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       bootparam - Introduction to boot time parameters of the Linux kernel


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

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

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


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


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

       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

       (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 also be set using rdev(8).)

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

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

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

       The ‘ro’ option tells the  kernel  to  mount  the  root  filesystem  as
       ‘readonly’  so that filesystem consistency check programs (fsck) can do
       their work on a quiescent file system. No processes can write to  files
       on  the  filesystem  in  question until it is ‘remounted’ as read/write
       capable, e.g., 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.

       The  choice  between  read-only  and  read/write  can also be set using

       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

       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
       cacheing 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.’’

       By default the kernel will not reboot after a panic,  but  this  option
       will  cause  a  kernel  reboot  after N seconds (if N > 0).  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.

       (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.


       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

       It is possible to enable a kernel profiling function, if one wishes  to
       find  out  where  the  kernel is spending its CPU cycles.  Profiling is
       enabled by setting the variable prof_shift to a non-zero value. This is
       done  either by specifying CONFIG_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.


       (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, or by use of rdev(8).)  These days ram disks  use  the
       buffer  cache,  and  grow dynamically.  For a lot of information (e.g.,
       how to use rdev(8) in conjunction with  the  new  ramdisk  setup),  see

       There are four parameters, two boolean and two integral.

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

       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=Nor (obsolete)ramdisk=N’
       Set  the maximal size of the ramdisk(s) to N kB. The default is 4096 (4

       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 filesystem is moved over to  /initrd;
       finally  the  usual  boot  sequence  (e.g. invocation of /sbin/init) is

       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.)


       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
       behaviour as a boot argument.

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

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

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

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


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


       Full  details  can  be  found in the file that is in the scsi
       directory of the kernel source tree.

   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 non-zero
       value is used. An example usage is as follows:


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

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


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

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

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

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


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

   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 /usr/src/linux/drivers/scsi/in2000.c.

   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

   NCR53C8xx configuration

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

   NCR53c406a configuration

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

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


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

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


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

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


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

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


   WD7000 configuration

   Commodore Amiga A2091/590 SCSI controller configuration

       where S is a comma-separated string of options. Recognized options  are
       nosync:bitmask,  nodma:x,  period:ns,  disconnect:x,  debug:x, clock:x,
       next. For details, see /usr/src/linux/drivers/scsi/wd33c93.c.


   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  README.ide   in
       linux/drivers/block 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 modes.

       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.

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

       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, i.e. ‘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 recognised, 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


       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


       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.  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

   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.


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


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


       There  are  many  floppy  driver  options,  and  they are all listed in
       README.fd in linux/drivers/block. This information  is  taken  directly
       from that file.

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

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

       Sets the bitmask 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

       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 bitmask. 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 non-standard 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 behaviour)

   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 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 Readme.Linux file, in linux/drivers/sound. 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.


   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.


   The RISCom/8 Multiport Serial Driver (riscom8=)


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

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


       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

   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.




       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



       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.


       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


       Linus Torvalds (and many others)


       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.