bootparam(7) manual page

Table of Contents

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.\» This man page written 950814 by aeb, based on Paul Gortmaker's HOWTO.\» (dated v1.0.1, 15/08/95).
.\"
.TH BOOTPARAM 7 «15 August 1995» «Linux 1.3.19» «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 tosupply the kernel with information about hardware parameters thatthe kernel would not be able to determine on its own, or to avoid/overridethe values that the kernel would otherwise detect.

When the kernel is booted directly by the BIOS (say from a floppy to

which you copied a kernel using `cp zImage /dev/fd0'),you have no opportunity to specify any parameters.

So, in order to take advantage of this possibility you have to

use software that is able to pass parameters, like LILO or loadlin.

For a few parameters one can also modify the kernel image itself,

using rdev, see
.BR rdev (8)
for further details.

The LILO program (LInux LOader) written by Werner Almesberger is the

most commonly used. It has the ability to boot various kernels, andstores 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, 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 DOSprompt (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. Acommon example is `SoundBlaster Compatible' sound cards that requirethe DOS driver to twiddle a few mystical registers to put the cardinto a SB compatible mode. Booting DOS with the supplied driver, andthen loading Linux from the DOS prompt with loadlin avoids the resetof the card that happens if one rebooted instead.

.SH THE ARGUMENT LIST

Most of the boot args take the form of:

.IP
name[=value_1][,value_2]...[,value_11]
.LP
where `name' is a unique keyword that is used to identify what part ofthe kernel the associated values (if any) are to be given to. Multipleboot args are just a space separated list of the above format. Notethe limit of 11 is real, as the present code only handles 11 commaseparated parameters per keyword. (However, you can re-use the samekeyword with up to an additional 11 parameters in unusuallycomplicated 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 isdescribed 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') hasbeen associated with a setup function (`foo_setup()') for a particulardevice or part of the kernel. If you passed the kernel the linefoo=3,4,5,6 then the kernel would search the bootsetups array to seeif `foo' was registered. If it was, then it would call the setupfunction associated with `foo' (foo_setup()) and hand it the arguments3, 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 tobe set. A (useless?) example would be to use `TERM=vt100' as a bootargument.

Any remaining arguments that were not picked up by the kernel and were

not interpreted as environment variables are then passed onto processone, which is usually the init program. The most common argument thatis passed to the init process is the word `single' which instructs initto boot the computer in single user mode, and not launch all the usualdaemons. Check the manual page for the version of init installed onyour system to see what arguments it accepts.

.SH «GENERAL NON-DEVICE SPECIFIC BOOT ARGS"

.SS «`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 wouldcause solid lockups while performing floating point calculations.

Using the `no387' boot arg causes Linux to ignore the maths

coprocessor even if you have one. Of course you must then have yourkernel compiled with math emulation support!

.SS «`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 modeafter 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 chipsto use Linux.

.SS «`root=...'"

This argument tells the kernel what device is to be used as the root

filesystem while booting. The default of this setting is determinedat compile time, and usually is the value of the root device of thesystem that the kernel was built on. To override this value, andselect the second floppy drive as the root device, one woulduse `root=/dev/fd1'. (The root device can also be set using.BR rdev (8).)

The root device can be specified symbolically or numerically.

A symbolic specification has the form /dev/XXYN, where XX designates

the device type (`hd' for ST-506 compatible hard disk, with Y in`a'-`h'; `sd' for SCSI compatible disk, with Y in `a'-`e'; `xd'for XT compatible disk, with Y either `a' or `b'; `fd' forfloppy disk, with Y the floppy drive number - fd0 would bethe DOS `A:' drive, and fd1 would be `B:'), Y the driver letter ornumber, 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 analternative.)

.SS «`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 canwrite 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
.BR 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

.BR rdev (8).

.SS «`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 <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 alsoprint the messages of DEBUG priority.

The console loglevel can also be set at run time via an option

to klogd. See
.BR klogd (8).

.SS «`reserve=...'"

This is used to protect I/O port regions from probes. The form of the

command is:
.IP
.BI reserve= iobase,extent[,iobase,extent]...
.LP

In some machines it may be necessary to prevent device drivers from

checking for devices (auto-probing) in a specific region. This may bebecause of hardware that reacts badly to the probing, or hardwarethat would be mistakenly identified, or merelyhardware 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

.IP
reserve=0x300,32 blah=0x300
.LP
keeps all device drivers except the driver for `blah' from probing0x300-0x31f.

.SS «`ramdisk=...'

This 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 floppyloaded into the RAM disk device, they would use:.IP
ramdisk=1440
.LP

This option is set at compile time (default: no RAM disk),

and can be modified using
.BR rdev (8).

.SS «`mem=...'"

The BIOS call defined in the PC specification that returns

the amount of installed memory was only designed to be ableto report up to 64MB. Linux uses this BIOS call at boot todetermine how much memory is installed. If you have more than 64MB of

RAM installed, you can use this boot arg to tell Linux how much memory

you have. The value is in decimal or hexadecimal (prefix 0x),and the suffixes `k' (times 1024) or `M' (times 1048576) can be used.

Here is a quote from Linus on usage of the `mem=' parameter.

\&``The kernel will accept any `mem=xx' parameter you give it, and if itturns 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 a96MB 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 full96MB addressable. The reverse is also true: some chipsets will mapthe physical memory that is covered by the BIOS area into the areajust 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 thanit actually does have, bad things will happen: maybe not at once, butsurely eventually.''

.SH «BOOT ARGUMENTS FOR SCSI DEVICES"

General notation for this section:

.I iobase
-- the first I/O port that the SCSI host occupies. These arespecified in hexidecimal notation, and usually lie in the range from0x200 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 usuallyused for common peripherals like IDE hard disks, floppies, serialports, etc.

.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 valueis 7, but the Seagate and Future Domain TMC-950 boards use 6.

.I parity
-- whether the SCSI host adapter expects the attached devicesto supply a parity value with all information exchanges. Specifying aone indicates parity checking is enabled, and a zero disables paritychecking. Again, not all adapters will support selection of paritybehaviour as a boot argument.

.SS «`max_scsi_luns=...'"

A SCSI device can have a number of `sub-devices' contained within

itself. The most common example is one of the new SCSI CD-ROMs thathandle more than one disk at a time. Each CD is addressed as a`Logical Unit Number' (LUN) of that particular device. But mostdevices, 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 andeight. To avoid problems as described above, one would use n=1 toavoid upsetting such broken devices.

.SS «SCSI tape configuration"

Some boot time configuration of the SCSI tape driver can be achieved

by using the following:
.IP
.BI st= buf_size[,write_threshold[,max_bufs]]
.LP

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 aridiculous 16384kB. The
.I write_threshold
is the value at which the buffer is committed to tape, with adefault value of 30kB. The maximum number of buffers varieswith the number of drives detected, and has a default of two.

An example usage would be:

.IP
st=32,30,2
.LP

Full details can be found in the README.st file that is in the scsi

directory of the kernel source tree.

.SS «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 willhave to use a boot arg of the form:
.IP
.BI aha152x= iobase[,irq[,scsi-id[,reconnect[,parity]]]].LP

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 non-zero valueis used. An example usage is as follows:
.IP
aha152x=0x340,11,7,1
.LP

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 aniobase, irq, scsi-id and reconnect value as well.

.SS «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 sharethe bus with other devices. The boot arg looks like the following..IP
.BI aha1542= iobase[,buson,busoff[,dmaspeed]]
.LP

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 thecard dominates the ISA bus. The defaults are 11us on, and 4us off, sothat other cards (such as an ISA LANCE Ethernet card) have a chance toget 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 to10MB/s assuming that your motherboard is capable of handling it.

Experiment with caution if using values over 5MB/s.

.SS «Adaptec aha274x, aha284x, aic7xxx configuration"

These boards can accept an argument of the form:

.IP
.BI aic7xxx= extended,no_reset
.LP

The

.I extended
value, if non-zero, indicates that extended translation for largedisks is enabled. The
.I no_reset
value, if non-zero, tells the driver not to reset the SCSI bus whensetting up the host adaptor at boot.

.SS «BusLogic SCSI Hosts configuration (`buslogic=')"

At present, the buslogic driver accepts only one parameter, that being

the I/O base. It expects that to be one of the following valid values:0x130, 0x134, 0x230, 0x234, 0x330, 0x334.

.SS «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:.IP
.BI tmc8xx= mem_base,irq
.LP

The

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

.SS «Pro Audio Spectrum configuration"

The PAS16 uses a NC5380 SCSI chip, and newer models support

jumperless configuration. The boot arg is of the form:.IP
.BI pas16= iobase,irq
.LP

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 aperformance loss. The iobase is usually 0x388.

.SS «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:.IP
.BI st0x= mem_base,irq
.LP

The

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

.SS «Trantor T128 configuration"

These cards are also based on the NCR5380 chip, and accept the

following options:
.IP
.BI t128= mem_base,irq
.LP

The valid values for

.I mem_base
are as follows: 0xcc000, 0xc8000, 0xdc000, 0xd8000.

.SS «Cards that don't Accept Boot Args"

At present, the following SCSI cards do not make use of any boot-time

parameters. In some cases, you can hard-wire values by directlyediting 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.

.SH «HARD DISKS"

.SS «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. Drivespecific 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 optionwill 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.

.SS «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 valueis ignored for IDE disks. The IRQ value specified will be the IRQused for the interface that the drive resides on, and is not really adrive specific parameter.

.SS «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 asdrives on the primary interface, it will corrupt your data. Using thisoption tells the driver to make sure that both interfaces are neverused at the same time.

.SS «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.

.SS «The `hd=noprobe' option"

Do not probe for this drive. For example,

.IP
hdb=noprobe hdb=1166,7,17
.LP
would disable the probe, but still specify the drive geometry sothat it would be registered as a valid block device, and henceuseable.

.SS «The `hd=nowerr' option"

Some drives apparently have the WRERR_STAT bit stuck on permanently.

This enables a work-around for these broken devices.

.SS «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-ROMis identified automatically, but if it isn't then this may help.

.SS «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 threevalues (C/H/S) -- any more or any less and it will silently ignoreyou. Also, it only accepts `hd=' as an argument, i.e. `hda='and so on are not valid here. The format is as follows:.IP
hd=cyls,heads,sects
.LP

If there are two disks installed, the above is repeated with the

geometry parameters of the second disk.

.SS «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:

.IP
xd=type,irq,iobase,dma_chan
.LP

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 fromthe same manufacturer is the BIOS string used for detection, which isnot 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 disappoint it. Here is anexample usage for a WD1002 controller with the BIOS disabled/removed,using the `default' XT controller parameters:.IP
xd=2,5,0x320,3
.LP

.SH «CD-ROMs (Non-SCSI/ATAPI/IDE)"

.SS «The Aztech Interface"

The syntax for this type of card is:

.IP
aztcd=iobase[,magic_number]
.LP

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 valuesare ignored.

.SS «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 asfollows:
.IP
cdu31a=iobase,[irq[,is_pas_card]]
.LP

Specifying an IRQ value of zero tells the driver that hardware

interrupts aren't supported (as on some PAS cards). If your cardsupports interrupts, you should use them as it cuts down on the CPUusage 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.

.SS «The CDU-535 Sony Interface"

The syntax for this CD-ROM interface is:

.IP
sonycd535=iobase[,irq]
.LP

A zero can be used for the I/O base as a `placeholder' if one wishes

to specify an IRQ value.

.SS «The GoldStar Interface"

The syntax for this CD-ROM interface is:

.IP
gscd=iobase
.LP

.SS «The Mitsumi Standard Interface"

The syntax for this CD-ROM interface is:

.IP
mcd=iobase,[irq[,wait_value]]
.LP

The

.I wait_value
is used as an internal timeout value for people who arehaving problems with their drive, and may or may not be implementeddepending on a compile time #define.

.SS «The Mitsumi XA/MultiSession Interface (`mcdx=')"

At present this `experimental' driver has a setup function, but no

parameters are implemented yet (as of 1.3.15). This is for the samehardware as above, but the driver has extended features.

.SS «The Optics Storage Interface"

The syntax for this type of card is:

.IP
optcd=iobase
.LP

.SS «The Phillips CM206 Interface"

The syntax for this type of card is:

.IP
cm206=[iobase][,irq]
.LP

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 enableautoprobing.

.SS «The Sanyo Interface"

The syntax for this type of card is:

.IP
sjcd=iobase[,irq[,dma_channel]]
.LP

.SS «The SoundBlaster Pro Interface"

The syntax for this type of card is:

.IP
sbpcd=iobase,type
.LP
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.

.SH «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 itsmost generic form, it looks something like this:.IP
ether=irq,iobase[,param_1[,param_2,...param_8]],name.LP

The first non-numeric argument is taken as the name. The param_n

values (if applicable) usually have different meanings for eachdifferent card/driver. Typical param_n values are used to specifythings like shared memory address, interface selection, DMA channeland 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 beaccomplished with a simple:
.IP
ether=0,0,eth1
.LP

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 implementationof the param_n values where used. Interested readers should refer tothe section in that document on their particular card.

.SH «The Floppy Disk Driver"

There are many floppy driver options, and they are all listed in

README.fd in linux/drivers/block. This information is taken directly

from that file.

.SS «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 becausecertain non-standard hardware (ASUS PCI motherboards) mess up thekeyboard when accessing units 2 or 3. This option is somewhatobsoleted by the cmos option.

.SS «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.

.SS «floppy=asus_pci"

Sets the bitmask to allow only units 0 and 1. (The default)

.SS «floppy=daring"

Tells the floppy driver that you have a well behaved floppy

controller. This allows more efficient and smoother operation, butmay fail on certain controllers. This may speed up certain operations.

.SS «floppy=0,daring"

Tells the floppy driver that your floppy controller should be used

with caution.

.SS «floppy=one_fdc"

Tells the floppy driver that you have only floppy controller (default)

.SS «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 isnot given, 0x370 is assumed.

.SS «floppy=thinkpad"

Tells the floppy driver that you have a Thinkpad. Thinkpads use an

inverted convention for the disk change line.

.SS «floppy=0,thinkpad"

Tells the floppy driver that you don't have a Thinkpad.

.SS «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 twofloppy drives (only two can be described in the physical cmos), or ifyour BIOS uses non-standard CMOS types. Setting the CMOS to 0 for thefirst two drives (default) makes the floppy driver read the physicalcmos for those drives.

.SS «floppy=unexpected_interrupts"

Print a warning message when an unexpected interrupt is received

(default behaviour)

.SS «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 tobe an interaction between video and floppy. The unexpected interruptsonly affect performance, and can safely be ignored.)

.SH «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 isdescribed in the Readme.Linux file, in linux/drivers/sound. It acceptsa boot arg of the form:
.IP
sound=device1[,device2[,device3...[,device11]]]
.LP
where each deviceN value is of the following format 0xTaaaId and thebytes are used as follows: