
     region  that  the card uses. This will usually be one of the
     following  values:   0xc8000,  0xca000,  0xcc000,   0xce000,
     0xdc000, 0xde000.

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


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

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


  WD7000 configuration

  Commodore Amiga A2091/590 SCSI controller configuration

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


  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
     unspecified drive in the (a, ..., h) sequence.  For the fol-
     lowing discussions, the `hd=' option will be cited for brev-
     ity. See the file README.ide in linux/drivers/block for more

  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  inter-
     face  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

  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 opera-
     tions 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 useable.

  The `hd=nowerr' option
     Some drives apparently have the WRERR_STAT bit stuck on per-
     manently.   This enables a work-around for these broken dev-

  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 argument, i.e. `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 recognised, you will have  to
     use a boot arg of the form:


     The type value specifies the particular manufacturer of  the
     card,  and  are  as follows: 0=generic; 1=DTC; 2,3,4=Western
     Digital, 5,6,7=Seagate; 8=OMTI. The only difference  between
     multiple types from the same manufacturer is the BIOS string
     used for detection, which is not used if the type is  speci-

     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


  Syquest's EZ* removable disks


     See also /usr/src/linux/Documentation/mca.txt.

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


     For a ThinkPad-720, add the option


  IBM Microchannel SCSI Subsystem configuration

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


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


     If you set the magic_number to 0x79 then the driver will try
     and  run anyway in the event of an unknown firmware version.
     All other values are ignored.

  The MicroSolutions `backpack' CDrom


  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 peo-
     ple 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:


  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 por-
     tion of the card.


     Different drivers make use of different parameters, but they
     all  at  least  share having an IRQ, an I/O port base value,
     and a name. In its most generic  form,  it  looks  something
     like this:


     The first non-numeric argument is taken as  the  name.   The
     param_n  values (if applicable) usually have different mean-
     ings for each different card/driver.  Typical param_n values
     are  used  to  specify  things  like  shared memory address,
     interface selection, DMA channel and the like.

     The most common use of this parameter is  to  force  probing
     for  a second ethercard, as the default is to only probe for
     one. This can be accomplished with a simple:


     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 mul-
     tiple  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


     There are many floppy  driver  options,  and  they  are  all
     listed in README.fd in linux/drivers/block. This information
     is taken directly from that file.

     Sets the bitmask of allowed drives to mask. By default, only
     units 0 and 1 of each floppy controller are allowed. This is
     done because certain non-standard hardware (ASUS PCI mother-
     boards)  mess  up  the keyboard when accessing units 2 or 3.
     This option is somewhat obsoleted by the cmos option.

     Sets the bitmask of allowed drives to all drives.  Use  this
     if  you have more than two drives connected to a floppy con-

     Sets the bitmask 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 opera-
     tion, but may fail on certain controllers. This may speed up
     certain operations.

     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  controll-
     ers.  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 bitmask. This is useful if you have
     more than two floppy drives (only two can  be  described  in
     the  physical  cmos), or if your BIOS uses non-standard CMOS
     types.  Setting the CMOS to  0  for  the  first  two  drives
     (default) makes the floppy driver read the physical cmos for
     those drives.

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

  floppy=no_unexpected_interrupts or floppy=L40SX
     Don't print  a  message  when  an  unexpected  interrupt  is
     received.  This  is  needed  on IBM L40SX laptops in certain
     video modes. (There seems to be an interaction between video
     and  floppy.  The  unexpected interrupts only affect perfor-
     mance, and can safely be ignored.)


     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  Readme.Linux  file,  in
     linux/drivers/sound. It accepts a boot arg of the form:


     where each deviceN value is of the following format 0xTaaaId
     and the bytes are used as follows:

     T - device type: 1=FM, 2=SB, 3=PAS, 4=GUS, 5=MPU401, 6=SB16,

     aaa - I/O address in hex.

     I - interrupt line in hex (i.e 10=a, 11=b, ...)

     d - DMA channel.

     As you can see it gets pretty messy, and you are better  off
     to compile in your own personal values as recommended. Using
     a boot arg  of  `sound=0'  will  disable  the  sound  driver


  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 identifier.


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


     More       details       can       be        found        in

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


     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), num-
     ports (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 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

  Soundcard radio modem driver


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


     As of kernels newer than 1.3.75, you can  tell  the  printer
     driver  what  ports  to  use  and what ports not to use. The
     latter comes in handy if you don't want the  printer  driver
     to claim all available parallel ports, so that other drivers
     (e.g. PLIP, PPA) can use them instead.
     The format of the argument is multiple i/o, IRQ  pairs.  For
     example,  lp=0x3bc,0,0x378,7  would use the port at 0x3bc in
     IRQ-less (polling) mode, and use  IRQ  7  for  the  port  at
     0x378. The port at 0x278 (if any) would not be probed, since
     autoprobing only takes place in the absence of a `lp=' argu-
     ment.  To  disable  the printer driver entirely, one can use

  WDT500/501 driver



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

     And precisely the same is true for the msmouse driver.

  ATARI mouse setup

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


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


     Linus Torvalds (and many others)


     klogd(8), lilo.conf(5), 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.
     Slightly more information may be found in this  (or  a  more
     recent) HOWTO.