bootparam

a b c d e f g h i j k l m n o p q r s t u v w x y z _

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

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

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

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

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

The other commonly used Linux loader is ‘LoadLin’ which is a DOS pro-
gram 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 com-
mon example is ‘SoundBlaster Compatible’ sound cards that require the
DOS driver to twiddle a few mystical registers to put the card into a
SB compatible mode. Booting DOS with the supplied driver, and then
loading Linux from the DOS prompt with loadlin avoids the reset of the
card that happens if one rebooted instead.

THE ARGUMENT LIST
The kernel command line is parsed into a list of strings (boot argu-
ments) separated by spaces. Most of the boot args take the form of:

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

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

Most of the sorting goes on in linux/init/main.c. First, the kernel
checks to see if the argument is any of the special arguments ‘root=’,
‘nfsroot=’, ‘nfsaddrs=’, ‘ro’, ‘rw’, ‘debug’ or ‘init’. The meaning
of these special arguments is described below.

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

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

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

GENERAL NON-DEVICE SPECIFIC BOOT ARGS
‘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 /etc/init, then
/bin/init, then /sbin/init, then /bin/sh and panic if all of this
fails.

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

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

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

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

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

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

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

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

‘ro’ and ‘rw’
The ‘ro’ option tells the kernel to mount the root 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).

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

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

In some machines it may be necessary to prevent device drivers from
checking for devices (auto-probing) in a specific region. This may be
because of hardware that reacts badly to the probing, or hardware that
would be mistakenly identified, or merely hardware you don’t want the
kernel to initialize.

The reserve boot-time argument specifies an I/O port region that
shouldn’t be probed. A device driver will not probe a reserved region,
unless another boot argument explicitly specifies that it do so.

For example, the boot line

reserve=0x300,32 blah=0x300

keeps all device drivers except the driver for ‘blah’ from probing
0x300-0x31f.

‘mem=...’
The BIOS call defined in the PC specification that returns the amount
of installed memory was 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 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.’’

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

‘panic=N’
By default the kernel will not reboot after a panic, but this option
will cause a kernel reboot after N seconds (if N > 0). This panic
timeout can also be set by "echo N > /proc/sys/kernel/panic".

‘reboot=[warm|cold][,[bios|hard]]’
(Only when CONFIG_BUGi386 is defined.) Since 2.0.22 a reboot is by
default a cold reboot. One asks for the old default with
‘reboot=warm’. (A cold reboot may be required to reset certain hard-
ware, but might destroy not yet written data in a disk cache. A warm
reboot may be faster.) By default a reboot is hard, by asking the
keyboard controller to pulse the reset line low, but there is at least
one type of motherboard where that doesn’t work. The option
‘reboot=bios’ will instead jump through the BIOS.

‘nosmp’ and ‘maxcpus=N’
(Only when __SMP__ is defined.) A command-line option of ‘nosmp’ or
‘maxcpus=0’ will disable SMP activation entirely; an option ‘maxc-
pus=N’ limits the maximum number of CPUs activated in SMP mode to N.

BOOT ARGUMENTS FOR USE BY KERNEL DEVELOPERS
‘debug’
Kernel messages are handed off to the kernel log daemon klogd so that
they may be logged to disk. Messages with a priority above con-
sole_loglevel are also printed on the console. (For these levels, see
<linux/kernel.h>.) By default this variable is set to log anything
more important than debug messages. This boot argument will cause the
kernel to also print the messages of DEBUG priority. The console
loglevel can also be set at run time via an option to klogd. See
klogd(8).

‘profile=N’
It is possible to enable a kernel profiling function, if one wishes to
find out where the kernel is spending its CPU cycles. Profiling is
enabled by setting the variable prof_shift to a nonzero value. This is
done either by specifying CONFIG_PROFILE at compile time, or by giving
the ‘profile=’ option. Now the value that prof_shift gets will be N,
when given, or CONFIG_PROFILE_SHIFT, when that is given, or 2, the
default. The significance of this variable is that it gives the
granularity of the profiling: each clock tick, if the system was exe-
cuting kernel code, a counter is incremented:

profile[address >> prof_shift]++;

The raw profiling information can be read from /proc/profile. Proba-
bly you’ll want to use a tool such as readprofile.c to digest it.
Writing to /proc/profile will clear the counters.

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

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

BOOT ARGUMENTS FOR RAMDISK USE
(Only if the kernel was compiled with CONFIG_BLK_DEV_RAM.) In general
it is a bad idea to use a ramdisk under Linux - the system will use
available memory more efficiently itself. But while booting (or while
constructing boot floppies) it is often useful to load the floppy con-
tents 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, or by use of rdev(8).) These days ram disks
use the buffer cache, and grow dynamically. For a lot of information
(e.g., how to use rdev(8) in conjunction with the new ramdisk setup),
see /usr/src/linux/Documentation/ramdisk.txt.

There are four parameters, two boolean and two integral.

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

‘prompt_ramdisk=N’
If N=1, do prompt for insertion of the floppy. (This is the default.)
If N=0, do not prompt. (Thus, this parameter is never needed.)

‘ramdisk_size=N’ or (obsolete) ‘ramdisk=N’
Set the maximal size of the ramdisk(s) to N kB. The default is 4096 (4
MB).

‘ramdisk_start=N’
Sets the starting block number (the offset on the floppy where the
ramdisk starts) to N. This is needed in case the ramdisk follows a
kernel image.

‘noinitrd’
(Only if the kernel was compiled with CONFIG_BLK_DEV_RAM and CON-
FIG_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 ini-
trd into a "normal" ramdisk, which is mounted read-write as root
device; then /linuxrc is executed; afterwards the "real" root file
system is mounted, and the initrd filesystem is moved over to /initrd;
finally the usual boot sequence (e.g. invocation of /sbin/init) is
performed.

For a detailed description of the initrd feature, see
/usr/src/linux/Documentation/initrd.txt.

The ‘noinitrd’ option tells the kernel that although it was compiled
for operation with initrd, it should not go through the above steps,
but leave the initrd data under /dev/initrd. (This device can be used
only once - the data is freed as soon as the last process that used it
has closed /dev/initrd.)

BOOT ARGUMENTS FOR SCSI DEVICES
General notation for this section:

iobase -- the first I/O port that the SCSI host occupies. These are
specified in 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 usu-
ally be 5, 7, 9, 10, 11, 12, and 15. The other values are usually used
for common peripherals like IDE hard disks, floppies, serial ports,
etc.

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

parity -- whether the SCSI host adapter expects the attached devices
to supply a parity value with all 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
behaviour as a boot argument.

‘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 that
handle more than one disk at a time. Each CD is addressed as a ‘Logi-
cal 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 CON-
FIG_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 maxi-
mum 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 configuration
The aha numbers refer to cards and the aic numbers refer to the actual
SCSI chip on these type of cards, including the Soundblaster-16 SCSI.

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

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

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

All the parameters are as described at the top of this section, and
the reconnect value will allow device disconnect/reconnect if a 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, meaning that if
you want to specify a parity setting, then you will have to specify an
iobase, irq, scsi-id and reconnect value as well.

Adaptec aha154x configuration
The aha1542 series cards have an i82077 floppy controller onboard,
while the aha1540 series cards do not. These are busmastering cards,
and have parameters to set the ‘‘fairness’’ that is used to share the
bus with other devices. The boot 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 microseconds that the
card dominates the ISA bus. The defaults are 11us on, and 4us off, so
that other cards (such as an ISA LANCE Ethernet card) have a chance to
get access to the ISA bus.

The dmaspeed value refers to the rate (in MB/s) at which the DMA
(Direct Memory Access) transfers proceed. The default is 5MB/s. Newer
revision cards allow you to select this value as part of the soft-con-
figuration, older cards use jumpers. You can use values up to 10MB/s
assuming that your motherboard is capable of handling it. Experiment
with caution if using values over 5MB/s.

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

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.

AdvanSys SCSI Hosts configuration (‘advansys=’)
The AdvanSys driver can accept up to four i/o addresses that will be
probed for an AdvanSys SCSI card. Note that these values (if used) do
not effect EISA or PCI probing in any way. They are only used for
probing ISA and VLB cards. In addition, if the driver has been com-
piled 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.

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

BusLogic SCSI Hosts configuration (‘BusLogic=’)
BusLogic=N1,N2,N3,N4,N5,S1,S2,...

For an extensive discussion of the BusLogic command line parameters,
see /usr/src/linux/drivers/scsi/BusLogic.c (lines 3149-3270 in the
kernel version I am looking at). The text below is a very much abbre-
viated 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 Queu-
ing. N3 is the Bus Settle Time in seconds. This is the amount of
time to wait between a Host Adapter Hard Reset which initiates a SCSI
Bus Reset and issuing any SCSI Commands. N4 is the Local Options (for
one Host Adapter). N5 is the Global Options (for all Host Adapters).

The string options are used to provide control over Tagged Queuing
(TQ:Default, TQ:Enable, TQ:Disable, TQ:<Per-Target-Spec>), over Error
Recovery (ER:Default, ER:HardReset, ER:BusDeviceReset, ER:None,
ER:<Per-Target-Spec>), and over Host Adapter Probing (NoProbe,
NoProbeISA, NoSortPCI).

EATA/DMA configuration
The default list of i/o ports to be probed can be changed by

eata=iobase,iobase,....

Future Domain TMC-16x0 configuration
fdomain=iobase,irq[,adapter_id]

Great Valley Products (GVP) SCSI controller configuration
gvp11=dma_transfer_bitmask

Future Domain TMC-8xx, TMC-950 configuration
tmc8xx=mem_base,irq

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

IN2000 configuration
in2000=S

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

NCR5380 and NCR53C400 configuration
The boot arg is of the form

ncr5380=iobase,irq,dma

ncr53c400=iobase,irq

If the card doesn’t use interrupts, then an IRQ value of 255 (0xff)
will disable interrupts. An IRQ value of 254 means to autoprobe. More
details can be found in the file
/usr/src/linux/drivers/scsi/README.g_NCR5380.

NCR53C8xx configuration
ncr53c8xx=S

where S is a comma-separated string of items keyword:value. Recog-
nized 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 /usr/src/linux/drivers/scsi/ncr53c8xx.c.

NCR53c406a configuration
ncr53c406a=iobase[,irq[,fastpio]]

Specify irq = 0 for non-interrupt driven mode. Set fastpio = 1 for
fast pio mode, 0 for slow mode.

Pro Audio Spectrum configuration
The PAS16 uses a NC5380 SCSI chip, and newer models support jumperless
configuration. The boot arg is of the form:

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 follow-
ing options:

t128=mem_base,irq

The valid values for mem_base are as follows: 0xcc000, 0xc8000,
0xdc000, 0xd8000.

UltraStor 14F/34F configuration
The default list of i/o ports to be probed can be changed by

eata=iobase,iobase,....

WD7000 configuration
wd7000=irq,dma,iobase

Commodore Amiga A2091/590 SCSI controller configuration
wd33c93=S

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 /usr/src/linux/drivers/scsi/wd33c93.c.

HARD DISKS
IDE Disk/CD-ROM Driver Parameters
The IDE driver accepts a number of parameters, which range from disk
geometry 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 operations to enable the sec-
ond interface and to enable faster transfer modes.

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

hdb=noprobe hdb=1166,7,17

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

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

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

Standard ST-506 Disk Driver Options (‘hd=’)
The standard disk driver can accept geometry arguments for the disks
similar to the IDE driver. Note however that it only expects three
values (C/H/S) -- any more or any less and it will silently ignore
you. Also, it only accepts ‘hd=’ as an argument, 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 geom-
etry 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,
overriding autodetection. For the types to use, consult the
drivers/block/xd.c source file of the kernel you are using. The type
is an index in the list xd_sigs and in the course of time types have
been added to or deleted from the middle of the list, changing all
type numbers. Today (Linux 2.5.0) the types are 0=generic; 1=DTC
5150cx; 2,3=DTC 5150x; 4,5=Western Digital; 6,7,8=Seagate; 9=Omti;
10=XEBEC, and where here several types are given with the same desig-
nation, they are equivalent.

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

xd=2,5,0x320,3

Syquest’s EZ* removable disks
ez=iobase[,irq[,rep[,nybble]]]

IBM MCA BUS DEVICES
See also /usr/src/linux/Documentation/mca.txt.

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

ed=cyls,heads,sectors.

For a ThinkPad-720, add the option

tp720=1.

IBM Microchannel SCSI Subsystem configuration
ibmmcascsi=N

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

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.

Parallel port CD-ROM drives
Syntax:

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

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

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

cdu31a=iobase,[irq[,is_pas_card]]

Specifying an IRQ value of zero tells the driver that hardware inter-
rupts 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 Spec-
trum card, and otherwise it should not be specified at all.

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

sonycd535=iobase[,irq]

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

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

gscd=iobase

The ISP16 CD-ROM Interface
Syntax:

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

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

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

mcd=iobase,[irq[,wait_value]]

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

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

mcdx=iobase[,irq]

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

optcd=iobase

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

cm206=[iobase][,irq]

The driver assumes numbers between 3 and 11 are IRQ values, and num-
bers 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: ‘Sound-
Blaster’, ‘LaserMate’, or ‘SPEA’. The I/O base is that of the CD-ROM
interface, and not that of the sound portion of the card.

ETHERNET DEVICES
Different drivers make use of different parameters, but they all at
least share having an IRQ, an I/O port base value, and a name. In its
most generic form, it looks something like this:

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

The first non-numeric argument is taken as the name. The param_n val-
ues (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 accom-
plished with a simple:

ether=0,0,eth1

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

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

THE FLOPPY DISK DRIVER
There are many floppy driver options, and they are all listed in
README.fd in linux/drivers/block. This information 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 cer-
tain non-standard hardware (ASUS PCI motherboards) mess up the key-
board 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)

floppy=daring
Tells the floppy driver that you have a well behaved floppy con-
troller. This allows more efficient and smoother operation, but may
fail on certain controllers. This may speed up certain operations.

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

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

floppy=two_fdc or floppy=address,two_fdc
Tells the floppy driver that you have two floppy controllers. The sec-
ond 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.)

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...[,device10]]]

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

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

aaa - I/O address in hex.

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

d - DMA channel.

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

ISDN DRIVERS
The ICN ISDN driver
Syntax:

icn=iobase,membase,icn_id1,icn_id2

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

The PCBIT ISDN driver
Syntax:

pcbit=membase1,irq1[,membase2,irq2]

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

The Teles ISDN driver
Syntax:

teles=iobase,irq,membase,protocol,teles_id

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

SERIAL PORT DRIVERS
The RISCom/8 Multiport Serial Driver (‘riscom8=’)
Syntax:

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

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

The DigiBoard Driver (‘digi=’)
If this option is used, it should have precisely six parameters. Syn-
tax:

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

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

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

More details can be found in /usr/src/linux/Documentation/digi-
board.txt.

The Baycom Serial/Parallel Radio Modem
Syntax:

baycom=iobase,irq,modem

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 sup-
ported modem types. For more details, see
/usr/src/linux/drivers/net/README.baycom.

Soundcard radio modem driver
Syntax:

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

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

THE LINE PRINTER DRIVER
‘lp=’
Syntax:

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

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

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

WDT500/501 driver
Syntax:

wdt=io,irq

MOUSE DRIVERS
‘bmouse=irq’
The busmouse driver only accepts one parameter, that being the hard-
ware IRQ value to be used.

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

ATARI mouse setup
atamouse=threshold[,y-threshold]

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

VIDEO HARDWARE
‘no-scroll’
This option tells the console driver not to use hardware scroll (where
a scroll is effected by moving the screen origin in video memory,
instead of moving the data). It is required by certain Braille
machines.

AUTHORS
Linus Torvalds (and many others)

SEE ALSO
klogd(8), lilo.conf(5), lilo(8), mount(8), rdev(8)

Large parts of this man page have been derived from the Boot Parameter
HOWTO (version 1.0.1) written by Paul Gortmaker. More information may
be found in this (or a more recent) HOWTO. An uptodate source of
information is /usr/src/linux/Documentation/kernel-parameters.txt.

Linux 2.1.21 1995-01-14 BOOTPARAM(7)