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BOOTPARAM(7)               Linux Programmer's Manual              BOOTPARAM(7)

       bootparam - Introduction to boot time parameters of the Linux kernel

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       'ro' and 'rw'
              The  'ro'  option tells the kernel to mount the root file system as 'read-only' so that file system con-
              sistency 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  mem-
              ory  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='

                   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

              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/ker-

              (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 acti-
              vation 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.   Mes-
              sages  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 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.

   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/Documenta-

       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 /usr/src/linux/Documentation/initrd.txt.

              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 informa-
       tion  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 '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

              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  upset-
              ting 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 source.

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

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


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

              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 set-
              ting, 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  per-
              mit 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 pro-
              ceed.  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 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 /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 Documentation/scsi/g_NCR5380.txt
              (or drivers/scsi/README.g_NCR5380 for older kernels) in the kernel source.

       NCR53C8xx configuration


              where  S is a comma-separated string of items keyword:value.  Recognized keywords are: mpar (master_par-
              ity), 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

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

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

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

       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 inter-
              face are used at the same time as drives on the primary interface, it will  corrupt  your  data.   Using
              this option tells the driver to make sure that both interfaces are never used at the same time.

       The 'hd=dtc2278' option
              This  option tells the driver that you have a DTC-2278D IDE interface.  The driver then tries to do DTC-
              specific operations to enable the second interface and to enable faster transfer modes.

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

              hdb=noprobe hdb=1166,7,17

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

       The 'hd=nowerr' option
              Some  drives  apparently  have  the WRERR_STAT bit stuck on permanently.  This enables a work-around for
              these broken devices.

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

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


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

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


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

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


       Syquest's EZ* removable disks


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

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


              For a ThinkPad-720, add the option


       IBM Microchannel SCSI Subsystem configuration


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

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


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

       Parallel port CD-ROM drives


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

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


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

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

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


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

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


       The ISP16 CD-ROM Interface


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

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


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

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

   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  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  auto-

              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 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 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 use-
              ful 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 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 inter-
              rupts only affect performance, and can safely be ignored.)

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


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

              T - device type: 1=FM, 2=SB, 3=PAS, 4=GUS, 5=MPU401, 6=SB16, 7=SB16-MPU401

              aaa - I/O address in hex.

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

              d - DMA channel.

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

   ISDN Drivers
       The ICN ISDN driver


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

       The PCBIT ISDN driver


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

       The Teles ISDN driver


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

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


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

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


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


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

       The Baycom Serial/Parallel Radio Modem


              There are precisely 3 parameters; for several cards, give several 'baycom=' commands.  The modem parame-
              ter  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 ker-
              nels) in the kernel source.

       Soundcard radio modem driver


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

   The Line Printer Driver
       'lp='  Syntax:


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

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

       WDT500/501 driver


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

              And precisely the same is true for the msmouse driver.

       ATARI mouse setup


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

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

       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  informa-
       tion is /usr/src/linux/Documentation/kernel-parameters.txt.

       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at

Linux                             2007-12-16                      BOOTPARAM(7)