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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 a boot loader that is able to  pass
       parameters, such as GRUB.

   The argument list
       The  kernel  command  line is parsed into a list of strings (boot argu-
       ments) separated by spaces.  Most of the boot arguments take  have  the


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

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

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

       Anything of the form 'foo=bar' that is not accepted as a setup function
       as described above is then interpreted as an environment variable to be
       set.  A (useless?) example would be to use 'TERM=vt100' as a boot 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(1) program.  The most common argument
       that is passed to the init process is the word 'single' which instructs
       it  to  boot  the  computer in single user mode, and not launch all the
       usual daemons.  Check the  manual  page  for  the  version  of  init(1)
       installed on your system to see what arguments it accepts.

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

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

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

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

              (Only  when  CONFIG_BUGi386  is  defined.)   Some  of  the early
              i486DX-100 chips have a problem with the 'hlt'  instruction,  in
              that  they  can't  reliably  return to operating mode after this
              instruction is used.  Using the 'no-hlt' instruction tells Linux
              to  just  run an infinite loop when there is nothing else to do,
              and to not halt the CPU.  This allows people with  these  broken
              chips to use Linux.

              This  argument tells the kernel what device is to be used as the
              root filesystem while booting.  The default of this  setting  is
              determined at compile time, and usually is the value of the root
              device of the system that the kernel was built on.  To  override
              this  value,  and  select  the  second  floppy drive as the root
              device, one would use 'root=/dev/fd1'.

              The root device can be specified symbolically or numerically.  A
              symbolic  specification  has the form /dev/XXYN, where XX 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 filesystem.  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.   (For  example, /dev/sda3 is major 8, minor 3, so you
              could use 'root=0x803' as an alternative.)

              This parameter sets the  delay  (in  seconds)  to  pause  before
              attempting to mount the root filesystem.

              This  parameter  sets  the  mount  option  string  for  the root
              filesystem (see also fstab(5)).

              The 'rootfstype' option tells  the  kernel  to  mount  the  root
              filesystem  as  if  it where of the type specified.  This can be
              useful (for example) to mount an ext3  filesystem  as  ext2  and
              then  remove the journal in the root filesystem, in fact revert-
              ing its format from ext3 to ext2 without the need  to  boot  the
              box from alternate media.

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

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

              This  tells  the kernel the location of the suspend-to-disk data
              that you want the machine  to  resume  from  after  hibernation.
              Usually, it is the same as your swap partition or file. Example:


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


              In some machines it may be necessary to prevent  device  drivers
              from  checking  for devices (auto-probing) in a specific region.
              This may be because of hardware that reacts badly to  the  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  designed  only 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 argument to  tell  Linux
              how  much memory you have.  The value is in decimal or hexadeci-
              mal (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:  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_PRO-
              FILE_SHIFT, when that is given, or 2, the default.  The signifi-
              cance 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 filesystem or hardware) must be  loaded  before  the  main
       disk can be accessed.

       In  Linux  1.3.48,  ramdisk handling was changed drastically.  Earlier,
       the memory was allocated statically, and there was a 'ramdisk=N' param-
       eter  to tell its size.  (This could also be set in the kernel image at
       compile time.)  These days ram disks use the  buffer  cache,  and  grow
       dynamically.   For  a  lot  of  information in conjunction with the new
       ramdisk  setup,  see  the  kernel  source   file   Documentation/block-
       dev/ramdisk.txt (Documentation/ramdisk.txt in older kernels).

       There are four parameters, two boolean and two integral.

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

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

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

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

              (Only  if  the  kernel  was compiled with CONFIG_BLK_DEV_RAM and
              CONFIG_BLK_DEV_INITRD.)  These days it is  possible  to  compile
              the  kernel  to  use  initrd.  When this feature is enabled, the
              boot process will load the kernel and an initial  ramdisk;  then
              the  kernel  converts  initrd  into a "normal" ramdisk, which is
              mounted read-write as root device; then  /linuxrc  is  executed;
              afterward  the "real" root filesystem is mounted, and the initrd
              filesystem is moved over to  /initrd;  finally  the  usual  boot
              sequence (e.g., invocation of /sbin/init) is performed.

              For a detailed description of the initrd feature, see the kernel
              source file Documentation/initrd.txt.

              The 'noinitrd' option tells the kernel that although it was 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, and
       so on.

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

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

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

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

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

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


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


              Full details can be found in the file  Documentation/scsi/st.txt
              (or  drivers/scsi/ for older kernels) in the Linux ker-
              nel 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 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 argument of the form:


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

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


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

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


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

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

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

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


              The extended value, if nonzero, indicates that extended transla-
              tion 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 val-
              ues (if used) do not effect EISA or  PCI  probing  in  any  way.
              They  are used only for probing ISA and VLB cards.  In addition,
              if the driver has been  compiled  with  debugging  enabled,  the
              level  of  debugging  output  can be set by adding an 0xdeb[0-f]
              parameter.  The 0-f allows setting the level  of  the  debugging
              messages to any of 16 levels of verbosity.



       BusLogic SCSI Hosts configuration ('BusLogic=')


              For an extensive discussion of the BusLogic command line parame-
              ters, see the kernel source file  drivers/scsi/BusLogic.c.   The
              text below is a very much abbreviated extract.

              The  parameters  N1-N5  are integers.  The parameters S1,... are
              strings.  N1 is the I/O Address at which  the  Host  Adapter  is
              located.  N2 is the Tagged Queue Depth to use for Target Devices
              that support Tagged Queuing.  N3 is the Bus Settle Time in  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 the kernel source file

       NCR5380 and NCR53C400 configuration
              The boot argument is of the form




              If the card doesn't use interrupts, then an  IRQ  value  of  255
              (0xff)  will  disable  interrupts.  An IRQ value of 254 means to
              autoprobe.  More details can be found  in  the  file  Documenta-
              tion/scsi/g_NCR5380.txt  (or  drivers/scsi/README.g_NCR5380  for
              older kernels) in the Linux kernel source.

       NCR53C8xx configuration


              where S is a  comma-separated  string  of  items  keyword:value.
              Recognized  keywords  are: mpar (master_parity), spar (scsi_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 the
              kernel source file drivers/scsi/ncr53c8xx.c.

       NCR53c406a configuration


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

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


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

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


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

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


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

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


       WD7000 configuration


       Commodore Amiga A2091/590 SCSI controller configuration


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

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

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

              Also note that 'hd=' can be used to refer to the  next  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 Linux kernel source for more details.

       The 'hd=cyls,heads,sects[,wpcom[,irq]]' options
              These options are used to specify the physical geometry  of  the
              disk.   Only  the  first  three values are required.  The 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 expects
              only three values (C/H/S); any more or  any  less  and  it  will
              silently  ignore  you.   Also, it accepts only 'hd=' as an 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 argument of the form:


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

              The  xd_setup()  function  does  no  checking on the values, and
              assumes that you entered all four values.  Don't disappoint  it.
              Here  is  an example usage for a WD1002 controller with the BIOS
              disabled/removed, using the 'default' XT controller parameters:


       Syquest's EZ* removable disks


   IBM MCA bus devices
       See also the kernel source file Documentation/mca.txt.

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


              For a ThinkPad-720, add the option


       IBM Microchannel SCSI Subsystem configuration


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

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


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

       Parallel port CD-ROM drives


              where 'port' is the base address, 'pro' is the protocol  number,
              'uni'  is  the unit selector (for chained devices), 'mod' is the
              mode (or -1 to choose the best automatically), 'slv' is 1 if  it
              should be a slave, and 'dly' is a small integer for slowing down
              port accesses.  The 'nice' parameter controls the  driver's  use
              of idle CPU time, at the expense of some speed.

       The CDU-31A and CDU-33A Sony Interface
              This CD-ROM interface is found on some of the Pro Audio Spectrum
              sound cards, and other Sony supplied interface cards.  The  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 nonnumeric argument is taken as the name.  The param_n values
       (if applicable) usually have  different  meanings  for  each  different
       card/driver.   Typical  param_n  values are used to specify things like
       shared memory address, interface selection, DMA channel and the like.

       The most common use of this parameter is to force probing for a  second
       ethercard, as the default is to probe only for one.  This can be accom-
       plished 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 Linux kernel source.  This information is taken directly from  that

              Sets  the  bit mask of allowed drives to mask.  By default, only
              units 0 and 1 of each floppy controller are  allowed.   This  is
              done  because  certain  nonstandard  hardware  (ASUS PCI 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 nonstandard CMOS types.  Setting
              the CMOS to 0 for the  first  two  drives  (default)  makes  the
              floppy driver read the physical cmos for those drives.

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

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

   The sound driver
       The sound driver can also accept boot arguments to  override  the  com-
       piled in values.  This is not recommended, as it is rather complex.  It
       is   described   in   the   Linux   kernel   source   file   Documenta-
       tion/sound/oss/README.OSS  (drivers/sound/Readme.linux  in older kernel
       versions).  It accepts a boot argument of the form:


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

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

              aaa - I/O address in hex.

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

              d - DMA channel.

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

   ISDN drivers
       The ICN ISDN driver


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

       The PCBIT ISDN driver


              where membaseN is the shared memory base of the N'th  card,  and
              irqN  is the interrupt setting of the N'th card.  The default is
              IRQ 5 and membase 0xD0000.

       The Teles ISDN driver


              where iobase is the I/O port address of the card, membase is the
              shared  memory  base  address  of the card, irq is the interrupt
              channel the card uses, and teles_id is the unique  ASCII  string

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


              More  details  can be found in the kernel source file 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 the kernel source file Documenta-

       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  Linux  kernel

       Soundcard radio modem driver


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

   The line printer driver


              You can tell the printer driver what ports to use and what ports
              not  to  use.   The  latter comes in handy if you don't want the
              printer driver to claim all available parallel  ports,  so  that
              other drivers (e.g., PLIP, PPA) can use them instead.

              The format of the argument is multiple port names.  For example,
              lp=none,parport0 would use the first parallel port for lp1,  and
              disable  lp0.   To  disable the printer driver entirely, one can
              use lp=0.

       WDT500/501 driver


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

              And precisely the same is true for the msmouse driver.

       ATARI mouse setup


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

       klogd(8), mount(8)

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

       This  page  is  part of release 3.74 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at

Linux                             2014-06-13                      BOOTPARAM(7)

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