Provided by: manpages_3.54-1ubuntu1_all bug


       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 arguments) separated by
       spaces.  Most of the boot arguments take have the form:


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

              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
              reverting  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 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  designed  only  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 argument 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 filesystem or hardware) must be loaded before the main disk can be accessed.

       In  Linux  1.3.48,  ramdisk  handling  was  changed  drastically.  Earlier, the memory was
       allocated statically, and there was a 'ramdisk=N' parameter to tell its size.  (This could
       also  be  set  in  the kernel image at compile time.)  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/blockdev/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

              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, 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  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 Linux 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
              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 busmastering 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 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  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 parameters, see the kernel
              source file drivers/scsi/BusLogic.c.  The text below is  a  very  much  abbreviated

              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 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  Documentation/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_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    the   kernel   source   file

       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 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 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 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 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
              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 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


       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 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 probe only 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  Linux  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 arguments to override the compiled in values.   This
       is  not  recommended, as it is rather complex.  It is described in the Linux kernel source
       file  Documentation/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, 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 argument 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 the kernel source file 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 the kernel source file 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 Linux 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


              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-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.


       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


       This page is part of release 3.54 of the Linux man-pages project.  A  description  of  the
       project,     and    information    about    reporting    bugs,    can    be    found    at