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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 details.

       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

       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 of:


       where 'name' is a unique keyword that is used to identify what  part  of  the  kernel  the
       associated  values  (if  any)  are  to  be given to.  Note the limit of 10 is real, as the
       present code only handles 10 comma separated parameters per keyword.   (However,  you  can
       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 argument.

       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 conventional.

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

       'ro' and 'rw'
              The  'ro'  option  tells the kernel to mount the root 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

                   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

       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


              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 source.

       Adaptec aha151x, aha152x, aic6260, aic6360, SB16-SCSI configuration
              The aha numbers refer to cards and the aic numbers refer to the actual SCSI chip on
              these type of cards, including the Soundblaster-16 SCSI.

              The probe code for these SCSI hosts looks for an installed BIOS,  and  if  none  is
              present,  the  probe will not find your card.  Then you will have to use a boot 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 5MB/s.

       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 source.

       NCR53C8xx configuration


              where S is a comma-separated string of items  keyword:value.   Recognized  keywords
              are:   mpar   (master_parity),  spar  (scsi_parity),  disc  (disconnection),  specf
              (special_features), ultra (ultra_scsi), fsn (force_sync_nego), tags (default_tags),
              sync  (default_sync),  verb  (verbose),  debug (debug), burst (burst_max).  For the
              function of the assigned values, see /usr/src/linux/drivers/scsi/ncr53c8xx.c.

       NCR53c406a configuration


              Specify irq = 0 for noninterrupt driven mode.  Set fastpio = 1 for fast pio mode, 0
              for slow mode.

       Pro Audio Spectrum configuration
              The   PAS16   uses  a  NC5380  SCSI  chip,  and  newer  models  support  jumperless
              configuration.  The boot 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/drivers/scsi/wd33c93.c.

   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 expected.

              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 modes.

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

              hdb=noprobe hdb=1166,7,17

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

       The 'hd=nowerr' option
              Some drives apparently have the WRERR_STAT bit stuck on permanently.  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
              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


       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 '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 driver.

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


       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 card.

   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 file.

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

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

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

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

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

              Tells the floppy driver that you have only floppy controller (default)

       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 ignored.)

   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, 7=SB16-MPU401

              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 identifier.

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


              More details can be found in /usr/src/linux/Documentation/riscom8.txt.

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


              The  parameters  maybe given as integers, or as strings.  If strings are used, then
              iobase and membase should be given in hexadecimal.  The  integer  arguments  (fewer
              may  be  given)  are  in  order:  status  (Enable(1) or Disable(0) this card), type
              (PC/Xi(0),  PC/Xe(1),  PC/Xeve(2),  PC/Xem(3)),  altpin  (Enable(1)  or  Disable(0)
              alternate  pin  arrangement),  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/digiboard.txt.

       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 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-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


       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