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BOOTPARAM(7) Linux Programmer’s Manual BOOTPARAM(7)
NAME
bootparam - Introduction to boot time parameters of the Linux kernel
DESCRIPTION
The Linux kernel accepts certain ‘command line options’ or ‘boot time parameters’
at the moment it is started. In general this is used to supply the kernel with
information about hardware parameters that the kernel would not be able to deter-
mine 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 parame-
ters one can also modify the kernel image itself, using rdev, see rdev(8) for fur-
ther 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 program that has
the capability to launch a Linux kernel from the DOS prompt (with boot-args) assum-
ing 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 ‘Sound-
Blaster Compatible’ sound cards that require the DOS driver to twiddle a few mysti-
cal registers to put the card into a SB compatible mode. Booting DOS with the sup-
plied 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 arguments) 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. (How-
ever, you can re-use the same keyword with up to an additional 10 parameters in
unusually complicated situations, assuming the setup function supports it.)
Most of the sorting goes on in linux/init/main.c. First, the kernel checks to see
if the argument is any of the special arguments ‘root=’, ‘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 func-
tion 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 inter-
preted 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
â€â€˜init=...â€â€™
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.
â€â€˜nfsaddrs=...â€â€™
This sets the nfs boot address to the given string. This boot address is used in
case of a net boot.
â€â€˜nfsroot=...â€â€™
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.
â€â€˜no387â€â€™
(Only when CONFIG_BUGi386 is defined.) Some i387 coprocessor chips have bugs that
show up when used in 32 bit protected mode. For example, some of the early ULSI-387
chips would cause solid lockups while performing floating point 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!
â€â€˜no-hltâ€â€™
(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.
â€â€˜root=...â€â€™
This argument tells the kernel what device is to be used as the root filesystem
while booting. The default of this setting is determined at compile time, and usu-
ally is the value of the root device of the system that the kernel was built on. To
override this value, and select the second floppy drive as the root device, one
would use ‘root=/dev/fd1’. (The root device can also be set using rdev(8).)
The root device can be specified symbolically or numerically. A symbolic specifi-
cation has the form /dev/XXYN, where XX designates the device type (‘hd’ for ST-506
compatible hard disk, with Y in ‘a’-‘d’; ‘sd’ for SCSI compatible disk, with Y in
‘a’-‘e’; ‘ad’ for Atari ACSI disk, with Y in ‘a’-‘e’, ‘ez’ for a Syquest EZ135 par-
allel port removable drive, with Y=‘a’, ‘xd’ for XT compatible disk, with Y either
‘a’ or ‘b’; ‘fd’ for floppy disk, with Y the floppy drive number - fd0 would be the
DOS ‘A:’ drive, and fd1 would be ‘B:’), Y the driver letter or number, and N the
number (in decimal) of the partition on this device (absent in the case of flop-
pies). Recent kernels allow many other types, mostly for CD-ROMs: nfs, ram, scd,
mcd, cdu535, aztcd, cm206cd, gscd, sbpcd, sonycd, bpcd. (The type nfs specifies a
net boot; ram refers to a ram disk.)
Note that this has nothing to do with the designation of these devices on your 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.)
â€â€˜roâ€â€™ and â€â€˜rwâ€â€™
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).
â€â€˜reserve=...â€â€™
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 argu-
ment 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.
â€â€˜mem=...â€â€™
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 indi-
cates 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.
â€â€˜panic=Nâ€â€™
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".
â€â€˜reboot=[warm|cold][,[bios|hard]]â€â€™
(Only when CONFIG_BUGi386 is defined.) Since 2.0.22 a reboot is by default a cold
reboot. One asks for the old default with ‘reboot=warm’. (A cold reboot may be
required to reset certain hardware, but might destroy not yet written data in a
disk cache. A warm reboot may be faster.) By default a reboot is hard, by asking
the keyboard controller to pulse the reset line low, but there is at least one type
of motherboard where that doesn’t work. The option ‘reboot=bios’ will instead jump
through the BIOS.
â€â€˜nosmpâ€â€™ and â€â€˜maxcpus=Nâ€â€™
(Only when __SMP__ is defined.) A command-line option of ‘nosmp’ or ‘maxcpus=0’
will disable SMP activation entirely; an option ‘maxcpus=N’ limits the maximum num-
ber of CPUs activated in SMP mode to N.
BOOT ARGUMENTS FOR USE BY KERNEL DEVELOPERS
â€â€˜debugâ€â€™
Kernel messages are handed off to the kernel log daemon klogd so that they may be
logged to disk. Messages with a priority above console_loglevel are also printed on
the console. (For these levels, see <linux/kernel.h>.) By default this 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).
â€â€˜profile=Nâ€â€™
It is possible to enable a kernel profiling function, if one wishes to find out
where the kernel is spending its CPU cycles. Profiling is enabled by setting the
variable prof_shift to a nonzero value. This is done either by specifying CON-
FIG_PROFILE at compile time, or by giving the ‘profile=’ option. Now the value
that prof_shift gets will be N, when given, or CONFIG_PROFILE_SHIFT, when that is
given, or 2, the default. The significance of this variable is that it gives the
granularity of the profiling: each clock tick, if the system was executing kernel
code, a counter is incremented:
profile[address >> prof_shift]++;
The raw profiling information can be read from /proc/profile. Probably you’ll want
to use a tool such as readprofile.c to digest it. Writing to /proc/profile will
clear the counters.
â€â€˜swap=N1,N2,N3,N4,N5,N6,N7,N8â€â€™
Set the eight parameters max_page_age, page_advance, page_decline, page_ini-
tial_age, age_cluster_fract, age_cluster_min, pageout_weight, bufferout_weight that
control the kernel swap algorithm. For kernel tuners only.
â€â€˜buff=N1,N2,N3,N4,N5,N6â€â€™
Set the six parameters max_buff_age, buff_advance, buff_decline, buff_initial_age,
bufferout_weight, buffermem_grace that control kernel buffer memory management. For
kernel tuners only.
BOOT ARGUMENTS FOR RAMDISK USE
(Only if the kernel was compiled with CONFIG_BLK_DEV_RAM.) In general it is a bad
idea to use a ramdisk under Linux - the system will use available memory more
efficiently itself. But while booting (or while constructing boot floppies) it is
often useful to load the floppy contents into a ramdisk. One might also have a sys-
tem 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.
â€â€˜load_ramdisk=Nâ€â€™
If N=1, do load a ramdisk. If N=0, do not load a ramdisk. (This is the default.)
â€â€˜prompt_ramdisk=Nâ€â€™
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.)
â€â€˜ramdisk_size=Nâ€â€™ or (obsolete) â€â€˜ramdisk=Nâ€â€™
Set the maximal size of the ramdisk(s) to N kB. The default is 4096 (4 MB).
â€â€˜ramdisk_start=Nâ€â€™
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.
â€â€˜noinitrdâ€â€™
(Only if the kernel was compiled with CONFIG_BLK_DEV_RAM and CONFIG_BLK_DEV_INI-
TRD.) These days it is possible to compile the kernel to use initrd. When this
feature is enabled, the boot process will load the kernel and an initial ramdisk;
then the kernel converts initrd into a "normal" ramdisk, which is mounted read-
write as root device; then /linuxrc is executed; 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/Documenta-
tion/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 usually be 5, 7, 9, 10, 11, 12,
and 15. The other values are usually used for common peripherals like IDE hard
disks, floppies, serial ports, etc.
scsi-id -- the ID that the host adapter uses to identify itself on the SCSI bus.
Only some host adapters allow you to change this value, as most have it permanently
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.
â€â€˜max_scsi_luns=...â€â€™
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 ‘Logical Unit Number’ (LUN) of that particular
device. But most devices, such as hard disks, tape drives and such are only one
device, and will be assigned to LUN zero.
Some poorly designed SCSI devices cannot handle being probed for LUNs not equal to
zero. Therefore, if the compile time flag CONFIG_SCSI_MULTI_LUN is not set, newer
kernels will by default only probe LUN zero.
To specify the number of probed LUNs at boot, one enters ‘max_scsi_luns=n’ as a
boot arg, where n is a number between one and eight. To avoid problems as described
above, one would use n=1 to avoid upsetting such broken devices.
SCSI tape configuration
Some boot time configuration of the SCSI tape driver can be achieved by using the
following:
st=buf_size[,write_threshold[,max_bufs]]
The first two numbers are specified in units of kB. The default buf_size is 32kB,
and the maximum size that can be specified is a ridiculous 16384kB. The
write_threshold is the value at which the buffer is committed to tape, with a
default value of 30kB. The maximum number of buffers varies with the number of
drives detected, and has a default of two. An example usage would be:
st=32,30,2
Full details can be found in the 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 exam-
ple usage is as follows:
aha152x=0x340,11,7,1
Note that the parameters must be specified in order, meaning that if you want to
specify a parity setting, then you will have to specify an iobase, irq, scsi-id and
reconnect value as well.
Adaptec aha154x configuration
The aha1542 series cards have an i82077 floppy controller onboard, while the
aha1540 series cards do not. These are busmastering cards, and have parameters to
set the ‘‘fairness’’ that is used to share the bus with other devices. The boot 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 domi-
nates the ISA bus. The defaults are 11us on, and 4us off, so that other cards (such
as an ISA LANCE Ethernet card) have a chance to get access to the ISA bus.
The dmaspeed value refers to the rate (in MB/s) at which the DMA (Direct Memory
Access) transfers proceed. The default is 5MB/s. Newer revision cards allow you to
select this value as part of the soft-configuration, older cards use jumpers. You
can use values up to 10MB/s assuming that your motherboard is capable of 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 (â€â€˜advansys=â€â€™)
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 addi-
tion, if the driver has been compiled with debugging enabled, the level of debug-
ging output can be set by adding an 0xdeb[0-f] parameter. The 0-f allows setting
the level of the debugging messages to any of 16 levels of verbosity.
AM53C974
AM53C974=host-scsi-id,target-scsi-id,max-rate,max-offset
BusLogic SCSI Hosts configuration (â€â€˜BusLogic=â€â€™)
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 abbreviated extract.
The parameters N1-N5 are integers. The parameters S1,... are strings. N1 is the
I/O Address at which the Host Adapter is located. N2 is the Tagged Queue Depth to
use for Target Devices that support Tagged Queuing. N3 is the Bus Settle Time in
seconds. This is the amount of time to wait between a Host Adapter Hard Reset
which initiates a SCSI Bus Reset and issuing any SCSI Commands. N4 is the Local
Options (for one Host Adapter). N5 is the Global Options (for all Host Adapters).
The string options are used to provide control over Tagged Queuing (TQ:Default,
TQ:Enable, TQ:Disable, TQ:<Per-Target-Spec>), over Error Recovery (ER:Default,
ER:HardReset, ER:BusDeviceReset, ER:None, ER:<Per-Target-Spec>), and over Host
Adapter Probing (NoProbe, NoProbeISA, NoSortPCI).
EATA/DMA configuration
The default list of i/o ports to be probed can be changed by
eata=iobase,iobase,....
Future Domain TMC-16x0 configuration
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]. 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
/usr/src/linux/drivers/scsi/in2000.c.
NCR5380 and NCR53C400 configuration
The boot arg is of the form
ncr5380=iobase,irq,dma
or
ncr53c400=iobase,irq
If the card doesn’t use interrupts, then an IRQ value of 255 (0xff) will disable
interrupts. An IRQ value of 254 means to autoprobe. More details can be found in
the file /usr/src/linux/drivers/scsi/README.g_NCR5380.
NCR53C8xx configuration
ncr53c8xx=S
where S is a comma-separated string of items keyword:value. Recognized keywords
are: mpar (master_parity), spar (scsi_parity), disc (disconnection), specf (spe-
cial_features), ultra (ultra_scsi), fsn (force_sync_nego), tags (default_tags),
sync (default_sync), verb (verbose), debug (debug), burst (burst_max). For the
function of the assigned values, see /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 configura-
tion. The boot arg is of the form:
pas16=iobase,irq
The only difference is that you can specify an IRQ value of 255, which will tell
the driver to work without using interrupts, albeit at a performance loss. The
iobase is usually 0x388.
Seagate ST-0x configuration
If your card is not detected at boot time, you will then have to use a boot arg of
the form:
st0x=mem_base,irq
The mem_base value is the value of the memory mapped I/O region that the card uses.
This will usually be one of the following values: 0xc8000, 0xca000, 0xcc000,
0xce000, 0xdc000, 0xde000.
Trantor T128 configuration
These cards are also based on the NCR5380 chip, and accept the following options:
t128=mem_base,irq
The valid values for mem_base are as follows: 0xcc000, 0xc8000, 0xdc000, 0xd8000.
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:bit-
mask, 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 spec-
ifications, to support for broken controller chips. Drive specific options are
specified by using ‘hdX=’ with X in ‘a’-‘h’.
Non-drive specific options are specified with the prefix ‘hd=’. Note that using a
drive specific prefix for a non-drive specific option will still work, and the
option will just be applied as expected.
Also note that ‘hd=’ can be used to refer to the next unspecified drive in the (a,
..., h) sequence. For the following discussions, the ‘hd=’ option will be cited
for brevity. See the file README.ide in linux/drivers/block for more details.
The â€â€˜hd=cyls,heads,sects[,wpcom[,irq]]â€â€™ 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 â€â€˜hd=serializeâ€â€™ 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 â€â€˜hd=dtc2278â€â€™ option
This option tells the driver that you have a DTC-2278D IDE interface. The driver
then tries to do DTC specific operations to enable the second interface and to
enable faster transfer modes.
The â€â€˜hd=noprobeâ€â€™ 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 â€â€˜hd=nowerrâ€â€™ option
Some drives apparently have the WRERR_STAT bit stuck on permanently. This enables
a work-around for these broken devices.
The â€â€˜hd=cdromâ€â€™ option
This tells the IDE driver that there is an ATAPI compatible CD-ROM attached in
place of a normal IDE hard disk. In most cases the CD-ROM is identified automati-
cally, but if it isn’t then this may help.
Standard ST-506 Disk Driver Options (â€â€˜hd=â€â€™)
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 argu-
ment, i.e. ‘hda=’ and so on are not valid here. The format is as follows:
hd=cyls,heads,sects
If there are two disks installed, the above is repeated with the geometry parame-
ters of the second disk.
XT Disk Driver Options (â€â€˜xd=â€â€™)
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 designation, they are equivalent.
The xd_setup() function does no checking on the values, and assumes that you
entered all four values. Don’t disappoint it. Here is an example usage for a
WD1002 controller with the BIOS disabled/removed, using the ‘default’ XT controller
parameters:
xd=2,5,0x320,3
Syquestâ€â€™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 auto-
matically), ‘slv’ is 1 if it should be a slave, and ‘dly’ is a small integer for
slowing down port accesses. The ‘nice’ parameter controls the driver’s use of idle
CPU time, at the expense of some speed.
The CDU-31A and CDU-33A Sony Interface
This CD-ROM interface is found on some of the Pro Audio Spectrum sound cards, and
other Sony supplied interface cards. The syntax is as follows:
cdu31a=iobase,[irq[,is_pas_card]]
Specifying an IRQ value of zero tells the driver that hardware interrupts aren’t
supported (as on some PAS cards). If your card supports interrupts, you should use
them as it cuts down on the CPU usage of the driver.
The is_pas_card should be entered as ‘PAS’ if using a Pro Audio Spectrum card, and
otherwise it should not be specified at all.
The CDU-535 Sony Interface
The syntax for this CD-ROM interface is:
sonycd535=iobase[,irq]
A zero can be used for the I/O base as a ‘placeholder’ if one wishes to specify an
IRQ value.
The GoldStar Interface
The syntax for this CD-ROM interface is:
gscd=iobase
The ISP16 CD-ROM Interface
Syntax:
isp16=[iobase[,irq[,dma[,type]]]]
(three integers and a string). If the type is given as ‘noisp16’, the interface
will not be configured. Other recognized types are: ‘Sanyo", ‘Sony’, ‘Panasonic’
and ‘Mitsumi’.
The Mitsumi Standard Interface
The syntax for this CD-ROM interface is:
mcd=iobase,[irq[,wait_value]]
The wait_value is used as an internal timeout value for people who are having prob-
lems with their drive, and may or may not be implemented depending on a compile
time #define. The Mitsumi FX400 is an IDE/ATAPI CD-ROM player and does not use the
mcd driver.
The Mitsumi XA/MultiSession Interface
This is for the same hardware as above, but the driver has extended features. Syn-
tax:
mcdx=iobase[,irq]
The Optics Storage Interface
The syntax for this type of card is:
optcd=iobase
The Phillips CM206 Interface
The syntax for this type of card is:
cm206=[iobase][,irq]
The driver assumes numbers between 3 and 11 are IRQ values, and numbers between
0x300 and 0x370 are I/O ports, so you can specify one, or both numbers, in any
order. It also accepts ‘cm206=auto’ to enable autoprobing.
The Sanyo Interface
The syntax for this type of card is:
sjcd=iobase[,irq[,dma_channel]]
The SoundBlaster Pro Interface
The syntax for this type of card is:
sbpcd=iobase,type
where type is one of the following (case sensitive) strings: ‘SoundBlaster’,
‘LaserMate’, or ‘SPEA’. The I/O base is that of the CD-ROM interface, and not that
of the sound portion of the card.
ETHERNET DEVICES
Different drivers make use of different parameters, but they all at least share
having an IRQ, an I/O port base value, and a name. In its most generic form, it
looks something like this:
ether=irq,iobase[,param_1[,...param_8]],name
The first non-numeric argument is taken as the name. The param_n values (if appli-
cable) usually have different meanings for each different card/driver. Typical
param_n values are used to specify things like shared memory address, interface
selection, DMA channel and the like.
The most common use of this parameter is to force probing for a second ethercard,
as the default is to only probe for one. This can be accomplished with a simple:
ether=0,0,eth1
Note that the values of zero for the IRQ and I/O base in the above example tell the
driver(s) to autoprobe.
The Ethernet-HowTo has extensive documentation on using multiple cards and on the
card/driver specific 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 certain non-standard hardware
(ASUS PCI motherboards) mess up the keyboard when accessing units 2 or 3. This
option is somewhat obsoleted by the cmos option.
floppy=all_drives
Sets the bitmask of allowed drives to all drives. Use this if you have more than
two drives connected to a floppy controller.
floppy=asus_pci
Sets the bitmask to allow only units 0 and 1. (The default)
floppy=daring
Tells the floppy driver that you have a well behaved floppy controller. This
allows more efficient and smoother operation, but may fail on certain controllers.
This may speed up certain operations.
floppy=0,daring
Tells the floppy driver that your floppy controller should be used with caution.
floppy=one_fdc
Tells the floppy driver that you have only floppy controller (default)
floppy=two_fdc or floppy=address,two_fdc
Tells the floppy driver that you have two floppy controllers. The second floppy
controller is assumed to be at address. If address is not given, 0x370 is assumed.
floppy=thinkpad
Tells the floppy driver that you have a Thinkpad. Thinkpads use an inverted conven-
tion 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 inter-
rupt setting of the N’th card. The default is IRQ 5 and membase 0xD0000.
The Teles ISDN driver
Syntax:
teles=iobase,irq,membase,protocol,teles_id
where iobase is the i/o port address of the card, membase is the shared memory base
address of the card, irq is the interrupt channel the card uses, and teles_id is
the unique ASCII string identifier.
SERIAL PORT DRIVERS
The RISCom/8 Multiport Serial Driver (â€â€˜riscom8=â€â€™)
Syntax:
riscom=iobase1[,iobase2[,iobase3[,iobase4]]]
More details can be found in /usr/src/linux/Documentation/riscom8.txt.
The DigiBoard Driver (â€â€˜digi=â€â€™)
If this option is used, it should have precisely six parameters. Syntax:
digi=status,type,altpin,numports,iobase,membase
The parameters maybe given as integers, or as strings. If strings are used, then
iobase and membase should be given in hexadecimal. The integer arguments (fewer
may be given) are in order: status (Enable(1) or Disable(0) this card), type
(PC/Xi(0), PC/Xe(1), PC/Xeve(2), PC/Xem(3)), altpin (Enable(1) or Disable(0) alter-
nate pin arrangement), numports (number of ports on this card), iobase (I/O Port
where card is configured (in HEX)), membase (base of memory window (in HEX)).
Thus, the following two boot prompt arguments are equivalent:
digi=E,PC/Xi,D,16,200,D0000
digi=1,0,0,16,0x200,851968
More details can be found in /usr/src/linux/Documentation/digiboard.txt.
The Baycom Serial/Parallel Radio Modem
Syntax:
baycom=iobase,irq,modem
There are precisely 3 parameters; for several cards, give several ‘baycom=’ com-
mands. The modem parameter is a string that can take one of the values ser12,
ser12*, par96, par96*. Here the * denotes that software DCD is to be used, and
ser12/par96 chooses between the supported modem types. For more details, see
/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
â€â€˜lp=â€â€™
Syntax:
lp=0
lp=auto
lp=reset
lp=port[,port...]
You can tell the printer driver what ports to use and what ports not to use. The
latter comes in handy if you don’t want the printer driver to claim all available
parallel ports, so that other drivers (e.g. PLIP, PPA) can use them instead.
The format of the argument is multiple port names. For example, lp=none,parport0
would use the first parallel port for lp1, and disable lp0. To disable the printer
driver entirely, one can use lp=0.
WDT500/501 driver
Syntax:
wdt=io,irq
MOUSE DRIVERS
â€â€˜bmouse=irqâ€â€™
The busmouse driver only accepts one parameter, that being the hardware IRQ value
to be used.
â€â€˜msmouse=irqâ€â€™
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-thresh-
old. Otherwise, the first argument is the x-threshold, and the second the y-
threshold. These values must lie between 1 and 20 (inclusive); the default
is 2.
VIDEO HARDWARE
â€â€˜no-scrollâ€â€™
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 (ver-
sion 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/Documenta-
tion/kernel-parameters.txt.
Linux 2.1.21 1995-01-14 BOOTPARAM(7)
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