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 parame-
ters. So, in order to take advantage of this possibility
you have to use software that is able to pass parameters,
like LILO or loadlin. For a few parameters one can also
modify the kernel image itself, using rdev, see rdev(8)
for further details.
The LILO program (LInux LOader) written by Werner Almes-
berger is the most commonly used. It has the ability to
boot various kernels, and stores the configuration infor-
mation in a plain text file. (See lilo(8) and
lilo.conf(5).) LILO can boot DOS, OS/2 Linux, FreeBSD,
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 Compati-
ble' sound cards that require the DOS driver to twiddle a
few mystical registers to put the card into a SB compati-
ble 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
Most of the boot args take the form of:
name[=value_1][,value_2]...[,value_11]
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. Multiple boot args are just a space sepa-
rated list of the above format. Note the limit of 11 is
real, as the present code only handles 11 comma separated
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parameters per keyword. (However, you can re-use the same
keyword with up to an additional 11 parameters in unusu-
ally 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=', `ro', `rw', or `debug'. The
meaning of these special arguments is described further on
in the document.
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 funtion 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 ver-
sion of init installed on your system to see what argu-
ments it accepts.
GENERAL NON-DEVICE SPECIFIC BOOT ARGS
`no387'
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 per-
forming floating point calculations. Using the `no387'
boot arg causes Linux to ignore the maths coprocessor even
if you have one. Of course you must then have your kernel
compiled with math emulation support!
`no-hlt'
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
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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 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 numeri-
cally. A symbolic specification has the form /dev/XXYN,
where XX designates the device type (`hd' for ST-506 com-
patible hard disk, with Y in `a'-`h'; `sd' for SCSI com-
patible disk, with Y in `a'-`e'; `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 num-
ber, and N the number of the partition on this device
(absent in the case of floppies).
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
filesystem as `readonly' so that filesystem consistency
check programs (fsck) can do their work on a quiescent
file system. No processes can write to files on the
filesystem in question until it is `remounted' as
read/write capable, e.g., by `mount -w -n -o remount /'.
(See also mount(8).)
The `rw' option tells the kernel to mount the root
filesystem read/write. This is the default.
The choice between read-only and read/write can also be
set using rdev(8).
`debug'
Kernel messages are handed off to the kernel log daemon
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klogd so that they may be logged to disk. Messages with a
priority above console_loglevel are also printed on the
console. (For these levels, see <linux/kernel.h>.) By
default this variable is set to log anything more impor-
tant 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).
`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 spe-
cific 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.
`ramdisk=...'
This option is obsolete since Linux 1.3.48 or so. It
specifies the size in kB of the optional RAM disk device.
For example, if one wished to have a root filesystem on a
1.44MB floppy loaded into the RAM disk device, they would
use:
ramdisk=1440
This option is set at compile time (default: no RAM disk),
and can be modified using rdev(8).
`mem=...'
The BIOS call defined in the PC specification that returns
the amount of installed memory was only designed to be
able to report up to 64MB. Linux uses this BIOS call at
boot to determine how much memory is installed. If you
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have more than 64MB of RAM installed, you can use this
boot arg to tell Linux how much memory you have. The
value is in decimal or hexadecimal (prefix 0x), and the
suffixes `k' (times 1024) or `M' (times 1048576) can be
used. Here is a quote from Linus on usage of the `mem='
parameter.
``The kernel will accept any `mem=xx' parameter you give
it, and if it turns out that you lied to it, it will crash
horribly sooner or later. The parameter indicates the
highest addressable RAM address, so `mem=0x1000000' means
you have 16MB of memory, for example. For a 96MB machine
this would be `mem=0x6000000'.
NOTE NOTE NOTE: some machines might use the top of memory
for BIOS cacheing or whatever, so you might not actually
have up to the full 96MB addressable. The reverse is also
true: some chipsets will map the physical memory that is
covered by the BIOS area into the area just past the top
of memory, so the top-of-mem might actually be 96MB +
384kB for example. If you tell linux that it has more
memory than it actually does have, bad things will happen:
maybe not at once, but surely eventually.''
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 hexidecimal 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 speci-
fied 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 infor-
mation exchanges. Specifying a one indicates parity
checking is enabled, and a zero disables parity checking.
Again, not all adapters will support selection of parity
behaviour as a boot argument.
`max_scsi_luns=...'
A SCSI device can have a number of `sub-devices' contained
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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 com-
pile 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 README.st file that is in
the scsi directory of the kernel source tree.
Adaptec aha151x, aha152x, aic6260, aic6360, SB16-SCSI configu-
ration
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:
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.
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All the parameters are as described at the top of this
section, and the reconnect value will allow device discon-
nect/reconnect if a non-zero value is used. An example
usage is as follows:
aha152x=0x340,11,7,1
Note that the parameters must be specified in order, mean-
ing 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 ``fair-
ness'' that is used to share the bus with other devices.
The boot arg 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 microsec-
onds that the card dominates the ISA bus. The defaults are
11us on, and 4us off, so that other cards (such as an ISA
LANCE Ethernet card) have a chance to get access to the
ISA bus.
The dmaspeed value refers to the rate (in MB/s) at which
the DMA (Direct Memory Access) transfers proceed. The
default is 5MB/s. Newer revision cards allow you to
select this value as part of the soft-configuration, older
cards use jumpers. You can use values up to 10MB/s assum-
ing 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:
aic7xxx=extended,no_reset
The extended value, if non-zero, indicates that extended
translation for large disks is enabled. The no_reset
value, if non-zero, tells the driver not to reset the SCSI
bus when setting up the host adaptor at boot.
BusLogic SCSI Hosts configuration (`buslogic=')
At present, the buslogic driver accepts only one
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parameter, that being the I/O base. It expects that to be
one of the following valid values: 0x130, 0x134, 0x230,
0x234, 0x330, 0x334.
Future Domain TMC-8xx, TMC-950 configuration
If your card is not detected at boot time, you will then
have to use a boot arg of the form:
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.
Pro Audio Spectrum configuration
The PAS16 uses a NC5380 SCSI chip, and newer models sup-
port jumperless configuration. The boot arg 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 arg 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.
Cards that don't Accept Boot Args
At present, the following SCSI cards do not make use of
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any boot-time parameters. In some cases, you can hard-wire
values by directly editing the driver itself, if required.
Always IN2000, Adaptec aha1740, EATA-DMA, EATA-PIO, Future
Domain 16xx, NCR5380 (generic), NCR53c7xx to NCR53c8xx,
Qlogic, Ultrastor (incl. u?4f), Western Digital wd7000.
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 README.ide in linux/drivers/block
for more details.
The `hd=cyls,heads,sects[,wpcom[,irq]]' options
These options are used to specify the physical geometry of
the disk. Only the first three values are required. The
cylinder/head/sectors values will be those used by fdisk.
The write precompensation value is ignored for IDE disks.
The IRQ value specified will be the IRQ used for the
interface that the drive resides on, and is not really a
drive specific parameter.
The `hd=serialize' option
The dual IDE interface CMD-640 chip is broken as designed
such that when drives on the secondary interface are used
at the same time as drives on the primary interface, it
will corrupt your data. Using this option tells the driver
to make sure that both interfaces are never used at the
same time.
The `hd=dtc2278' option
This option tells the driver that you have a DTC-2278D IDE
interface. The driver then tries to do DTC specific oper-
ations to enable the second interface and to enable faster
transfer modes.
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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 geom-
etry so that it would be registered as a valid block
device, and hence useable.
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 compati-
ble CD-ROM attached in place of a normal IDE hard disk. In
most cases the CD-ROM is identified automatically, but if
it isn't then this may help.
Standard ST-506 Disk Driver Options (`hd=')
The standard disk driver can accept geometry arguments for
the disks similar to the IDE driver. Note however that it
only expects three values (C/H/S) -- any more or any less
and it will silently ignore you. Also, it only accepts
`hd=' as an argument, i.e. `hda=' and so on are not valid
here. The format is as follows:
hd=cyls,heads,sects
If there are two disks installed, the above is repeated
with the geometry parameters of the second disk.
XT Disk Driver Options (`xd=')
If you are unfortunate enough to be using one of these old
8 bit cards that move data at a whopping 125kB/s then here
is the scoop. If the card is not recognised, you will
have to use a boot arg of the form:
xd=type,irq,iobase,dma_chan
The type value specifies the particular manufacturer of
the card, and are as follows: 0=generic; 1=DTC;
2,3,4=Western Digital, 5,6,7=Seagate; 8=OMTI. The only
difference between multiple types from the same manufac-
turer is the BIOS string used for detection, which is not
used if the type is specified.
The xd_setup() function does no checking on the values,
and assumes that you entered all four values. Don't
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disappoint it. Here is an example usage for a WD1002 con-
troller with the BIOS disabled/removed, using the
`default' XT controller parameters:
xd=2,5,0x320,3
CD-ROMs (Non-SCSI/ATAPI/IDE)
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.
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 speci-
fied 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 Mitsumi Standard Interface
The syntax for this CD-ROM interface is:
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mcd=iobase,[irq[,wait_value]]
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 (`mcdx=')
At present this `experimental' driver has a setup func-
tion, but no parameters are implemented yet (as of
1.3.15). This is for the same hardware as above, but the
driver has extended features.
The Optics Storage Interface
The syntax for this type of card is:
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 val-
ues, 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.
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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_2,...param_8]],name
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:
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 implementa-
tion of the param_n values where used. Interested readers
should refer to the section in that document on their par-
ticular card.
The Floppy Disk Driver
There are many floppy driver options, and they are all
listed in README.fd in linux/drivers/block. This informa-
tion is taken directly from that file.
floppy=mask,allowed_drive_mask
Sets the bitmask of allowed drives to mask. By default,
only units 0 and 1 of each floppy controller are allowed.
This is done because certain non-standard hardware (ASUS
PCI motherboards) mess up the keyboard when accessing
units 2 or 3. This option is somewhat obsoleted by the
cmos option.
floppy=all_drives
Sets the bitmask 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 bitmask to allow only units 0 and 1. (The
default)
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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 con-
troller (default)
floppy=two_fdc or floppy=address,two_fdc
Tells the floppy driver that you have two floppy con-
trollers. 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 convention 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 bitmask. This is useful if you
have more than two floppy drives (only two can be
described in the physical cmos), or if your BIOS uses non-
standard CMOS types. Setting the CMOS to 0 for the first
two drives (default) makes the floppy driver read the
physical cmos for those drives.
floppy=unexpected_interrupts
Print a warning message when an unexpected interrupt is
received (default behaviour)
floppy=no_unexpected_interrupts or floppy=L40SX
Don't print a message when an unexpected interrupt is
received. This is needed on IBM L40SX laptops in certain
video modes. (There seems to be an interaction between
video and floppy. The unexpected interrupts only affect
performance, and can safely be ignored.)
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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 Readme.Linux file,
in linux/drivers/sound. It accepts a boot arg of the form:
sound=device1[,device2[,device3...[,device11]]]
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.
The Bus Mouse Driver (`bmouse=')
The busmouse driver only accepts one parameter, that being
the hardware IRQ value to be used.
AUTHORS
Linus Torvalds (and many others)
SEE ALSO
klogd(8), lilo.conf(5), lilo(8), mount(8), rdev(8)
This man page has been derived from the Boot Parameter
HOWTO (version 1.0.1) written by Paul Gortmaker. Slightly
more information may be found in this (or a more recent)
HOWTO.
Linux 1.3.19 15 August 1995 15