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



NAME
       bootparam - introduction to boot time parameters of the Linux kernel

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

       When the kernel is booted directly by the BIOS (say from a floppy to which  you  copied  a
       kernel  using  'cp  zImage  /dev/fd0'), you have no opportunity to specify any parameters.
       So, in order to take advantage of this possibility you have to use a boot loader  that  is
       able to pass parameters, such as GRUB.


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

           name[=value_1][,value_2]...[,value_10]

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

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

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

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

       Any  remaining arguments that were not picked up by the kernel and were not interpreted as
       environment variables are then passed onto process one, which is usually the init(1)  pro‐
       gram.   The  most  common argument that is passed to the init process is the word 'single'
       which instructs it to boot the computer in single user mode, and not launch all the  usual
       daemons.  Check the manual page for the version of init(1) installed on your system to see
       what arguments it accepts.

   General non-device-specific boot arguments
       'init=...'
              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.

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

       'nfsroot=...'
              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.

       'no387'
              (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 calcula‐
              tions.  Using the 'no387' boot argument causes Linux to ignore the maths  coproces‐
              sor  even  if you have one.  Of course you must then have your kernel compiled with
              math emulation support!

       'no-hlt'
              (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.

       'root=...'
              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 usu‐
              ally is the value of the root device of the system that the kernel  was  built  on.
              To  override this value, and select the second floppy drive as the root device, one
              would use 'root=/dev/fd1'.

              The root device can be specified symbolically or numerically.  A symbolic  specifi‐
              cation 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 par‐
              allel 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 flop‐
              pies).  Recent kernels allow many other types, mostly for CD-ROMs: nfs,  ram,  scd,
              mcd,  cdu535, aztcd, cm206cd, gscd, sbpcd, sonycd, bpcd.  (The type nfs specifies a
              net boot; ram refers to a ram disk.)

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

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

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

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

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

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

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


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

                  resume=/dev/hda2

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

                  reserve=iobase,extent[,iobase,extent]...

              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.

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

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

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

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

       'panic=N'
              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

       'reboot=[warm|cold][,[bios|hard]]'
              (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 num‐
              ber of CPUs activated in SMP mode to N.

   Boot arguments for use by kernel developers
       'debug'
              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  vari‐
              able 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).

       'profile=N'
              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 CON‐
              FIG_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.

       'swap=N1,N2,N3,N4,N5,N6,N7,N8'
              Set  the  eight  parameters  max_page_age,  page_advance,  page_decline,  page_ini‐
              tial_age, age_cluster_fract, age_cluster_min, pageout_weight, bufferout_weight that
              control the kernel swap algorithm.  For kernel tuners only.

       'buff=N1,N2,N3,N4,N5,N6'
              Set the six parameters max_buff_age, buff_advance, buff_decline,  buff_initial_age,
              bufferout_weight,  buffermem_grace  that  control  kernel buffer memory management.
              For kernel tuners only.

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

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

       There are four parameters, two boolean and two integral.

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

       'prompt_ramdisk=N'
              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).

       'ramdisk_start=N'
              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.

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

              For  a detailed description of the initrd feature, see the kernel source file Docu‐
              mentation/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 hexadec‐
       imal notation, and usually lie in the range from 0x200 to 0x3ff.

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

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

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

       'max_scsi_luns=...'
              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:

                  st=buf_size[,write_threshold[,max_bufs]]

              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:

                  st=32,30,2

              Full  details  can  be  found  in  the  file  Documentation/scsi/st.txt  (or  driv‐
              ers/scsi/README.st for older kernels) in the Linux kernel source.

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

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

                  aha152x=iobase[,irq[,scsi-id[,reconnect[,parity]]]]

              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  exam‐
              ple usage is as follows:

                  aha152x=0x340,11,7,1

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

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

                  aha1542=iobase[,buson,busoff[,dmaspeed]]

              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 domi‐
              nates 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  han‐
              dling it.  Experiment with caution if using values over 5MB/s.

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

                  aic7xxx=extended,no_reset

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

       AdvanSys SCSI Hosts configuration ('advansys=')
              The  AdvanSys driver can accept up to four I/O addresses that will be probed for an
              AdvanSys SCSI card.  Note that these values (if used) do not  effect  EISA  or  PCI
              probing  in  any  way.  They are used only for probing ISA and VLB cards.  In addi‐
              tion, if the driver has been compiled with debugging enabled, the level  of  debug‐
              ging  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.

       AM53C974
              Syntax:

                  AM53C974=host-scsi-id,target-scsi-id,max-rate,max-offset

       BusLogic SCSI Hosts configuration ('BusLogic=')

              Syntax:
                  BusLogic=N1,N2,N3,N4,N5,S1,S2,...

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

                  eata=iobase,iobase,....

       Future Domain TMC-16x0 configuration
              Syntax:

                  fdomain=iobase,irq[,adapter_id]

       Great Valley Products (GVP) SCSI controller configuration
              Syntax:

                  gvp11=dma_transfer_bitmask

       Future Domain TMC-8xx, TMC-950 configuration
              Syntax:

                  tmc8xx=mem_base,irq

              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
              Syntax:

                  in2000=S

              where S is a comma-separated string of items keyword[:value].  Recognized  keywords
              (possibly with value) are: ioport:addr, noreset, nosync:x, period:ns, disconnect:x,
              debug:x, proc:x.  For the function of these parameters, see the kernel source  file
              drivers/scsi/in2000.c.

       NCR5380 and NCR53C400 configuration
              The boot argument is of the form

                  ncr5380=iobase,irq,dma

              or

                  ncr53c400=iobase,irq

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

       NCR53C8xx configuration
              Syntax:

                  ncr53c8xx=S

              where S is a comma-separated string of items  keyword:value.   Recognized  keywords
              are:  mpar  (master_parity),  spar (scsi_parity), disc (disconnection), specf (spe‐
              cial_features), ultra (ultra_scsi),  fsn  (force_sync_nego),  tags  (default_tags),
              sync  (default_sync),  verb  (verbose),  debug (debug), burst (burst_max).  For the
              function  of  the   assigned   values,   see   the   kernel   source   file   driv‐
              ers/scsi/ncr53c8xx.c.

       NCR53c406a configuration
              Syntax:

                  ncr53c406a=iobase[,irq[,fastpio]]

              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  configura‐
              tion.  The boot argument is of the form:

                  pas16=iobase,irq

              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 argu‐
              ment of the form:

                  st0x=mem_base,irq

              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:

                  t128=mem_base,irq

              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

                  eata=iobase,iobase,....

       WD7000 configuration
              Syntax:

                  wd7000=irq,dma,iobase

       Commodore Amiga A2091/590 SCSI controller configuration
              Syntax:

                  wd33c93=S

              where S is a comma-separated string of options.  Recognized options are nosync:bit‐
              mask,  nodma:x,  period:ns, disconnect:x, debug:x, clock:x, next.  For details, see
              the kernel source file drivers/scsi/wd33c93.c.

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

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

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

       The 'hd=cyls,heads,sects[,wpcom[,irq]]' options
              These  options  are  used  to  specify the physical geometry of the disk.  Only the
              first three values are required.  The cylinder/head/sectors values  will  be  those
              used  by fdisk.  The write precompensation value is ignored for IDE disks.  The IRQ
              value specified will be the IRQ used for the interface that the drive  resides  on,
              and is not really a drive-specific parameter.

       The 'hd=serialize' option
              The  dual IDE interface CMD-640 chip is broken as designed such that when drives on
              the secondary interface are used at the same time as drives on the  primary  inter‐
              face,  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 automati‐
              cally, but if it isn't then this may help.

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

                  hd=cyls,heads,sects

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

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

                  xd=type,irq,iobase,dma_chan

              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:

                  xd=2,5,0x320,3

       Syquest's EZ* removable disks
              Syntax:

                  ez=iobase[,irq[,rep[,nybble]]]

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

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

                  ed=cyls,heads,sectors.

              For a ThinkPad-720, add the option

                  tp720=1.

       IBM Microchannel SCSI Subsystem configuration
              Syntax:

                  ibmmcascsi=N

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

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

                  aztcd=iobase[,magic_number]

              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
              Syntax:

                  pcd.driveN=prt,pro,uni,mod,slv,dly
                  pcd.nice=nice

              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 auto‐
              matically), '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:

                  cdu31a=iobase,[irq[,is_pas_card]]

              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:

                  sonycd535=iobase[,irq]

              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:

                  gscd=iobase

       The ISP16 CD-ROM Interface
              Syntax:

                  isp16=[iobase[,irq[,dma[,type]]]]

              (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:

                  mcd=iobase,[irq[,wait_value]]

              The wait_value is used as an internal timeout value for people who are having prob‐
              lems 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.  Syn‐
              tax:

                  mcdx=iobase[,irq]

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

                  optcd=iobase

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

                  cm206=[iobase][,irq]

              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:

                  sjcd=iobase[,irq[,dma_channel]]

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

                  sbpcd=iobase,type

              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:

           ether=irq,iobase[,param_1[,...param_8]],name

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

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

           ether=0,0,eth1

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

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

   The floppy disk driver
       There are many floppy driver options, and they are all listed in  Documentation/floppy.txt
       (or  drivers/block/README.fd for older kernels) in the Linux kernel source.  This informa‐
       tion is taken directly from that file.

       floppy=mask,allowed_drive_mask
              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 hard‐
              ware (ASUS PCI motherboards) mess up the keyboard when  accessing  units  2  or  3.
              This option is somewhat obsoleted by the cmos option.

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

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

       floppy=daring
              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.

       floppy=0,daring
              Tells the floppy driver that your floppy controller should be used with caution.

       floppy=one_fdc
              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.

       floppy=thinkpad
              Tells  the  floppy driver that you have a Thinkpad.  Thinkpads use an inverted con‐
              vention for the disk change line.

       floppy=0,thinkpad
              Tells the floppy driver that you don't have a Thinkpad.

       floppy=drive,type,cmos
              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.  Set‐
              ting  the CMOS to 0 for the first two drives (default) makes the floppy driver read
              the physical cmos for those drives.

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

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

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

           sound=device1[,device2[,device3...[,device10]]]

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

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

              aaa - I/O address in hex.

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

              d - DMA channel.

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

   ISDN drivers
       The ICN ISDN driver
              Syntax:

                  icn=iobase,membase,icn_id1,icn_id2

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

       The PCBIT ISDN driver
              Syntax:

                  pcbit=membase1,irq1[,membase2,irq2]

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

       The Teles ISDN driver
              Syntax:

                  teles=iobase,irq,membase,protocol,teles_id

              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=')
              Syntax:

                  riscom=iobase1[,iobase2[,iobase3[,iobase4]]]

              More details can be found in the kernel source file Documentation/riscom8.txt.

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

                  digi=status,type,altpin,numports,iobase,membase

              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) alter‐
              nate 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:

                  digi=E,PC/Xi,D,16,200,D0000
                  digi=1,0,0,16,0x200,851968

              More details can be found in the kernel source file Documentation/digiboard.txt.

       The Baycom Serial/Parallel Radio Modem
              Syntax:

                  baycom=iobase,irq,modem

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

       Soundcard radio modem driver
              Syntax:

                  soundmodem=iobase,irq,dma[,dma2[,serio[,pario]]],0,mode

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

   The line printer driver
       'lp='
              Syntax:

                  lp=0
                  lp=auto
                  lp=reset
                  lp=port[,port...]

              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
              Syntax:

                  wdt=io,irq

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

       'msmouse=irq'
              And precisely the same is true for the msmouse driver.

       ATARI mouse setup
              Syntax:

                  atamouse=threshold[,y-threshold]

              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
       'no-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.

SEE ALSO
       klogd(8), mount(8)

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

COLOPHON
       This  page  is  part of release 3.74 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2014-06-13                               BOOTPARAM(7)


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