Man Linux: Main Page and Category List


       bootparam - Introduction to boot time parameters of the Linux kernel


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

       When  the  kernel  is booted directly by the BIOS (say from a floppy to
       which you copied a kernel using ’cp  zImage  /dev/fd0’),  you  have  no
       opportunity  to specify any parameters.  So, in order to take advantage
       of this possibility you have to use  software  that  is  able  to  pass
       parameters,  like  LILO  or loadlin.  For a few parameters one can also
       modify the kernel image itself, using rdev,  see  rdev(8)  for  further

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

       The  other  commonly  used  Linux  loader  is  ’LoadLin’ which is a DOS
       program that has the capability to launch a Linux kernel from  the  DOS
       prompt  (with boot-args) assuming that certain resources are available.
       This is good for people that want to launch Linux from DOS.

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

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


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

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

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

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

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

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

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

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

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

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

              This  argument tells the kernel what device is to be used as the
              root file system while booting.  The default of this setting  is
              determined at compile time, and usually is the value of the root
              device of the system that the kernel was built on.  To  override
              this  value,  and  select  the  second  floppy drive as the root
              device, one would use ’root=/dev/fd1’.   (The  root  device  can
              also be set using rdev(8).)

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

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

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

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

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

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

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


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

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

              For example, the boot line

              reserve=0x300,32  blah=0x300

              keeps all device drivers  except  the  driver  for  ’blah’  from
              probing 0x300-0x31f.

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

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

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

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

              By default the kernel will not reboot after a  panic,  but  this
              option  will  cause  a  kernel  reboot  after N seconds (if N is
              greater than zero).  This panic timeout can also be set by "echo
              N > /proc/sys/kernel/panic".

              (Only when CONFIG_BUGi386 is defined.)  Since 2.0.22 a reboot is
              by default a cold reboot.  One asks for  the  old  default  with
              ’reboot=warm’.   (A cold reboot may be required to reset certain
              hardware, but might destroy not  yet  written  data  in  a  disk
              cache.   A  warm  reboot may be faster.)  By default a reboot is
              hard, by asking the keyboard controller to pulse the reset  line
              low,  but  there  is at least one type of motherboard where that
              doesn’t  work.   The  option  ’reboot=bios’  will  instead  jump
              through the BIOS.

       ’nosmp’ and ’maxcpus=N’
              (Only  when  __SMP__  is  defined.)   A  command-line  option of
              ’nosmp’ or ’maxcpus=0’ will disable SMP activation entirely;  an
              option  ’maxcpus=N’  limits the maximum number of CPUs activated
              in SMP mode to N.

   Boot Arguments for Use by Kernel Developersdebug’
              Kernel messages are handed off to the kernel log daemon klogd so
              that they may be logged to disk.  Messages with a priority above
              console_loglevel are also printed on the  console.   (For  these
              levels,  see <linux/kernel.h>.)  By default this variable is set
              to log anything more important than debug messages.   This  boot
              argument  will  cause  the  kernel to also print the messages of
              DEBUG priority.  The console loglevel can also  be  set  at  run
              time via an option to klogd.  See klogd(8).

              It  is  possible  to  enable a kernel profiling function, if one
              wishes to find out where the kernel is spending its CPU  cycles.
              Profiling  is  enabled  by  setting the variable prof_shift to a
              nonzero value.  This is done either by specifying CONFIG_PROFILE
              at  compile  time,  or by giving the ’profile=’ option.  Now the
              value  that  prof_shift  gets  will  be  N,   when   given,   or
              CONFIG_PROFILE_SHIFT,  when  that  is  given, or 2, the default.
              The  significance  of  this  variable  is  that  it  gives   the
              granularity of the profiling: each clock tick, if the system was
              executing kernel code, a counter is incremented:

              profile[address >> prof_shift]++;

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

              Set   the   eight   parameters    max_page_age,    page_advance,
              page_decline,        page_initial_age,        age_cluster_fract,
              age_cluster_min, pageout_weight, bufferout_weight  that  control
              the kernel swap algorithm.  For kernel tuners only.

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

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

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

       There are four parameters, two boolean and two integral.

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

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

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

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

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

              For   a   detailed   description  of  the  initrd  feature,  see

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

   Boot Arguments for SCSI Devices
       General notation for this section:

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

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

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

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

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

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

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

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


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


              Full details can be found in the file  Documentation/scsi/st.txt
              (or  drivers/scsi/  for  older  kernels)  in the kernel

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

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


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

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


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

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


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

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

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

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


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

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



       BusLogic SCSI Hosts configuration (BusLogic=)


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

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

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

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


       Future Domain TMC-16x0 configuration


       Great Valley Products (GVP) SCSI controller configuration


       Future Domain TMC-8xx, TMC-950 configuration


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

       IN2000 configuration


              where S is a comma-separated string  of  items  keyword[:value].
              Recognized  keywords  (possibly  with  value)  are: ioport:addr,
              noreset, nosync:x,  period:ns,  disconnect:x,  debug:x,  proc:x.
              For     the     function     of     these     parameters,    see

       NCR5380 and NCR53C400 configuration
              The boot arg is of the form




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

       NCR53C8xx configuration


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

       NCR53c406a configuration


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

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


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

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


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

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


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

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


       WD7000 configuration


       Commodore Amiga A2091/590 SCSI controller configuration


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

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

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

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

              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 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.

              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

              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

              Some   drives  apparently  have  the  WRERR_STAT  bit  stuck  on
              permanently.   This  enables  a  work-around  for  these  broken

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

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


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

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


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

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


       Syquests EZ* removable disks


   IBM MCA Bus Devices
       See also /usr/src/linux/Documentation/mca.txt.

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


              For a ThinkPad-720, add the option


       IBM Microchannel SCSI Subsystem configuration


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

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


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

       Parallel port CD-ROM drives


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

       The CDU-31A and CDU-33A Sony Interface
              This CD-ROM interface is found on some of the Pro Audio Spectrum
              sound cards, and  other  Sony  supplied  interface  cards.   The
              syntax is as follows:


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

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

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


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

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


       The ISP16 CD-ROM Interface


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

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


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

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


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


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


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

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


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


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

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


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

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


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

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

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

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

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

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

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

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

              Tells the floppy driver that you  have  only  floppy  controller

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

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

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

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

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

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

   The Sound Driver
       The sound driver can also accept boot args to override the compiled  in
       values.   This  is  not  recommended,  as  it is rather complex.  It is
       described in the kernel source file  Documentation/sound/oss/README.OSS
       (drivers/sound/Readme.linux  in  older  kernel versions).  It accepts a
       boot arg of the form:


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

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

              aaa - I/O address in hex.

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

              d - DMA channel.

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

   ISDN Drivers
       The ICN ISDN driver


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

       The PCBIT ISDN driver


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

       The Teles ISDN driver


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

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


              More        details        can        be        found         in

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


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


              More        details        can        be        found         in

       The Baycom Serial/Parallel Radio Modem


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

       Soundcard radio modem driver


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

   The Line Printer Driverlp=’  Syntax:


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

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

       WDT500/501 driver


   Mouse Driversbmouse=irq’
              The  busmouse  driver only accepts one parameter, that being the
              hardware IRQ value to be used.

              And precisely the same is true for the msmouse driver.

       ATARI mouse setup


              If only one argument is given, it is used for  both  x-threshold
              and  y-threshold.   Otherwise,  the  first  argument  is  the x-
              threshold, and the second the y-threshold.   These  values  must
              lie between 1 and 20 (inclusive); the default is 2.

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


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

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


       This  page  is  part of release 3.24 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at