boot.7: tfix

[thirdparty/man-pages.git] / man7 / bootparam.7

.\" Copyright (c) 1995,1997 Paul Gortmaker and Andries Brouwer
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.\" This man page written 950814 by aeb, based on Paul Gortmaker's HOWTO
.\" (dated v1.0.1, 15/08/95).
.\" Major update, aeb, 970114.
.\"
.TH BOOTPARAM 7 2014-06-13 "Linux" "Linux Programmer's Manual"
.SH NAME
bootparam \- introduction to boot time parameters of the Linux kernel
.SH 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 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
.\" .BR lilo (8)
.\" and
.\" .BR 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.
.SS 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:

.in +4n
.nf
name[=value_1][,value_2]...[,value_10]
.fi
.in
.LP
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
.IR 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
.BR init (1)
program.
The most common argument that
is passed to the
.I 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
.BR init (1)
installed on
your system to see what arguments it accepts.
.SS General non-device-specific boot arguments
.TP
.B "'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
.IR /sbin/init ,
then
.IR /etc/init ,
then
.IR /bin/init ,
then
.I /bin/sh
and panic if all of this fails.
.TP
.B "'nfsaddrs=...'"
This sets the nfs boot address to the given string.
This boot address is used in case of a net boot.
.TP
.B "'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.
.TP
.B  "'no387'"
(Only when
.B 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 argument 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!
.TP
.B "'no-hlt'"
(Only when
.B 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.
.TP
.B "'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 be specified symbolically or numerically.
A symbolic specification has the form
.IR /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\(emfd0 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 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,
.I /dev/sda3
is major 8, minor 3, so you could use 'root=0x803' as an
alternative.)
.TP
.BR "'rootdelay='"
This parameter sets the delay (in seconds) to pause before attempting
to mount the root filesystem.
.TP
.BR "'rootflags=...'"
This parameter sets the mount option string for the root filesystem
(see also
.BR fstab (5)).
.TP
.BR "'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 alternate media.
.TP
.BR '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
.BR mount (8).)

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

.TP
.B "'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:

.in +4n
.nf
resume=/dev/hda2
.fi
.in
.TP
.B "'reserve=...'"
This is used to protect I/O port regions from probes.
The form of the command is:

.in +4n
.nf
.BI reserve= iobase,extent[,iobase,extent]...
.fi
.in
.sp
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

.in +4n
.nf
reserve=0x300,32  blah=0x300
.fi
.in
.IP
keeps all device drivers except the driver for 'blah' from probing
0x300\-0x31f.
.TP
.B "'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.

.in +0.5i
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'.

.BR 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.
.in

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.
.TP
.B "'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

.in +4n
.nf
echo N > /proc/sys/kernel/panic
.fi
.in
.TP
.B "'reboot=[warm|cold][,[bios|hard]]'"
(Only when
.B 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.
.TP
.BR 'nosmp' " and " 'maxcpus=N'
(Only when __SMP__ is defined.)
A command-line option of 'nosmp' or 'maxcpus=0' will disable SMP
activation entirely; an option 'maxcpus=N' limits the maximum number
of CPUs activated in SMP mode to N.
.SS Boot arguments for use by kernel developers
.TP
.B "'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
.I console_loglevel
are also printed on the console.
(For these levels, see
.IR <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
.BR klogd (8).
.TP
.B "'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
.I prof_shift
to a nonzero value.
This is done either by specifying
.B CONFIG_PROFILE
at compile time, or by giving the 'profile=' option.
Now the value that
.I prof_shift
gets will be N, when given, or
.BR 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:

.in +4n
.nf
profile[address >> prof_shift]++;
.fi
.in
.sp
The raw profiling information can be read from
.IR /proc/profile .
Probably you'll want to use a tool such as readprofile.c to digest it.
Writing to
.I /proc/profile
will clear the counters.
.TP
.B "'swap=N1,N2,N3,N4,N5,N6,N7,N8'"
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.
.TP
.B "'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.
.SS Boot arguments for ramdisk use
(Only if the kernel was compiled with
.BR CONFIG_BLK_DEV_RAM .)
In general it is a bad idea to use a ramdisk under Linux\(emthe
system will use available memory more efficiently itself.
But while booting (or while constructing boot floppies)
it is often useful to load the floppy contents into a
ramdisk.
One might also have a system in which first
some modules (for filesystem or hardware) must be loaded
before the main disk can be accessed.

In Linux 1.3.48, ramdisk handling was changed drastically.
Earlier, the memory was allocated statically, and there was
a 'ramdisk=N' parameter to tell its size.
(This could also be set in the kernel image at compile time.)
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
.IR Documentation/blockdev/ramdisk.txt
.RI ( Documentation/ramdisk.txt
in older kernels).

There are four parameters, two boolean and two integral.
.TP
.B "'load_ramdisk=N'"
If N=1, do load a ramdisk.
If N=0, do not load a ramdisk.
(This is the default.)
.TP
.B "'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.)
.TP
.BR 'ramdisk_size=N' " or (obsolete) " 'ramdisk=N'
Set the maximal size of the ramdisk(s) to N kB.
The default is 4096 (4 MB).
.TP
.B "'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.
.TP
.B "'noinitrd'"
(Only if the kernel was compiled with
.B CONFIG_BLK_DEV_RAM
and
.BR 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
.I /linuxrc
is executed; afterward the "real" root filesystem is mounted,
and the initrd filesystem is moved over to
.IR /initrd ;
finally
the usual boot sequence (e.g., invocation of
.IR /sbin/init )
is performed.

For a detailed description of the initrd feature, see the kernel source file
.IR 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
.IR /dev/initrd .
(This device can be used only once: the data is freed as soon as
the last process that used it has closed
.IR /dev/initrd .)
.SS Boot arguments for SCSI devices
General notation for this section:

.I 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.

.I 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.

.I 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.

.I parity
-- whether the SCSI host adapter expects the attached devices
to supply a parity value with all information exchanges.
Specifying a one indicates parity checking is enabled,
and a zero disables parity checking.
Again, not all adapters will support selection of parity
behavior as a boot argument.
.TP
.B "'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
.B CONFIG_SCSI_MULTI_LUN
is not set, newer kernels will by default probe only 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.
.TP
.B "SCSI tape configuration"
Some boot time configuration of the SCSI tape driver can be achieved
by using the following:

.in +4n
.nf
.BI st= buf_size[,write_threshold[,max_bufs]]
.fi
.in
.sp
The first two numbers are specified in units of kB.
The default
.I buf_size
is 32kB, and the maximum size that can be specified is a
ridiculous 16384kB.
The
.I 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:

.in +4n
.nf
st=32,30,2
.fi
.in
.IP
Full details can be found in the file
.I Documentation/scsi/st.txt
(or
.I drivers/scsi/README.st
for older kernels) in the Linux kernel source.
.TP
.B "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 argument of the form:

.in +4n
.nf
.BI aha152x= iobase[,irq[,scsi-id[,reconnect[,parity]]]]
.fi
.in
.IP
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
.I reconnect
value will allow device disconnect/reconnect if a nonzero value
is used.
An example usage is as follows:

.in +4n
.nf
aha152x=0x340,11,7,1
.fi
.in
.IP
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.
.TP
.B "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.

.in +4n
.nf
.BI aha1542= iobase[,buson,busoff[,dmaspeed]]
.fi
.in
.IP
Valid iobase values are usually one of: 0x130, 0x134, 0x230, 0x234,
0x330, 0x334.
Clone cards may permit other values.

The
.IR 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
.I dmaspeed
value refers to the rate (in MB/s) at which the DMA
(Direct Memory Access) transfers proceed.
The default is 5MB/s.
Newer revision cards allow you to select this value as part of the
soft-configuration, older cards use jumpers.
You can use values up to
10MB/s assuming that your motherboard is capable of handling it.
Experiment with caution if using values over 5MB/s.
.TP
.B "Adaptec aha274x, aha284x, aic7xxx configuration"
These boards can accept an argument of the form:

.in +4n
.nf
.BI aic7xxx= extended,no_reset
.fi
.in
.IP
The
.I extended
value, if nonzero, indicates that extended translation for large
disks is enabled.
The
.I no_reset
value, if nonzero, tells the driver not to reset the SCSI bus when
setting up the host adapter at boot.
.TP
.B "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 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.
.TP
.B "AM53C974"
Syntax:

.in +4n
.nf
.BI AM53C974= host-scsi-id,target-scsi-id,max-rate,max-offset
.fi
.in
.TP
.B "BusLogic SCSI Hosts configuration ('BusLogic=')"

Syntax:
.in +4n
.nf
.BI BusLogic= N1,N2,N3,N4,N5,S1,S2,...
.fi
.in
.IP
For an extensive discussion of the BusLogic command line parameters,
see the kernel source file
.IR 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).
.TP
.B "EATA/DMA configuration"
The default list of I/O ports to be probed can be changed by

.in +4n
.nf
.BI eata= iobase,iobase,... .
.fi
.in
.TP
.B "Future Domain TMC-16x0 configuration"
Syntax:

.in +4n
.nf
.BI fdomain= iobase,irq[,adapter_id]
.fi
.in
.TP
.B "Great Valley Products (GVP) SCSI controller configuration"
Syntax:

.in +4n
.nf
.BI gvp11= dma_transfer_bitmask
.fi
.in
.TP
.B "Future Domain TMC-8xx, TMC-950 configuration"
Syntax:

.in +4n
.nf
.BI tmc8xx= mem_base,irq
.fi
.in
.IP
The
.I 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.
.TP
.B "IN2000 configuration"
Syntax:

.in +4n
.nf
.BI in2000= S
.fi
.in
.IP
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
.IR drivers/scsi/in2000.c .
.TP
.B "NCR5380 and NCR53C400 configuration"
The boot argument is of the form

.in +4n
.nf
.BI ncr5380= iobase,irq,dma
.fi
.in
.IP
or

.in +4n
.nf
.BI ncr53c400= iobase,irq
.fi
.in
.IP
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
.I Documentation/scsi/g_NCR5380.txt
(or
.I drivers/scsi/README.g_NCR5380
for older kernels) in the Linux kernel source.
.TP
.B "NCR53C8xx configuration"
Syntax:

.in +4n
.nf
.BI ncr53c8xx= S
.fi
.in
.IP
where S is a comma-separated string of items keyword:value.
Recognized keywords are: mpar (master_parity), spar (scsi_parity),
disc (disconnection), specf (special_features), ultra (ultra_scsi),
fsn (force_sync_nego), tags (default_tags), sync (default_sync),
verb (verbose), debug (debug), burst (burst_max).
For the function of the assigned values, see the kernel source file
.IR drivers/scsi/ncr53c8xx.c .
.TP
.B "NCR53c406a configuration"
Syntax:

.in +4n
.nf
.BI ncr53c406a= iobase[,irq[,fastpio]]
.fi
.in
.IP
Specify irq = 0 for noninterrupt driven mode.
Set fastpio = 1 for fast pio mode, 0 for slow mode.
.TP
.B "Pro Audio Spectrum configuration"
The PAS16 uses a NC5380 SCSI chip, and newer models support
jumperless configuration.
The boot argument is of the form:

.in +4n
.nf
.BI pas16= iobase,irq
.fi
.in
.IP
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.
.TP
.B "Seagate ST-0x configuration"
If your card is not detected at boot time,
you will then have to use a boot argument of the form:

.in +4n
.nf
.BI st0x= mem_base,irq
.fi
.in
.IP
The
.I 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.
.TP
.B "Trantor T128 configuration"
These cards are also based on the NCR5380 chip, and accept the
following options:

.in +4n
.nf
.BI t128= mem_base,irq
.fi
.in
.IP
The valid values for
.I mem_base
are as follows: 0xcc000, 0xc8000, 0xdc000, 0xd8000.
.TP
.B "UltraStor 14F/34F configuration"
The default list of I/O ports to be probed can be changed by

.in +4n
.nf
.BI eata= iobase,iobase,... .
.fi
.in
.TP
.B "WD7000 configuration"
Syntax:

.in +4n
.nf
.BI wd7000= irq,dma,iobase
.fi
.in
.TP
.B "Commodore Amiga A2091/590 SCSI controller configuration"
Syntax:

.in +4n
.nf
.BI wd33c93= S
.fi
.in
.IP
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 the kernel source file
.IR drivers/scsi/wd33c93.c .
.SS Hard disks
.TP
.B "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
.I Documentation/ide.txt
(or
.I drivers/block/README.ide
for older kernels) in the Linux kernel source for more details.
.TP
.B "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.
.TP
.B "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.
.TP
.B "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.
.TP
.B "The 'hd=noprobe' option"
Do not probe for this drive.
For example,

.in +4n
.nf
hdb=noprobe hdb=1166,7,17
.fi
.in
.IP
would disable the probe, but still specify the drive geometry so
that it would be registered as a valid block device, and hence
usable.
.TP
.B "The 'hd=nowerr' option"
Some drives apparently have the
.B WRERR_STAT
bit stuck on permanently.
This enables a work-around for these broken devices.
.TP
.B "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.
.TP
.B "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 argument, that is, 'hda='
and so on are not valid here.
The format is as follows:

.in +4n
.nf
hd=cyls,heads,sects
.fi
.in
.IP
If there are two disks installed, the above is repeated with the
geometry parameters of the second disk.
.TP
.B "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:

.in +4n
.nf
xd=type,irq,iobase,dma_chan
.fi
.in
.IP
The type value specifies the particular manufacturer of the card,
overriding autodetection.
For the types to use, consult the
.I drivers/block/xd.c
source file of the kernel you are using.
The type is an index in the list
.I xd_sigs
and in the course of time
.\" 1.1.50, 1.3.81, 1.3.99, 2.0.34, 2.1.67, 2.1.78, 2.1.127
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:

.in +4n
.nf
xd=2,5,0x320,3
.fi
.in
.TP
.B "Syquest's EZ* removable disks"
Syntax:

.in +4n
.nf
.BI ez= iobase[,irq[,rep[,nybble]]]
.fi
.in
.SS IBM MCA bus devices
See also the kernel source file
.IR Documentation/mca.txt .
.TP
.B "PS/2 ESDI hard disks"
It is possible to specify the desired geometry at boot time:

.in +4n
.nf
.BI ed= cyls,heads,sectors.
.fi
.in
.IP
For a ThinkPad-720, add the option

.in +4n
.nf
.BR tp720=1 .
.fi
.in
.TP
.B "IBM Microchannel SCSI Subsystem configuration"
Syntax:

.in +4n
.nf
.BI ibmmcascsi= N
.fi
.in
.IP
where N is the
.I pun
(SCSI ID) of the subsystem.
.TP
.B "The Aztech Interface"
The syntax for this type of card is:

.in +4n
.nf
aztcd=iobase[,magic_number]
.fi
.in
.IP
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.
.TP
.B "Parallel port CD-ROM drives"
Syntax:

.in +4n
.nf
pcd.driveN=prt,pro,uni,mod,slv,dly
pcd.nice=nice
.fi
.in
.IP
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.
.TP
.B "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:

.in +4n
.nf
cdu31a=iobase,[irq[,is_pas_card]]
.fi
.in
.IP
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
.I is_pas_card
should be entered as 'PAS' if using a Pro Audio Spectrum card,
and otherwise it should not be specified at all.
.TP
.B "The CDU-535 Sony Interface"
The syntax for this CD-ROM interface is:

.in +4n
.nf
sonycd535=iobase[,irq]
.fi
.in
.IP
A zero can be used for the I/O base as a 'placeholder' if one wishes
to specify an IRQ value.
.TP
.B "The GoldStar Interface"
The syntax for this CD-ROM interface is:

.in +4n
.nf
gscd=iobase
.fi
.in
.TP
.B "The ISP16 CD-ROM Interface"
Syntax:

.in +4n
.nf
isp16=[iobase[,irq[,dma[,type]]]]
.fi
.in
.IP
(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'.
.TP
.B "The Mitsumi Standard Interface"
The syntax for this CD-ROM interface is:

.in +4n
.nf
mcd=iobase,[irq[,wait_value]]
.fi
.in
.IP
The
.I 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.
.TP
.B "The Mitsumi XA/MultiSession Interface"
This is for the same hardware as above, but the driver has extended features.
Syntax:

.in +4n
.nf
mcdx=iobase[,irq]
.fi
.in
.TP
.B "The Optics Storage Interface"
The syntax for this type of card is:

.in +4n
.nf
optcd=iobase
.fi
.in
.TP
.B "The Phillips CM206 Interface"
The syntax for this type of card is:

.in +4n
.nf
cm206=[iobase][,irq]
.fi
.in
.IP
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.
.TP
.B "The Sanyo Interface"
The syntax for this type of card is:

.in +4n
.nf
sjcd=iobase[,irq[,dma_channel]]
.fi
.in
.TP
.B "The SoundBlaster Pro Interface"
The syntax for this type of card is:

.in +4n
.nf
sbpcd=iobase,type
.fi
.in
.IP
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.
.SS 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:

.in +4n
.nf
ether=irq,iobase[,param_1[,...param_8]],name
.fi
.in

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:

.in +4n
.nf
ether=0,0,eth1
.fi
.in

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.
.SS The floppy disk driver
There are many floppy driver options, and they are all listed in
.I Documentation/floppy.txt
(or
.I drivers/block/README.fd
for older kernels) in the Linux kernel source.
This information is taken directly
from that file.
.TP
.B "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 hardware (ASUS PCI motherboards) mess up the
keyboard when accessing units 2 or 3.
This option is somewhat
obsoleted by the cmos option.
.TP
.B "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.
.TP
.B "floppy=asus_pci"
Sets the bit mask to allow only units 0 and 1.
(The default)
.TP
.B "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.
.TP
.B "floppy=0,daring"
Tells the floppy driver that your floppy controller should be used
with caution.
.TP
.B "floppy=one_fdc"
Tells the floppy driver that you have only floppy controller (default)
.TP
.BR 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.
.TP
.B "floppy=thinkpad"
Tells the floppy driver that you have a Thinkpad.
Thinkpads use an
inverted convention for the disk change line.
.TP
.B "floppy=0,thinkpad"
Tells the floppy driver that you don't have a Thinkpad.
.TP
.B "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.
Setting the CMOS to 0 for the
first two drives (default) makes the floppy driver read the physical
cmos for those drives.
.TP
.B "floppy=unexpected_interrupts"
Print a warning message when an unexpected interrupt is received
(default behavior)
.TP
.BR 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.)
.SS 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
.IR Documentation/sound/oss/README.OSS
.RI ( drivers/sound/Readme.linux
in older kernel versions).
It accepts
a boot argument of the form:

.in +4n
.nf
sound=device1[,device2[,device3...[,device10]]]
.fi
.in
.IP
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.
.SS ISDN drivers
.TP
.B "The ICN ISDN driver"
Syntax:

.in +4n
.nf
icn=iobase,membase,icn_id1,icn_id2
.fi
.in
.IP
where icn_id1,icn_id2 are two strings used to identify the
card in kernel messages.
.TP
.B "The PCBIT ISDN driver"
Syntax:

.in +4n
.nf
pcbit=membase1,irq1[,membase2,irq2]
.fi
.in
.IP
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.
.TP
.B "The Teles ISDN driver"
Syntax:

.in +4n
.nf
teles=iobase,irq,membase,protocol,teles_id
.fi
.in
.IP
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.
.SS Serial port drivers
.TP
.B "The RISCom/8 Multiport Serial Driver ('riscom8=')"
Syntax:

.in +4n
.nf
riscom=iobase1[,iobase2[,iobase3[,iobase4]]]
.fi
.in
.IP
More details can be found in the kernel source file
.IR Documentation/riscom8.txt .
.TP
.B "The DigiBoard Driver ('digi=')"
If this option is used, it should have precisely six parameters.
Syntax:

.in +4n
.nf
digi=status,type,altpin,numports,iobase,membase
.fi
.in
.IP
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:

.in +4n
.nf
digi=E,PC/Xi,D,16,200,D0000
digi=1,0,0,16,0x200,851968
.fi
.in
.IP
More details can be found in the kernel source file
.IR Documentation/digiboard.txt .
.TP
.B "The Baycom Serial/Parallel Radio Modem"
Syntax:

.in +4n
.nf
baycom=iobase,irq,modem
.fi
.in
.IP
There are precisely 3 parameters; for several cards, give
several 'baycom=' commands.
The modem parameter is a string
that can take one of the values ser12, ser12*, par96, par96*.
Here the * denotes that software DCD is to be used, and
ser12/par96 chooses between the supported modem types.
For more details, see the file
.I Documentation/networking/baycom.txt
(or
.I drivers/net/README.baycom
for older kernels) in the Linux kernel source.
.TP
.B "Soundcard radio modem driver"
Syntax:

.in +4n
.nf
soundmodem=iobase,irq,dma[,dma2[,serio[,pario]]],0,mode
.fi
.in
.IP
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.
.SS The line printer driver
.TP
.B "'lp='"
.br
Syntax:

.in +4n
.nf
lp=0
lp=auto
lp=reset
lp=port[,port...]
.fi
.in
.IP
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.
.TP
.B "WDT500/501 driver"
Syntax:

.in +4n
.nf
wdt=io,irq
.fi
.in
.SS Mouse drivers
.TP
.B "'bmouse=irq'"
The busmouse driver accepts only one parameter, that being the
hardware IRQ value to be used.
.TP
.B "'msmouse=irq'"
And precisely the same is true for the msmouse driver.
.TP
.B "ATARI mouse setup"
Syntax:

.in +4n
.nf
atamouse=threshold[,y-threshold]
.fi
.in
.IP
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.
.SS Video hardware
.TP
.B "'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.
.\" .SH AUTHORS
.\" Linus Torvalds (and many others)
.SH SEE ALSO
.BR klogd (8),
.BR 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
.IR Documentation/kernel-parameters.txt .