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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  software  that  is  able  to  pass
       parameters,  like  LILO  or loadlin.  For a few parameters one can also
       modify the kernel image itself, using rdev,  see  rdev(8)  for  further

       The  LILO  program  (LInux LOader) written by Werner Almesberger is the
       most commonly used.  It has the ability to boot  various  kernels,  and
       stores  the  configuration  information  in  a  plain  text file.  (See
       lilo(8) and lilo.conf(5).)  LILO can boot DOS,  OS/2,  Linux,  FreeBSD,
       UnixWare, etc., and is quite flexible.

       The  other  commonly  used  Linux  loader  is  'LoadLin' which is a DOS
       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 Argument List
       The kernel command  line  is  parsed  into  a  list  of  strings  (boot
       arguments)  separated  by  spaces.  Most of the boot args take 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  only  handles  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 goes on in linux/init/main.c.  First, the kernel
       checks to see if the argument is any of the special arguments  'root=',
       'nfsroot=', 'nfsaddrs=', 'ro', 'rw', 'debug' or 'init'.  The meaning of
       these special arguments is described below.

       Then it walks a list of setup functions (contained  in  the  bootsetups
       array) to see if the specified argument string (such as 'foo') has been
       associated with a  setup  function  ('foo_setup()')  for  a  particular
       device  or  part  of  the  kernel.   If  you passed the kernel the line
       foo=3,4,5,6 then the kernel would search the bootsetups array to see if
       'foo' was registered.  If it was, then it would call the setup function
       associated with 'foo' (foo_setup()) and hand it the arguments 3,  4,  5
       and 6 as given on the kernel command line.

       Anything of the form 'foo=bar' that is not accepted as a setup function
       as described above is then interpreted as an environment variable to be
       set.   A  (useless?)  example  would  be  to use 'TERM=vt100' as a boot

       Any remaining arguments that were not picked up by the kernel and  were
       not  interpreted  as environment variables are then passed onto process
       one, which is usually the init program.  The most common argument  that
       is passed to the init process is the word 'single' which instructs init
       to boot the computer in single user mode, and not launch all the  usual
       daemons.   Check  the  manual page for the version of init installed on
       your system to see what arguments it accepts.

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

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

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

              (Only when CONFIG_BUGi386 is defined.)   Some  i387  coprocessor
              chips have bugs that show up when used in 32 bit protected mode.
              For example, some of the early ULSI-387 chips would cause  solid
              lockups while performing floating-point calculations.  Using the
              'no387' boot arg causes Linux to ignore  the  maths  coprocessor
              even  if you have one.  Of course you must then have your kernel
              compiled with math emulation support!

              (Only when  CONFIG_BUGi386  is  defined.)   Some  of  the  early
              i486DX-100  chips  have a problem with the 'hlt' instruction, in
              that they 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  file system while booting.  The default of this setting is
              determined at compile time, and usually is the value of the root
              device  of the system that the kernel was built on.  To override
              this value, and select the  second  floppy  drive  as  the  root
              device,  one  would  use  'root=/dev/fd1'.  (The root device can
              also be set using rdev(8).)

              The root device can be specified symbolically or numerically.  A
              symbolic   specification   has  the  form  /dev/XXYN,  where  XX
              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  file  system.   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.)

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

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

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

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


              In some machines it may be necessary to prevent  device  drivers
              from  checking  for devices (auto-probing) in a specific region.
              This may be  because  of  hardware  that  reacts  badly  to  the
              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  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
                   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  file system or hardware) must be loaded before the
       main disk can be accessed.

       In Linux 1.3.48, ramdisk handling was  changed  drastically.   Earlier,
       the  memory  was  allocated  statically,  and  there  was a 'ramdisk=N'
       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 /usr/src/linux/Documentation/ramdisk.txt.

       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 file system is mounted, and the initrd
              file  system  is  moved  over to /initrd; finally the usual boot
              sequence (e.g., invocation of /sbin/init) is performed.

              For  a  detailed  description  of  the   initrd   feature,   see

              The  'noinitrd'  option  tells  the  kernel that although it was
              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, 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
       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  kernel

       Adaptec aha151x, aha152x, aic6260, aic6360, SB16-SCSI configuration
              The  aha numbers refer to cards and the aic numbers refer to the
              actual  SCSI  chip  on  these  type  of  cards,  including   the
              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  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 arg
              looks like the following.


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

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

              The dmaspeed value refers to the rate (in MB/s) at which the DMA
              (Direct Memory Access) transfers proceed.  The default is 5MB/s.
              Newer revision cards allow you to select this value as  part  of
              the  soft-configuration,  older  cards use jumpers.  You can use
              values up to 10MB/s assuming that your motherboard is capable of
              handling  it.   Experiment  with  caution  if  using values over

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


              The  extended  value,  if  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 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 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

       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
              Documentation/scsi/g_NCR5380.txt                             (or
              drivers/scsi/README.g_NCR5380 for older kernels) in  the  kernel

       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 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 arg is of the form:


              The only difference is that you can specify an IRQ value of 255,
              which will tell the driver to  work  without  using  interrupts,
              albeit at a performance loss.  The iobase is usually 0x388.

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


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

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


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

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


       WD7000 configuration


       Commodore Amiga A2091/590 SCSI controller configuration


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

   Hard Disks
       IDE Disk/CD-ROM Driver Parameters
              The  IDE driver accepts a number of parameters, which range from
              disk geometry specifications, to support for  broken  controller
              chips.   Drive-specific  options  are  specified by using 'hdX='
              with X in 'a'-'h'.

              Non-drive-specific options are specified with the prefix  'hd='.
              Note that using a drive-specific prefix for a non-drive-specific
              option will still work, and the option will just be  applied  as

              Also  note  that  'hd='  can  be  used  to  refer  to  the  next
              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 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  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,  that  is,  'hda='  and so on are not valid here.  The
              format is as follows:


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

       XT Disk Driver Options ('xd=')
              If you are unfortunate enough to be using one of these old 8 bit
              cards that move data at a whopping  125kB/s  then  here  is  the
              scoop.   If  the  card is not recognized, you will have to use a
              boot arg of the form:


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

              The xd_setup() function does no  checking  on  the  values,  and
              assumes  that you entered all four values.  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 /usr/src/linux/Documentation/mca.txt.

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


              For a ThinkPad-720, add the option


       IBM Microchannel SCSI Subsystem configuration


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

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


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

       Parallel port CD-ROM drives


              where  'port' is the base address, 'pro' is the protocol number,
              'uni' is the unit selector (for chained devices), 'mod'  is  the
              mode  (or -1 to choose the best automatically), 'slv' is 1 if it
              should be a slave, and 'dly' is a small integer for slowing down
              port  accesses.   The 'nice' parameter controls the 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 only probe for one.  This
              can be accomplished with a simple:


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

              The Ethernet-HowTo has extensive documentation on using multiple
              cards  and  on  the  card/driver-specific  implementation of the
              param_n values where used.  Interested readers should  refer  to
              the section in that document on their particular card.

   The Floppy Disk Driver
       There  are  many  floppy  driver  options,  and  they are all listed in
       Documentation/floppy.txt (or drivers/block/README.fd for older kernels)
       in  the  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
              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 args to override the compiled in
       values.  This is not recommended, as  it  is  rather  complex.   It  is
       described  in the kernel source file Documentation/sound/oss/README.OSS
       (drivers/sound/Readme.linux in older kernel versions).   It  accepts  a
       boot arg of the form:


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

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

              aaa - I/O address in hex.

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

              d - DMA channel.

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

   ISDN Drivers
       The ICN ISDN driver


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

       The PCBIT ISDN driver


              where membaseN is the shared memory base of the 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 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 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  kernel

       Soundcard radio modem driver


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

   The Line Printer Driver
       'lp='  Syntax:


              You can tell the printer driver what ports to use and what ports
              not  to  use.   The  latter comes in handy if you 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 only accepts one parameter, that  being  the
              hardware IRQ value to be used.

              And precisely the same is true for the msmouse driver.

       ATARI mouse setup


              If  only  one argument is given, it is used for both x-threshold
              and y-threshold.   Otherwise,  the  first  argument  is  the  x-
              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.


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

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


       This page is part of release 3.35 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at