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

       bootparam - Introduction to boot time parameters of the Linux kernel

       The  Linux  kernel accepts certain 'command-line options' or 'boot time
       parameters' at the moment it is started.  In general this  is  used  to
       supply  the  kernel with information about hardware parameters that the
       kernel would not be able to determine on its own, or to  avoid/override
       the values that the kernel would otherwise detect.

       When  the  kernel  is booted directly by the BIOS (say from a floppy to
       which you copied a kernel using 'cp  zImage  /dev/fd0'),  you  have  no
       opportunity  to specify any parameters.  So, in order to take advantage
       of this possibility you have to use  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 pro-
       gram that has the capability to launch a  Linux  kernel  from  the  DOS
       prompt  (with boot-args) assuming that certain resources are available.
       This is good for people that want to launch Linux from DOS.

       It is also very useful if you have certain hardware which relies on the
       supplied  DOS  driver to put the hardware into a known state.  A common
       example is 'SoundBlaster Compatible' sound cards that require  the  DOS
       driver  to  twiddle  a few mystical registers to put the card into a SB
       compatible mode.  Booting DOS with the supplied driver, and then  load-
       ing Linux from the DOS prompt with loadlin avoids the reset of the card
       that happens if one rebooted instead.

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


       where  'name' is a unique keyword that is used to identify what part of
       the kernel the associated values (if any) are to be given to.  Note the
       limit  of  10  is real, as the present code only handles 10 comma sepa-
       rated parameters per keyword.  (However, you can re-use the  same  key-
       word  with  up  to an additional 10 parameters in unusually complicated
       situations, assuming the setup function supports it.)

       Most of the sorting goes on in linux/init/main.c.   First,  the  kernel
       checks  to see if the argument is any of the special arguments 'root=',
       'nfsroot=', 'nfsaddrs=', 'ro', 'rw', 'debug' or 'init'.  The meaning of
       these special arguments is described below.

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

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

       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  desig-
              nates  the  device  type  ('hd' for ST-506 compatible hard disk,
              with Y in 'a'-'d'; 'sd' for SCSI  compatible  disk,  with  Y  in
              'a'-'e'; 'ad' for Atari ACSI disk, with Y in 'a'-'e', 'ez' for a
              Syquest EZ135 parallel port removable drive,  with  Y='a',  'xd'
              for  XT  compatible  disk,  with  Y  either 'a' or 'b'; 'fd' for
              floppy disk, with Y the floppy drive number -- fd0 would be  the
              DOS  'A:'  drive, and fd1 would be 'B:'), Y the driver letter or
              number, and N the number (in decimal) of the partition  on  this
              device  (absent  in the case of floppies).  Recent kernels allow
              many other types,  mostly  for  CD-ROMs:  nfs,  ram,  scd,  mcd,
              cdu535,  aztcd,  cm206cd,  gscd, sbpcd, sonycd, bpcd.  (The type
              nfs specifies a net boot; ram refers to a ram disk.)

              Note that this has nothing to do with the designation  of  these
              devices on your file system.  The '/dev/' part is purely conven-

              The more awkward and less portable numeric specification of  the
              above  possible  root  devices  in  major/minor  format  is also
              accepted.  (E.g., /dev/sda3 is major 8, minor 3,  so  you  could
              use 'root=0x803' as an alternative.)

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

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

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

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


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

              The reserve boot-time argument specifies an I/O port region that
              shouldn't be probed.  A device driver will not probe a  reserved
              region,  unless  another boot argument explicitly specifies that
              it do so.

              For example, the boot line

              reserve=0x300,32  blah=0x300

              keeps all device drivers except the driver for 'blah' from prob-
              ing 0x300-0x31f.

              The  BIOS  call defined in the PC specification that returns the
              amount of installed memory was  only  designed  to  be  able  to
              report  up to 64MB.  Linux uses this BIOS call at boot to deter-
              mine how much memory is installed.  If you have more  than  64MB
              of  RAM  installed,  you can use this boot arg to tell Linux how
              much memory you have.  The value is in  decimal  or  hexadecimal
              (prefix  0x),  and  the  suffixes 'k' (times 1024) or 'M' (times
              1048576) can be used.  Here is a quote from Linus  on  usage  of
              the 'mem=' parameter.

                   The  kernel will accept any 'mem=xx' parameter you give it,
                   and if it turns out that you lied to it, it will crash hor-
                   ribly sooner or later.  The parameter indicates the highest
                   addressable RAM address, so 'mem=0x1000000' means you  have
                   16MB of memory, for example.  For a 96MB machine this would
                   be 'mem=0x6000000'.

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

              You can also use the boot argument 'mem=nopentium' to turn off 4
              MB  page  tables  on  kernels configured for IA32 systems with a
              pentium or newer CPU.

              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
              non-zero value.  This is done either by  specifying  CONFIG_PRO-
              FILE  at  compile time, or by giving the 'profile=' option.  Now
              the value that prof_shift gets will be N, when  given,  or  CON-
              FIG_PROFILE_SHIFT,  when  that is given, or 2, the default.  The
              significance of this variable is that it gives  the  granularity
              of  the  profiling: each clock tick, if the system was executing
              kernel code, a counter is incremented:

              profile[address >> prof_shift]++;

              The raw profiling information can be  read  from  /proc/profile.
              Probably  you'll  want  to  use  a tool such as readprofile.c to
              digest it.  Writing to /proc/profile will clear the counters.

              Set   the   eight   parameters    max_page_age,    page_advance,
              page_decline,   page_initial_age,  age_cluster_fract,  age_clus-
              ter_min, pageout_weight, bufferout_weight that control the  ker-
              nel swap algorithm.  For kernel tuners only.

              Set the six parameters max_buff_age, buff_advance, buff_decline,
              buff_initial_age, bufferout_weight, buffermem_grace that control
              kernel buffer memory management.  For kernel tuners only.

   Boot Arguments for Ramdisk Use
       (Only  if the kernel was compiled with CONFIG_BLK_DEV_RAM.)  In general
       it is a bad idea to use a ramdisk under Linux -- the  system  will  use
       available  memory more efficiently itself.  But while booting (or while
       constructing boot floppies) it is often useful to load the floppy  con-
       tents into a ramdisk.  One might also have a system in which first some
       modules (for file system or hardware) must be loaded  before  the  main
       disk can be accessed.

       In  Linux  1.3.48,  ramdisk handling was changed drastically.  Earlier,
       the memory was allocated statically, and there was a 'ramdisk=N' param-
       eter  to tell its size.  (This could also be set in the kernel image at
       compile time, or by use of rdev(8).)  These days ram disks use the buf-
       fer  cache,  and grow dynamically.  For a lot of information (e.g., how
       to use  rdev(8)  in  conjunction  with  the  new  ramdisk  setup),  see

       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;
              afterwards  the "real" root file system is mounted, and the ini-
              trd file system is moved over to /initrd; finally the usual boot
              sequence (e.g., invocation of /sbin/init) is performed.

              For   a   detailed   description  of  the  initrd  feature,  see

              The 'noinitrd' option tells the kernel that although it was com-
              piled  for  operation  with initrd, it should not go through the
              above steps, but leave the initrd data under /dev/initrd.  (This
              device  can  be used only once: the data is freed as soon as the
              last process that used it has closed /dev/initrd.)

   Boot Arguments for SCSI Devices
       General notation for this section:

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

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

       scsi-id -- the ID that the host adapter uses to identify itself on  the
       SCSI  bus.   Only some host adapters allow you to change this value, as
       most have it permanently specified internally.  The usual default value
       is 7, but the Seagate and Future Domain TMC-950 boards use 6.

       parity -- whether the SCSI host adapter expects the attached devices to
       supply a parity value with all information exchanges.  Specifying a one
       indicates parity checking is enabled, and a zero disables parity check-
       ing.  Again, not all adapters will support selection of parity behavior
       as a boot argument.

              A  SCSI  device  can  have  a  number of '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  Documentation/scsi/st.txt
              (or  drivers/scsi/README.st  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 Sound-
              blaster-16 SCSI.

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


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

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


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

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


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

       AdvanSys SCSI Hosts configuration ('advansys=')
              The AdvanSys driver can accept up to  four  i/o  addresses  that
              will  be probed for an AdvanSys SCSI card.  Note that these val-
              ues (if used) do not effect EISA or  PCI  probing  in  any  way.
              They  are only used for probing ISA and VLB cards.  In addition,
              if the driver has been  compiled  with  debugging  enabled,  the
              level  of  debugging  output  can be set by adding an 0xdeb[0-f]
              parameter.  The 0-f allows setting the level  of  the  debugging
              messages to any of 16 levels of verbosity.



       BusLogic SCSI Hosts configuration ('BusLogic=')


              For an extensive discussion of the BusLogic command line parame-
              ters,    see    /usr/src/linux/drivers/scsi/BusLogic.c    (lines
              3149-3270  in  the  kernel  version  I am looking at).  The text
              below is a very much abbreviated extract.

              The parameters N1-N5 are integers.  The  parameters  S1,...  are
              strings.   N1  is  the  I/O Address at which the Host Adapter is
              located.  N2 is the Tagged Queue Depth to use for Target Devices
              that  support Tagged Queuing.  N3 is the Bus Settle Time in sec-
              onds.  This is the amount of time to wait between a Host Adapter
              Hard Reset which initiates a SCSI Bus Reset and issuing any SCSI
              Commands.  N4 is the Local Options (for one Host  Adapter).   N5
              is the Global Options (for all Host Adapters).

              The string options are used to provide control over Tagged Queu-
              ing (TQ:Default, TQ:Enable,  TQ:Disable,  TQ:<Per-Target-Spec>),
              over  Error  Recovery (ER:Default, ER:HardReset, ER:BusDeviceRe-
              set, ER:None, ER:<Per-Target-Spec>), and over Host Adapter Prob-
              ing (NoProbe, NoProbeISA, NoSortPCI).

       EATA/DMA configuration
              The default list of i/o ports to be probed can be changed by


       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/driv-

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

       NCR53C8xx configuration


              where  S  is  a  comma-separated  string of items keyword:value.
              Recognized keywords are: mpar (master_parity),  spar  (scsi_par-
              ity),  disc  (disconnection),  specf  (special_features),  ultra
              (ultra_scsi), fsn (force_sync_nego), tags  (default_tags),  sync
              (default_sync),    verb    (verbose),   debug   (debug),   burst
              (burst_max).  For the  function  of  the  assigned  values,  see

       NCR53c406a configuration


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

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


              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  /usr/src/linux/driv-

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

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

              Also  note  that 'hd=' can be used to refer to the next unspeci-
              fied drive in the (a, ..., h) sequence.  For the following  dis-
              cussions,  the  'hd=' option will be cited for brevity.  See the
              file  Documentation/ide.txt  (or  drivers/block/README.ide   for
              older kernels) in the kernel source for more details.

       The 'hd=cyls,heads,sects[,wpcom[,irq]]' options
              These  options  are used to specify the physical geometry of the
              disk.  Only the first three values  are  required.   The  cylin-
              der/head/sectors  values will be those used by fdisk.  The write
              precompensation value is ignored for IDE disks.  The  IRQ  value
              specified  will be the IRQ used for the interface that the drive
              resides on, and is not really a drive-specific parameter.

       The 'hd=serialize' option
              The dual IDE interface CMD-640 chip is broken as  designed  such
              that when drives on the secondary interface are used at the same
              time as drives on the primary interface, it  will  corrupt  your
              data.  Using this option tells the driver to make sure that both
              interfaces are never used at the same time.

       The 'hd=dtc2278' option
              This option tells the driver  that  you  have  a  DTC-2278D  IDE
              interface.   The driver then tries to do DTC-specific operations
              to enable the second interface and  to  enable  faster  transfer

       The 'hd=noprobe' option
              Do not probe for this drive.  For example,

              hdb=noprobe hdb=1166,7,17

              would disable the probe, but still specify the drive geometry so
              that it would be registered as a valid block device,  and  hence

       The 'hd=nowerr' option
              Some  drives  apparently have the WRERR_STAT bit stuck on perma-
              nently.  This enables a work-around for these broken devices.

       The 'hd=cdrom' option
              This tells the IDE driver that there is an ATAPI compatible  CD-
              ROM  attached in place of a normal IDE hard disk.  In most cases
              the CD-ROM is identified automatically, but  if  it  isn't  then
              this may help.

       Standard ST-506 Disk Driver Options ('hd=')
              The  standard  disk driver can accept geometry arguments for the
              disks similar to the IDE driver.   Note  however  that  it  only
              expects  three  values (C/H/S); any more or any less and it will
              silently ignore you.  Also, it only accepts 'hd='  as  an  argu-
              ment,  that is, 'hda=' and so on are not valid here.  The format
              is as follows:


              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 syn-
              tax is as follows:


              Specifying an IRQ value of zero tells the driver  that  hardware
              interrupts  aren't  supported  (as  on some PAS cards).  If your
              card supports interrupts, you should use them as it cuts down on
              the CPU usage of the driver.

              The  is_pas_card should be entered as 'PAS' if using a Pro Audio
              Spectrum card, and otherwise it should not be specified at all.

       The CDU-535 Sony Interface
              The syntax for this CD-ROM interface is:


              A zero can be used for the I/O base as a  'placeholder'  if  one
              wishes to specify an IRQ value.

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


       The ISP16 CD-ROM Interface


              (three  integers  and  a  string).   If  the  type  is  given as
              'noisp16', the interface will not be configured.   Other  recog-
              nized types are: 'Sanyo", 'Sony', 'Panasonic' and 'Mitsumi'.

       The Mitsumi Standard Interface
              The syntax for this CD-ROM interface is:


              The  wait_value  is used as an internal timeout value for people
              who are having problems with their drive, and may or may not  be
              implemented  depending  on  a compile-time #define.  The Mitsumi
              FX400 is an IDE/ATAPI CD-ROM player and does  not  use  the  mcd

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


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


       The Phillips CM206 Interface
              The syntax for this type of card is:


              The driver assumes numbers between 3 and 11 are IRQ values,  and
              numbers  between 0x300 and 0x370 are I/O ports, so you can spec-
              ify one, or  both  numbers,  in  any  order.   It  also  accepts
              'cm206=auto' to enable autoprobing.

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


       The SoundBlaster Pro Interface
              The syntax for this type of card is:


              where  type  is  one  of the following (case sensitive) strings:
              'SoundBlaster', 'LaserMate', or 'SPEA'.  The I/O base is that of
              the  CD-ROM  interface, and not that of the sound portion of the

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


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

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


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

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

   The Floppy Disk Driver
       There are many floppy driver options, and they are all listed in  Docu-
       mentation/floppy.txt  (or drivers/block/README.fd for older kernels) in
       the kernel source.  This information is taken directly from that file.

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

              Sets the bit mask of allowed drives to all drives.  Use this  if
              you have more than two drives connected to a floppy controller.

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

              Tells the floppy driver that you have a well behaved floppy con-
              troller.  This allows more efficient and smoother operation, but
              may  fail  on  certain  controllers.   This may speed up certain

              Tells the floppy driver that your floppy  controller  should  be
              used with caution.

              Tells  the  floppy  driver  that you have only floppy controller

       floppy=two_fdc or floppy=address,two_fdc
              Tells the floppy driver that you have  two  floppy  controllers.
              The  second  floppy  controller is assumed to be at address.  If
              address is not given, 0x370 is assumed.

              Tells the floppy driver that you have a Thinkpad.  Thinkpads use
              an inverted convention for the disk change line.

              Tells the floppy driver that you don't have a Thinkpad.

              Sets  the  cmos type of drive to type.  Additionally, this drive
              is allowed in the bit mask.  This is useful  if  you  have  more
              than  two floppy drives (only two can be described in the physi-
              cal cmos), or if your BIOS uses non-standard CMOS  types.   Set-
              ting  the CMOS to 0 for the first two drives (default) makes the
              floppy driver read the physical cmos for those drives.

              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  /usr/src/linux/Documenta-

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


              The  parameters  maybe  given  as  integers,  or as strings.  If
              strings are used, then iobase and membase  should  be  given  in
              hexadecimal.   The integer arguments (fewer may be given) are in
              order:  status  (Enable(1)  or  Disable(0)  this   card),   type
              (PC/Xi(0),  PC/Xe(1),  PC/Xeve(2), PC/Xem(3)), altpin (Enable(1)
              or Disable(0) alternate pin arrangement),  numports  (number  of
              ports  on  this card), iobase (I/O Port where card is configured
              (in HEX)), membase (base of memory window (in HEX)).  Thus,  the
              following two boot prompt arguments are equivalent:


              More  details can be found in /usr/src/linux/Documentation/digi-

       The Baycom Serial/Parallel Radio Modem


              There are precisely 3 parameters; for several cards,  give  sev-
              eral  'baycom='  commands.  The modem parameter is a string that
              can take one of the values ser12, ser12*, par96,  par96*.   Here
              the  *  denotes that software DCD is to be used, and ser12/par96
              chooses between the supported modem types.   For  more  details,
              see   the  file  Documentation/networking/baycom.txt  (or  driv-
              ers/net/README.baycom for older kernels) in the kernel source.

       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-thresh-
              old, and the second the  y-threshold.   These  values  must  lie
              between 1 and 20 (inclusive); the default is 2.

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

       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 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux                             2007-12-16                      BOOTPARAM(7)