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The Linux BootPrompt-HowTo
by Paul Gortmaker.
v1.4, Mar 21, 2003
This is the BootPrompt-Howto, which is a compilation of all the possi­
ble boot time arguments that can be passed to the Linux kernel at boot
time. A discussion of how the kernel sorts boot time arguments,
along with an overview of some of the popular software used to boot
Linux kernels is also included.
______________________________________________________________________
Table of Contents
1. Introduction
1.1 Intended Audience and Applicability
1.2 Related Documentation
1.3 New Versions of this Document
2. Overview of Boot Prompt Arguments
2.1 LILO (LInux LOader)
2.2 LoadLin
2.3 The ``rdev'' utility
2.4 How the Kernel Sorts the Arguments
2.5 Setting Environment Variables.
2.6 Passing Arguments to the `init' program
3. General Non-Device Specific Boot Args
3.1 Root Filesystem options
3.1.1 The `root=' Argument
3.1.2 The `rootflags=' Argument
3.1.3 The `rootfstype=' Argument
3.1.4 The `ro' Argument
3.1.5 The `rw' Argument
3.1.6 The `nfsroot=' Argument
3.1.7 The `ip=' or `nfsaddrs=' Argument
3.2 Options Relating to RAM Disk Management
3.2.1 The `ramdisk_start=' Argument
3.2.2 The `load_ramdisk=' Argument
3.2.3 The `prompt_ramdisk=' Argument
3.2.4 The `ramdisk_size=' Argument
3.2.5 The `ramdisk_blocksize=' Argument
3.2.6 The `ramdisk=' Argument (obsolete)
3.2.7 The `noinitrd' (initial RAM disk) Argument
3.3 Boot Arguments Related to Memory Handling
3.3.1 The `cachesize=' Argument
3.3.2 The `mem=' Argument
3.3.3 The `memfrac=' Argument
3.3.4 The `swap=' Argument
3.3.5 The `buff=' Argument
3.4 Other Misc. Kernel Boot Arguments
3.4.1 The `acpi=' Argument
3.4.2 The `console=' Argument
3.4.3 The `debug' Argument
3.4.4 The `decnet=' Argument
3.4.5 The `devfs=' Argument
3.4.6 The `gpt' Argument
3.4.7 The `idle=' Argument
3.4.8 The `init=' Argument
3.4.9 The `isapnp=' Argument
3.4.10 The `isapnp_reserve_dma=' Argument
3.4.11 The `isapnp_reserve_io=' Argument
3.4.12 The `isapnp_reserve_irq=' Argument
3.4.13 The `isapnp_reserve_mem=' Argument
3.4.14 The `kbd-reset' Argument
3.4.15 The `lockd.udpport=' and `lockd.tcpport' Argument
3.4.16 The `maxcpus=' Argument
3.4.17 The `mca-pentium' Argument
3.4.18 The `md=' Argument
3.4.19 The `nmi_watchdog=' Argument
3.4.20 The `no387' Argument
3.4.21 The `no-hlt' Argument
3.4.22 The `no-scroll' Argument
3.4.23 The `noapic' Argument
3.4.24 The `noht' Argument
3.4.25 The `noisapnp' Argument
3.4.26 The `nomce' Argument
3.4.27 The `nosmp' Argument
3.4.28 The `noresume' Argument
3.4.29 The `notsc' Argument
3.4.30 The `nofxsr" Argument
3.4.31 The `panic=' Argument
3.4.32 The `pirq=' Argument
3.4.33 The `profile=' Argument
3.4.34 The `quiet' Argument
3.4.35 The `raid=' Argument
3.4.36 The `reboot=' Argument
3.4.37 The `reserve=' Argument
3.4.38 The `resume=' Argument
3.4.39 The `vga=' Argument
4. Boot Arguments to Control PCI Bus Behaviour (`pci=')
4.1 The `pci=assign-busses' Argument
4.2 The `pci=bios' and `pci=nobios' Arguments
4.3 The `pci=conf1' and `pci=conf2' Arguments
4.4 The `pci=irqmask=' Argument
4.5 The `pci=lastbus=' Argument
4.6 The `pci=noacpi' Argument
4.7 The `pci=nopeer' Argument
4.8 The `pci=nosort' Argument
4.9 The `pci=off' Argument
4.10 The `pci=usepirqmask' Argument
4.11 The `pci=rom' Argument
5. Boot Arguments for Video Frame Buffer Drivers
5.1 The `video=map:...' Argument
5.2 The `video=scrollback:...' Argument
5.3 The `video=vc:...' Argument
6. Boot Arguments for SCSI Peripherals.
6.1 Arguments for Upper and Mid-level Drivers
6.1.1 Maximum Probed LUNs (`max_scsi_luns=')
6.1.2 SCSI Logging (`scsi_logging=')
6.1.3 Parameters for the SCSI Tape Driver (`st=')
6.2 Arguments for SCSI Host Adapter Drivers
7. Hard Disks
7.1 IDE Disk/CD-ROM Driver Parameters
7.2 Old MFM/RLL/Standard ST-506 Disk Driver Options (`hd=')
7.3 XT Disk Driver Options (`xd=', `xd_geo=')
8. The Sound Drivers
8.1 Individual Sound Device Driver Arguments
8.1.1 ALSA ISA drivers
8.1.2 OSS drivers
8.1.3 ALSA PCI Drivers
9. CD-ROMs (Non-SCSI/ATAPI/IDE)
9.1 Old CD-ROM Driver Arguments
10. Serial and ISDN Drivers
10.1 The ISDN drivers
10.2 The Serial drivers
11. Other Hardware Devices
11.1 Ethernet Devices (`ether=', `netdev=')
11.2 The Floppy Disk Driver (`floppy=')
11.3 The Bus Mouse Driver (`bmouse=')
11.4 The MS Bus Mouse Driver (`msmouse=')
11.5 The Printer Driver (`lp=')
11.6 The Parallel port IP driver (`plip=')
12. Copying, Translations, Closing, etc.
12.1 Copyright and Disclaimer
12.2 Closing
______________________________________________________________________
1. Introduction
The kernel has the capability to accept information at boot in the
form of a `command line', similar to an argument list you would give
to a program. 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.
It is the job of the boot loader (e.g. LILO, loadlin or Grub) to take
this information from the user and put it in a previously agreed upon
place where the kernel can find it once it starts.
This present revision covers kernels up to and including v2.4.20. and
v2.5.63
The BootPrompt-Howto is by:
Paul Gortmaker, p_gortmaker @ yahoo.com
This document is Copyright (c) 1995-2003 by Paul Gortmaker. Please
see the Disclaimer and Copying information at the end of this document
(``copyright'') for information about redistribution of this document
and the usual `we are not responsible for what you manage to break...'
type legal stuff.
1.1. Intended Audience and Applicability
Most Linux users should never have to even look at this document.
Linux does an exceptionally good job at detecting most hardware and
picking reasonable default settings for most parameters. The
information in this document is aimed at users who might want to
change some of the default settings to optimize the kernel to their
particular machine, or to a user who has `rolled their own' kernel to
support a not so common piece of hardware for which the automatic
defaults are not optimal.
For the sake of this document it is best to break the boot arguments
into two general categories; (a)ones handled by the kernel and
(b)those being handled by a device driver. Examples would be init=
which tells the kernel what the first program to run should be, versus
aha154x= which tells a device driver for a SCSI card what hardware
resources it should use are. This document concentrates on giving
detailed information on those in (a) for reasons outlined below.
IMPORTANT NOTE: Driver related boot prompt arguments only apply to
hardware drivers that are compiled directly into the kernel. They have
no effect on drivers that are loaded as modules. Most Linux
distributions come with a basic `bare-bones' kernel, and the drivers
are small modules that are loaded after the kernel has initialized.
If you are unsure if you are using modules then try lsmod, look at man
depmod and man modprobe along with the contents of your
/etc/modules.conf.
In light of this, device driver boot prompt arguments are only really
used by a few people who are building their own kernels, and thus have
the kernel source at hand. These people are usually going to check
the source for the options and syntax required by that driver to get
the most up to date info.
For example, if you were looking for what arguments could be passed to
the AHA1542 SCSI driver, then you would go to the linux/drivers/scsi
directory, and look in the file aha1542.c for __setup(... , ...). The
first thing in brackets is the argument you provide at boot, and the
second thing is the name of the function that processes your argument.
Usually near the top of this function or at the top of the source file
you will find a description of the boot time arguments that the driver
accepts.
1.2. Related Documentation
For a while now, the kernel source has come with the file
linux/Documentation/kernel-parameters.txt. This file contains a brief
listing of all the boot time arguments that you can provide, along
with quick pointers to where in the source you can find where the
arguments are parsed. The idea is that this file gives developers a
quick and easy place to add in a brief description of any new
arguments that they add while working on the source. As such, it will
probably always be more up to date than this document. Actually, I'm
considering discontinuing this document in light of the existence of
kernel-parameters.txt. (Opinions?)
The linux directory is usually found in /usr/src/ for most
distributions. All references in this document to files that come
with the kernel will have their pathname abbreviated to start with
linux - you will have to add the /usr/src/ or whatever is appropriate
for your system. Some distributions may not install the full kernel
source by default, and only put in the linux/include directory. If
you can't find the file in question, then install the kernel source
and/or make use of the find and locate commands. If you can't find
the kernel source package in your distribution then the kernel source
is available at:
Kernel Source Home <http://www.kernel.org>
The next best thing to reading the kernel C source itself, will be any
of the other documentation files that are distributed with the kernel
itself. There are now quite a few of these, and most of them can be
found in the directory linux/Documentation and subdirectories from
there. Sometimes there will be README.foo files that can be found in
the related driver directory (e.g. linux/drivers/???/, where examples
of ??? could be scsi, char, or net). The general trend is to move
these files into the Documentation directory, so if a file mentioned
in this document is no longer there, chances are it has been moved.
If you have figured out what boot-args you intend to use, and now want
to know how to get that information to the kernel, then look at the
documentation that comes with the software that you use to boot the
kernel (e.g. LILO or loadlin). A brief overview is given below, but it
is no substitute for the documentation that comes with the booting
software.
1.3. New Versions of this Document
New versions of this document can be retrieved via anonymous FTP from
most Linux FTP sites in the directory /pub/Linux/docs/HOWTO/. Updates
will be made as new information and/or drivers becomes available. If
this copy that you are presently reading is more than six months old,
then you should probably check to see if a newer copy exists. I would
recommend viewing this via a WWW browser or in the Postscript/dvi
format. Both of these contain cross-references that are lost in a
simple plain text version.
If you want to get the official copy, here is URL.
BootPrompt-HOWTO <http://metalab.unc.edu/mdw/HOWTO/BootPrompt-
HOWTO.html>
2. Overview of Boot Prompt Arguments
This section gives some examples of software that can be used to pass
kernel boot-time arguments to the kernel itself. It also gives you an
idea of how the arguments are processed, what limitations there are on
the boot args, and how they filter down to each appropriate device
that they are intended for.
It is important to note that spaces should not be used in a boot
argument, but only between separate arguments. A list of values that
are for a single argument are to be separated with a comma between the
values, and again without any spaces. See the following examples
below.
______________________________________________________________________
ether=9,0x300,0xd0000,0xd4000,eth0 root=/dev/hda1 *RIGHT*
ether = 9, 0x300, 0xd0000, 0xd4000, eth0 root = /dev/hda1 *WRONG*
______________________________________________________________________
Once the Linux kernel is up and running, one can view the command line
arguments that were in place at boot by simply typing cat
/proc/cmdline at a shell prompt.
2.1. LILO (LInux LOader)
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. Most
distributions ship with LILO as the default boot-loader. LILO can boot
DOS, OS/2, Linux, FreeBSD, etc. without any difficulties, and is quite
flexible.
A typical configuration will have LILO stop and print LILO: shortly
after you turn on your computer. It will then wait for a few seconds
for any optional input from the user, and failing that it will then
boot the default system. Typical system labels that people use in the
LILO configuration files are linux and backup and msdos. If you want
to type in a boot argument, you type it in here, after typing in the
system label that you want LILO to boot from, as shown in the example
below.
______________________________________________________________________
LILO: linux root=/dev/hda1
______________________________________________________________________
LILO comes with excellent documentation, and for the purposes of boot
args discussed here, the LILO append= command is of significant
importance when one wants to add a boot time argument as a permanent
addition to the LILO config file. You simply add something like
append = "foo=bar" to the /etc/lilo.conf file. It can either be added
at the top of the config file, making it apply to all sections, or to
a single system section by adding it inside an image= section. Please
see the LILO documentation for a more complete description.
2.2. LoadLin
The other commonly used Linux loader is `LoadLin' which is a DOS
program that has the capability to launch a Linux kernel from the DOS
prompt (with boot-args) assuming that certain resources are available.
This is good for people that use DOS and want to launch into Linux
from DOS.
It is also very useful if you have certain hardware which relies on
the supplied DOS driver to put the hardware into a known state. A
common example is `SoundBlaster Compatible' sound cards that require
the DOS driver to set a few proprietary 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.EXE avoids the reset of
the card that happens if one rebooted instead. Thus the card is left
in a SB compatible mode and hence is useable under Linux.
There are also other programs that can be used to boot Linux. For a
complete list, please look at the programs available on your local
Linux ftp mirror, under system/Linux-boot/.
2.3. The ``rdev'' utility
There are a few of the kernel boot parameters that have their default
values stored in various bytes in the kernel image itself. There is a
utility called rdev that is installed on most systems that knows where
these values are, and how to change them. It can also change things
that have no kernel boot argument equivalent, such as the default
video mode used.
The rdev utility is usually also aliased to swapdev, ramsize, vidmode
and rootflags. These are the five things that rdev can change, those
being the root device, the swap device, the RAM disk parameters, the
default video mode, and the readonly/readwrite setting of root device.
More information on rdev can be found by typing rdev -h or by reading
the supplied man page (man rdev).
2.4. How the Kernel Sorts the Arguments
Most of the boot args take the form of:
______________________________________________________________________
name[=value_1][,value_2]...[,value_11]
______________________________________________________________________
where `name' is a unique keyword that is used to identify what part of
the kernel the associated values (if any) are to be given to. Multiple
boot args are just a space separated list of the above format. Note
the limit of 11 is real, as the present code only handles 11 comma
separated parameters per keyword. (However, you can re-use the same
keyword with up to an additional 11 parameters in unusually
complicated situations, assuming the setup function supports it.)
Also note that the kernel splits the list into a maximum of ten
integer arguments, and a following string, so you can't really supply
11 integers unless you convert the 11th arg from a string to an int in
the driver itself.
Most of the sorting goes on in linux/init/main.c. First, the kernel
checks to see if the argument is any of the special arguments `root=',
`ro', `rw', or `debug'. The meaning of these special arguments is
described further on in the document.
Then it walks a list of setup functions (contained in the bootsetups
array) to see if the specified argument string (such as `foo') has
been associated with a setup function (foo_setup()) for a particular
device or part of the kernel. If you passed the kernel the line
foo=3,4,5,6,bar 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 integer
arguments 3, 4, 5 and 6 as given on the kernel command line, and also
hand it the string argument bar.
2.5. Setting Environment Variables.
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. An example would be to use TERM=vt100 or
BOOT_IMAGE=vmlinuz.bak as a boot argument. These environment
variables are typically tested for in the initialization scripts to
enable or disable a wide range of things.
2.6. Passing Arguments to the `init' program
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.
3. General Non-Device Specific Boot Args
These are the boot arguments that are not related to any specific
device or peripheral. They are instead related to certain internal
kernel parameters, such as memory handling, ramdisk handling, root
file system handling and others.
3.1. Root Filesystem options
The following options all pertain to how the kernel selects and
handles the root filesystem.
3.1.1. The `root=' Argument
This argument tells the kernel what device is to be used as the root
filesystem while booting. The default of this setting is the value of
the root device of the system that the kernel was built on. For
example, if the kernel in question was built on a system that used
`/dev/hda1' as the root partition, then the default root device would
be `/dev/hda1'. To override this default value, and select the second
floppy drive as the root device, one would use `root=/dev/fd1'.
Valid root devices are any of the following devices:
(1) /dev/hdaN to /dev/hddN, which is partition N on ST-506 compatible
disk `a to d'.
(2) /dev/sdaN to /dev/sdeN, which is partition N on SCSI compatible
disk `a to e'.
(3) /dev/xdaN to /dev/xdbN, which is partition N on XT compatible disk
`a to b'.
(4) /dev/fdN, which is floppy disk drive number N. Having N=0 would be
the DOS `A:' drive, and N=1 would be `B:'.
(5) /dev/nfs, which is not really a device, but rather a flag to tell
the kernel to get the root fs via the network.
(6) /dev/ram, which is the RAM disk.
The more awkward and less portable numeric specification of the above
possible disk 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.)
This is one of the few kernel boot arguments that has its default
stored in the kernel image, and which can thus be altered with the
rdev utility.
3.1.2. The `rootflags=' Argument
This option allows you to give options pertaining to the mounting of
the root filesystem just as you would to the mount program. An
example could be giving the noatime option to an ext2 fs.
3.1.3. The `rootfstype=' Argument
This option allows you to give a comma separated list of fs types that
will be tried for a match when trying to mount the root filesystem.
This list will be used instead of the internal default which usually
starts with ext2, minix and the like.
3.1.4. The `ro' Argument
When the kernel boots, it needs a root filesystem to read basic things
off of. This is the root filesystem that is mounted at boot. However,
if the root filesystem is mounted with write access, you can not
reliably check the filesystem integrity with half-written files in
progress. The `ro' option tells the kernel to mount the root
filesystem as `readonly' so that any filesystem consistency check
programs (fsck) can safely assume that there are no half-written files
in progress while performing the check. No programs or processes can
write to files on the filesystem in question until it is `remounted'
as read/write capable.
This is one of the few kernel boot arguments that has its default
stored in the kernel image, and which can thus be altered with the
rdev utility.
3.1.5. The `rw' Argument
This is the exact opposite of the above, in that it tells the kernel
to mount the root filesystem as read/write. The default is to mount
the root filesystem as read only. Do not run any `fsck' type programs
on a filesystem that is mounted read/write.
The same value stored in the image file mentioned above is also used
for this parameter, accessible via rdev.
3.1.6. The `nfsroot=' Argument
This argument tells the kernel which machine, what directory and what
NFS options to use for the root filesystem. Also note that the
argument root=/dev/nfs is required. Detailed information on using an
NFS root fs is in the file linux/Documentation/nfsroot.txt.
3.1.7. The `ip=' or `nfsaddrs=' Argument
If you are using NFS as a root filesystem, then there is no programs
like ifconfig and route present until the root fs is mounted, and so
the kernel has to configure the network interfaces directly. This
boot argument sets up the various network interface addresses that are
required to communicate over the network. If this argument is not
given, then the kernel tries to use RARP and/or BOOTP to figure out
these parameters.
3.2. Options Relating to RAM Disk Management
The following options all relate to how the kernel handles the RAM
disk device, which is usually used for bootstrapping machines during
the install phase, or for machines with modular drivers that need to
be installed to access the root filesystem.
3.2.1. The `ramdisk_start=' Argument
To allow a kernel image to reside on a floppy disk along with a
compressed ramdisk image, the `ramdisk_start=<offset>' command was
added. The kernel can't be included into the compressed ramdisk
filesystem image, because it needs to be stored starting at block zero
so that the BIOS can load the bootsector and then the kernel can
bootstrap itself to get going.
Note: If you are using an uncompressed ramdisk image, then the kernel
can be a part of the filesystem image that is being loaded into the
ramdisk, and the floppy can be booted with LILO, or the two can be
separate as is done for the compressed images.
If you are using a two-disk boot/root setup (kernel on disk 1, ramdisk
image on disk 2) then the ramdisk would start at block zero, and an
offset of zero would be used. Since this is the default value, you
would not need to actually use the command at all.
3.2.2. The `load_ramdisk=' Argument
This parameter tells the kernel whether it is to try to load a ramdisk
image or not. Specifying `load_ramdisk=1' will tell the kernel to load
a floppy into the ramdisk. The default value is zero, meaning that the
kernel should not try to load a ramdisk.
Please see the file linux/Documentation/ramdisk.txt for a complete
description of the new boot time arguments, and how to use them. A
description of how this parameter can be set and stored in the kernel
image via `rdev' is also described.
3.2.3. The `prompt_ramdisk=' Argument
This parameter tells the kernel whether or not to give you a prompt
asking you to insert the floppy containing the ramdisk image. In a
single floppy configuration the ramdisk image is on the same floppy as
the kernel that just finished loading/booting and so a prompt is not
needed. In this case one can use `prompt_ramdisk=0'. In a two floppy
configuration, you will need the chance to switch disks, and thus
`prompt_ramdisk=1' can be used. Since this is the default value, it
doesn't really need to be specified. ( (Historical note: Sneaky people
used to use the `vga=ask' LILO option to temporarily pause the boot
process and allow a chance to switch from boot to root floppy.)
Please see the file linux/Documentation/ramdisk.txt for a complete
description of the new boot time arguments, and how to use them. A
description of how this parameter can be set and stored in the kernel
image via `rdev' is also described.
3.2.4. The `ramdisk_size=' Argument
While it is true that the ramdisk grows dynamically as required, there
is an upper bound on its size so that it doesn't consume all available
RAM and leave you in a mess. The default is 4096 (i.e. 4MB) which
should be large enough for most needs. You can override the default to
a bigger or smaller size with this boot argument.
Please see the file linux/Documentation/ramdisk.txt for a complete
description of the new boot time arguments, and how to use them. A
description of how this parameter can be set and stored in the kernel
image via `rdev' is also described.
3.2.5. The `ramdisk_blocksize=' Argument
This can be tuned for better memory management behaviour. Quoting
from the ramdisk driver rd.c:
It would be very desirable to have a soft-blocksize (that in the case
of the ramdisk driver is also the hardblocksize ;) of PAGE_SIZE
because doing that we'll achieve a far better MM footprint. Using a
rd_blocksize of BLOCK_SIZE in the worst case we'll make
PAGE_SIZE/BLOCK_SIZE buffer-pages unfreeable. With a rd_blocksize of
PAGE_SIZE instead we are sure that only 1 page will be protected.
Depending on the size of the ramdisk you may want to change the
ramdisk blocksize to achieve a better or worse MM behaviour. The
default is still BLOCK_SIZE (needed by rd_load_image that supposes the
filesystem in the image uses a BLOCK_SIZE blocksize)
3.2.6. The `ramdisk=' Argument (obsolete)
(NOTE: This argument is obsolete, and should not be used except on
kernels v1.3.47 and older. The commands that should be used for the
ramdisk device are documented above. Newer kernels may accept this as
an alias for ramdisk_size.)
This specifies the size in kB of the RAM disk device. For example, if
one wished to have a root filesystem on a 1.44MB floppy loaded into
the RAM disk device, they would use:
______________________________________________________________________
ramdisk=1440
______________________________________________________________________
This is one of the few kernel boot arguments that has its default
stored in the kernel image, and which can thus be altered with the
rdev utility.
3.2.7. The `noinitrd' (initial RAM disk) Argument
The v2.x and newer kernels have a feature where the root filesystem
can be initially a RAM disk, and the kernel executes /linuxrc on that
RAM image. This feature is typically used to allow loading of modules
needed to mount the real root filesystem (e.g. load the SCSI driver
modules stored in the RAM disk image, and then mount the real root
filesystem on a SCSI disk.)
The actual `noinitrd' argument determines what happens to the initrd
data after the kernel has booted. When specified, instead of
converting it to a RAM disk, it is accessible via /dev/initrd, which
can be read once before the RAM is released back to the system. For
full details on using the initial RAM disk, please consult
linux/Documentation/initrd.txt. In addition, the most recent versions
of LILO and LOADLIN should have additional useful information.
3.3. Boot Arguments Related to Memory Handling
The following arguments alter how Linux detects or handles the
physical and virtual memory of your system.
3.3.1. The `cachesize=' Argument
Override level 2 CPU cache size detection (in kB). Sometimes CPU
hardware bugs make them report the cache size incorrectly. The kernel
will attempt work arounds to fix known problems, but for some CPUs it
is not possible to determine what the correct size should be. This
option provides an override for these situations.
3.3.2. The `mem=' Argument
This argument has several purposes: The original purpose was to
specify the amount of installed memory (or a value less than that if
you wanted to limit the amount of memory available to linux).
The next (and hardly used) purpose is to specify mem=nopentium which
tells the Linux kernel to not use the 4MB page table performance
feature. If you want to use it for both purposes, use a separate mem=
for each one.
The original 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. (Yes, another lack of foresight, just like the 1024
cylinder disks... sigh.) Linux uses this BIOS call at boot to
determine how much memory is installed. A newer specification (e820)
allows the BIOS to get this right on most machines nowadays. If you
have more than 64MB of RAM installed on an older machine, you can use
this boot argument to tell Linux how much memory you have. Here is a
quote from Linus on the 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'. 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.''
Note that the argument does not have to be in hex, and the suffixes
`k' and `M' (case insensitive) can be used to specify kilobytes and
Megabytes, respectively. (A `k' will cause a 10 bit shift on your
value, and a `M' will cause a 20 bit shift.) A typical example for a
128MB machine would be "mem=128m".
In some cases, the memory reported via e820 can also be wrong, and so
the mem=exactmap was added. You use this in conjunction with
specifying an exact memory map, such as:
______________________________________________________________________
mem=exactmap mem=640K@0 mem=1023M@1M
______________________________________________________________________
for a 1GB machine with the usual 384k of ISA memory mapped I/O space
excluded from use.
3.3.3. The `memfrac=' Argument
Memory is broken down into zones; on i386 these zones correspond to
`DMA' (for legacy ISA devices that can only address up to 16MB via
DMA); `Normal' for memory from 16MB up to 1GB, and `HighMem' for
memory beyond 1GB (assuming your kernel was built with high mem
support enabled). The two (or three) integers supplied here determine
how much memory in each zone should be kept free - with the size of
the zone divided by the number supplied being used as the minimum (so
smaller numbers mean keep more free in the zone). The defaults are
currently memfrac=32,128,128.
3.3.4. The `swap=' Argument
This allows the user to tune some of the virtual memory (VM)
parameters that are related to swapping to disk. It accepts the
following eight parameters:
______________________________________________________________________
MAX_PAGE_AGE
PAGE_ADVANCE
PAGE_DECLINE
PAGE_INITIAL_AGE
AGE_CLUSTER_FRACT
AGE_CLUSTER_MIN
PAGEOUT_WEIGHT
BUFFEROUT_WEIGHT
______________________________________________________________________
Interested hackers are advised to have a read of linux/mm/swap.c and
also make note of the goodies in /proc/sys/vm. Kernels come with some
useful documentation on this in the linux/Documentation/vm/ directory.
3.3.5. The `buff=' Argument
Similar to the `swap=' argument, this allows the user to tune some of
the parameters related to buffer memory management. It accepts the
following six parameters:
______________________________________________________________________
MAX_BUFF_AGE
BUFF_ADVANCE
BUFF_DECLINE
BUFF_INITIAL_AGE
BUFFEROUT_WEIGHT
BUFFERMEM_GRACE
______________________________________________________________________
Interested hackers are advised to have a read of linux/mm/swap.c and
also make note of the goodies in /proc/sys/vm. Kernels come with some
useful documentation on this in the linux/Documentation/vm/ directory.
3.4. Other Misc. Kernel Boot Arguments
These various boot arguments let the user tune certain internal kernel
parameters.
3.4.1. The `acpi=' Argument
Currently this only accepts `off' to disable the ACPI subsystem.
3.4.2. The `console=' Argument
Usually the console is the 1st virtual terminal, and so boot messages
appear on your VGA screen. Sometimes it is nice to be able to use
another device like a serial port (or even a printer!) to be the
console when no video device is present. It is also useful to capture
boot time messages if a problem stops progress before they can be
logged to disk. An example would be to use console=ttyS1,9600 for
selecting the 2nd serial port at 9600 baud to be the console. More
information can be found in linux/Documentation/serial-console.txt.
3.4.3. The `debug' Argument
The kernel communicates important (and not-so important) messages to
the operator via the printk() function. If the message is considered
important, the printk() function will put a copy on the present
console as well as handing it off to the klogd() facility so that it
gets logged to disk. The reason for printing important messages to the
console as well as logging them to disk is because under unfortunate
circumstances (e.g. a disk failure) the message won't make it to disk
and will be lost.
The threshold for what is and what isn't considered important is set
by the console_loglevel variable. The default is to log anything more
important than DEBUG (level 7) to the console. (These levels are
defined in the include file kernel.h) Specifying debug as a boot
argument will set the console loglevel to 10, so that all kernel
messages appear on the console.
The console loglevel can usually also be set at run time via an option
to the klogd() program. Check the man page for the version installed
on your system to see how to do this.
3.4.4. The `decnet=' Argument
If you are using DECnet, you can supply two comma separated integers
here to give your area and node respectively.
3.4.5. The `devfs=' Argument
If you are using devfs, instead of the standard static devices in
/dev/ then you can supply the words only or mount with this argument.
There are also additional debug arguments that are listed in the
source.
3.4.6. The `gpt' Argument
If you are using EFI GUID Partition Table handling, you can use this
to override problems associated with an invalid PMBR.
3.4.7. The `idle=' Argument
Setting this to `poll' causes the idle loop in the kernel to poll on
the need reschedule flag instead of waiting for an interrupt to
happen. This can result in an improvement in performance on SMP
systems (albeit at the cost of an increase in power consumption).
3.4.8. The `init=' Argument
The kernel defaults to starting the `init' program at boot, which then
takes care of setting up the computer for users via launching getty
programs, running `rc' scripts and the like. The kernel first looks
for /sbin/init, then /etc/init (depreciated), and as a last resort, it
will try to use /bin/sh (possibly on /etc/rc). If for example, your
init program got corrupted and thus stopped you from being able to
boot, you could simply use the boot prompt init=/bin/sh which would
drop you directly into a shell at boot, allowing you to replace the
corrupted program.
3.4.9. The `isapnp=' Argument
This takes the form of: isapnp=read_port,reset,skip_pci_scan,verbose
3.4.10. The `isapnp_reserve_dma=' Argument
This takes the form of: isapnp_reserve_dma=n1,n2,n3,...nN where n1 ...
nN are the DMA channel numbers to not use for PnP.
3.4.11. The `isapnp_reserve_io=' Argument
This takes the form of:
isapnp_reserve_irq=io1,size1,io2,size2,...ioN,sizeN where ioX,sizeX
are I/O start and length pairs of regions in I/O space that are not to
be used by PnP.
3.4.12. The `isapnp_reserve_irq=' Argument
This takes the form of: isapnp_reserve_irq=n1,n2,n3,...nN where n1 ...
nN are the interrupt numbers to not use for PnP.
3.4.13. The `isapnp_reserve_mem=' Argument
This takes the form of:
isapnp_reserve_mem=mem1,size1,mem2,size2,...memN,sizeN where ioX,sizeX
are I/O start and length pairs of regions in memory space that are not
to be used by PnP.
3.4.14. The `kbd-reset' Argument
Normally on i386 based machines, the Linux kernel does not reset the
keyboard controller at boot, since the BIOS is supposed to do this.
But as usual, not all machines do what they should. Supplying this
option may help if you are having problems with your keyboard
behaviour. It simply forces a reset at initialization time. (Some
have argued that this should be the default behaviour anyways).
3.4.15. The `lockd.udpport=' and `lockd.tcpport' Argument
These tell the kernel to use the given port numbers for NFS lockd
operation (for either UDP or TCP operation).
3.4.16. The `maxcpus=' Argument
The number given with this argument limits the maximum number of CPUs
activated in SMP mode. Using a value of 0 is equivalent to the nosmp
option.
3.4.17. The `mca-pentium' Argument
The IBM model 95 Microchannel machines seem to lock up on the test
that Linux usually does to detect the type of math chip coupling.
Since all Pentium chips have a built in math processor, this test (and
the lock up problem) can be avoided by using this boot option.
3.4.18. The `md=' Argument
If your root filesystem is on a Multiple Device then you can use this
(assuming you compiled in boot support) to tell the kernel the
multiple device layout. The format (from the file
linux/Documentation/md.txt) is:
md=md_device_num,raid_level,chunk_size_factor,fault_level,dev0,dev1,...,devN
Where md_device_num is the number of the md device, i.e. 0 means md0,
1 means md1, etc. For raid_level, use -1 for linear mode and 0 for
striped mode. Other modes are currently unsupported. The
chunk_size_factor is for raid-0 and raid-1 only and sets the chunk
size as PAGE_SIZE shifted left the specified amount. The fault_level
is only for raid-1 and sets the maximum fault number to the specified
number. (Currently unsupported due to lack of boot support for
raid1.) The dev0-devN are a comma separated list of the devices that
make up the individual md device: e.g. /dev/hda1,/dev/hdc1,/dev/sda1
See also raid=.
3.4.19. The `nmi_watchdog=' Argument
Supplying a non-zero integer will enable the non maskable interrupt
watchdog (assuming IO APIC support is compiled in). This checks to
see if the interrupt count is increasing (indicating normal system
activity) and if it is not then it assumes that a processor is stuck
and forces an error dump of diagnostic information.
3.4.20. The `no387' Argument
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,
apparently due to a bug in the FRSAV/FRRESTOR instructions. Using the
`no387' boot argument causes Linux to ignore the math coprocessor even
if you have one. Of course you must then have your kernel compiled
with math emulation support! This may also be useful if you have one
of those really old 386 machines that could use an 80287 FPU, as Linux
can't use an 80287.
3.4.21. The `no-hlt' Argument
The i386 (and successors thereof) family of CPUs have a `hlt'
instruction which tells the CPU that nothing is going to happen until
an external device (keyboard, modem, disk, etc.) calls upon the CPU to
do a task. This allows the CPU to enter a `low-power' mode where it
sits like a zombie until an external device wakes it up (usually via
an interrupt). Some of the early i486DX-100 chips had a problem with
the `hlt' instruction, in that they couldn't reliably return to
operating mode after this instruction was 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 your CPU when there is no
activity. This allows people with these broken chips to use Linux,
although they would be well advised to seek a replacement through a
warranty where possible.
3.4.22. The `no-scroll' Argument
Using this argument at boot disables scrolling features that make it
difficult to use Braille terminals.
3.4.23. The `noapic' Argument
Using this option tells a SMP kernel to not use some of the advanced
features of the interrupt controller on multi processor machines. Use
of this option may be required when a device (such as those using
ne2k-pci or 3c59xi drivers) stops generating interrupts (i.e. cat
/proc/interrupts shows the same interrupt count.) See
linux/Documentation/IO-APIC.txt for more information.
3.4.24. The `noht' Argument
This will disable hyper-threading on intel processors that have this
feature.
3.4.25. The `noisapnp' Argument
If ISA PnP is built into the kernel, this will disable it.
3.4.26. The `nomce' Argument
Some newer processors have the ability to self-monitor and detect
inconsistencies that should not regularly happen. If an inconsistency
is detected, a Machine Check Exception will take place and the system
will be halted (rather than plundering forward and corrupting your
data). You can use this argument to disable this feature, but be sure
to check that your CPU is not overheating or otherwise faulty first.
3.4.27. The `nosmp' Argument
Use of this option will tell a SMP kernel on a SMP machine to operate
single processor. Typically only used for debugging and determining
if a particular problem is SMP related.
3.4.28. The `noresume' Argument
If software suspend is enabled, and a suspend to disk file has been
specified, using this argument will give a normal boot and the suspend
data will be ignored.
3.4.29. The `notsc' Argument
Use of this option will tell the kernel to not use the Time Stamp
Counter for anything, even if the CPU has one.
3.4.30. The `nofxsr" Argument
Use of this option will tell the kernel to not use any speed-up tricks
involving the floating point unit, even if the processor supports
them.
3.4.31. The `panic=' Argument
In the unlikely event of a kernel panic (i.e. an internal error that
has been detected by the kernel, and which the kernel decides is
serious enough to moan loudly and then halt everything), the default
behaviour is to just sit there until someone comes along and notices
the panic message on the screen and reboots the machine. However if a
machine is running unattended in an isolated location it may be
desirable for it to automatically reset itself so that the machine
comes back on line. For example, using panic=30 at boot would cause
the kernel to try and reboot itself 30 seconds after the kernel panic
happened. A value of zero gives the default behaviour, which is to
wait forever.
Note that this timeout value can also be read and set via the
/proc/sys/kernel/panic sysctl interface.
3.4.32. The `pirq=' Argument
Using this option tells a SMP kernel information on the PCI slot
versus IRQ settings for SMP motherboards which are unknown (or known
to be blacklisted). See linux/Documentation/IO-APIC.txt for more
information.
3.4.33. The `profile=' Argument
Kernel developers can profile how and where the kernel is spending its
CPU cycles in an effort to maximize efficiency and performance. This
option lets you set the profile shift count at boot. Typically it is
set to two. You need a tool such as readprofile.c that can make use
of the /proc/profile output.
3.4.34. The `quiet' Argument
This is pretty much the opposite of the `debug' argument. When this
is given, only important and system critical kernel messages are
printed to the console. Normal messages about hardware detection at
boot are suppressed.
3.4.35. The `raid=' Argument
Accepts noautodetect at the moment. See also md=.
3.4.36. The `reboot=' Argument
This option controls the type of reboot that Linux will do when it
resets the computer (typically via /sbin/init handling a Control-Alt-
Delete). The default as of v2.0 kernels is to do a `cold' reboot (i.e.
full reset, BIOS does memory check, etc.) instead of a `warm' reboot
(i.e. no full reset, no memory check). It was changed to be cold by
default since that tends to work on cheap/broken hardware that fails
to reboot when a warm reboot is requested. To get the old behaviour
(i.e. warm reboots) use reboot=w or in fact any word that starts with
w will work.
Other accepted options are `c', `b', `h', and `s', for cold, bios,
hard, and SMP respectively. The `s' takes an optional digit to specify
which CPU should handle the reboot. Options can be combined where it
makes sense, i.e. reboot=b,s2
3.4.37. The `reserve=' Argument
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 poorly designed hardware that causes the boot to freeze
(such as some ethercards), hardware that is mistakenly identified,
hardware whose state is changed by an earlier probe, or merely
hardware you don't want the kernel to initialize.
The reserve boot-time argument addresses this problem by specifying an
I/O port region that shouldn't be probed. That region is reserved in
the kernel's port registration table as if a device has already been
found in that region (with the name reserved). Note that this
mechanism shouldn't be necessary on most machines. Only when there is
a problem or special case would it be necessary to use this.
The I/O ports in the specified region are protected against device
probes that do a check_region() prior to probing blindly into a region
of I/O space. This was put in to be used when some driver was hanging
on a NE2000, or misidentifying some other device as its own. A
correct device driver shouldn't probe a reserved region, unless
another boot argument explicitly specifies that it do so. This
implies that reserve will most often be used with some other boot
argument. Hence if you specify a reserve region to protect a specific
device, you must generally specify an explicit probe for that device.
Most drivers ignore the port registration table if they are given an
explicit address.
For example, the boot line
______________________________________________________________________
reserve=0x300,32 blah=0x300
______________________________________________________________________
keeps all device drivers except the driver for `blah' from probing
0x300-0x31f.
As usual with boot-time specifiers there is an 11 parameter limit,
thus you can only specify 5 reserved regions per reserve keyword.
Multiple reserve specifiers will work if you have an unusually
complicated request.
3.4.38. The `resume=' Argument
If you are using software suspend, then this will allow you to specify
the file name of the suspend to disk data that you want the machine to
resume from.
3.4.39. The `vga=' Argument
Note that this is not really a boot argument. It is an option that is
interpreted by LILO and not by the kernel like all the other boot
arguments are. However its use has become so common that it deserves a
mention here. It can also be set via using rdev -v or equivalently
vidmode on the vmlinuz file. This allows the setup code to use the
video BIOS to change the default display mode before actually booting
the Linux kernel. Typical modes are 80x50, 132x44 and so on. The best
way to use this option is to start with vga=ask which will prompt you
with a list of various modes that you can use with your video adapter
before booting the kernel. Once you have the number from the above
list that you want to use, you can later put it in place of the `ask'.
For more information, please see the file linux/Documentation/svga.txt
that comes with all recent kernel versions.
Note that newer kernels (v2.1 and up) have the setup code that changes
the video mode as an option, listed as Video mode selection support so
you need to enable this option if you want to use this feature.
4. Boot Arguments to Control PCI Bus Behaviour (`pci=')
The `pci=' argument (not avail. in v2.0 kernels) can be used to change
the behaviour of PCI bus device probing and device behaviour. Firstly
the file linux/drivers/pci/pci.c checks for architecture independent
pci= options. The remaining allowed arguments are handled in
linux/arch/???/kernel/bios32.c and are listed below for ???=i386.
4.1. The `pci=assign-busses' Argument
This tells the kernel to always assign all PCI bus numbers, overriding
whatever the firmware may have done.
4.2. The `pci=bios' and `pci=nobios' Arguments
These are used to set/clear the flag indicating that the PCI probing
is to take place via the PCI BIOS. The default is to use the BIOS.
4.3. The `pci=conf1' and `pci=conf2' Arguments
If PCI direct mode is enabled, the use of these enables either
configuration Type 1 or Type 2. These implicitly clear the PCI BIOS
probe flag (i.e. `pci=nobios') too.
4.4. The `pci=irqmask=' Argument
This allows the user to supply an IRQ mask value, which is converted
using strtol(). It will set a bit mask of IRQs allowed to be assigned
automatically to PCI devices. You can make the kernel exclude IRQs of
your ISA cards this way.
4.5. The `pci=lastbus=' Argument
This allows the user to supply a lastbus value, which is converted
using strtol(). It will scan all buses till bus N. Can be useful if
the kernel is unable to find your secondary buses and you want to tell
it explicitly which ones they are.
4.6. The `pci=noacpi' Argument
This disables the use of ACPI routing information during the PCI
configuration stages.
4.7. The `pci=nopeer' Argument
This disables the default peer bridge fixup, which according to the
source does the following:
``In case there are peer host bridges, scan bus behind each of them.
Although several sources claim that the host bridges should have
header type 1 and be assigned a bus number as for PCI2PCI bridges, the
reality doesn't pass this test and the bus number is usually set by
BIOS to the first free value.''
4.8. The `pci=nosort' Argument
Using this argument instructs the kernel to not sort the PCI devices
during the probing phase.
4.9. The `pci=off' Argument
Using this option disables all PCI bus probing. Any device drivers
that make use of PCI functions to find and initialize hardware will
most likely fail to work.
4.10. The `pci=usepirqmask' Argument
This sets the USE_PIRQ_MASK flag during PCI init. The kernel will
honour the possible IRQ mask stored in the BIOS PIR table. This is
needed on some systems with broken BIOSes, notably some HP Pavilion
N5400 and Omnibook XE3 notebooks. This will have no effect if ACPI IRQ
routing is enabled.
4.11. The `pci=rom' Argument
This sets the ASSIGN_ROM flag during the probing phase. The kernel
will assign address space to expansion ROMs. Use with caution as
certain devices share address decoders between ROMs and other
resources.
5. Boot Arguments for Video Frame Buffer Drivers
The `video=' argument (not avail. in v2.0 kernels) is used when the
frame buffer device abstraction layer is built into the kernel. If
that sounds complicated, well it isn't really too bad. It basically
means that instead of having a different video program (the X11R6
server) for each brand of video card (e.g. XF86_S3, XF86_SVGA, ...),
the kernel would have a built in driver available for each video card
and export a single interface for the video program so that only one
X11R6 server (XF86_FBDev) would be required. This is similar to how
networking is now - the kernel has drivers available for each brand of
network card and exports a single network interface so that just one
version of a network program (like Netscape) will work for all
systems, regardless of the underlying brand of network card.
The typical format of this argument is video=name:option1,option2,...
where name is the name of a generic option or of a frame buffer
driver. The video= option is passed from linux/init/main.c into
linux/drivers/video/fbmem.c for further processing. Here it is
checked for some generic options before trying to match to a known
driver name. Once a driver name match is made, the comma separated
option list is then passed into that particular driver for final
processing. The list of valid driver names can be found by reading
down the fb_drivers array in the file fbmem.c mentioned above.
Information on the options that each driver supports will eventually
be found in linux/Documentation/fb/ but currently (v2.2) only a few
are described there. Unfortunately the number of video drivers and
the number of options for each one is content for another document
itself and hence too much to list here.
If there is no Documentation file for your card, you will have to get
the option information directly from the driver. Go to
linux/drivers/video/ and look in the appropriate ???fb.c file (the ???
will be based on the card name). In there, search for a function with
_setup in its name and you should see what options the driver tries to
match, such as font or mode or...
5.1. The `video=map:...' Argument
This option is used to set/override the console to frame buffer device
mapping. A comma separated list of numbers sets the mapping, with the
value of option N taken to be the frame buffer device number for
console N.
5.2. The `video=scrollback:...' Argument
A number after the colon will set the size of memory allocated for the
scrollback buffer. (Use Shift and Page Up or Page Down keys to
scroll.) A suffix of `k' or `K' after the number will indicate that
the number is to be interpreted as kilobytes instead of bytes.
5.3. The `video=vc:...' Argument
A number, or a range of numbers (e.g. video=vc:2-5) will specify the
first, or the first and last frame buffer virtual console(s). The use
of this option also has the effect of setting the frame buffer console
to not be the default console.
6. Boot Arguments for SCSI Peripherals.
This section contains the descriptions of the boot args that are used
for passing information about the installed SCSI host adapters, and
SCSI devices.
6.1. Arguments for Upper and Mid-level Drivers
The upper level drivers handle all things SCSI, regardless of whether
they be disk, tape, or CD-ROM. The mid level drivers handle things
like disks, CD-ROMs and tapes without getting into low level host
adapter device driver specifics.
6.1.1. Maximum Probed LUNs (`max_scsi_luns=')
Each SCSI device can have a number of `sub-devices' contained within
itself. The most common example is any of the 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.
The problem arises with single LUN devices with bad firmware. Some
poorly designed SCSI devices (old and unfortunately new) can not
handle being probed for LUNs not equal to zero. They will respond by
locking up, and possibly taking the whole SCSI bus down with them.
The kernel has a configuration option that allows you to set the
maximum number of probed LUNs. The default is to only probe LUN zero,
to avoid the problem described above.
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
6.1.2. SCSI Logging (`scsi_logging=')
Supplying a non-zero value to this boot argument turns on logging of
all SCSI events (error, scan, mlqueue, mlcomplete, llqueue,
llcomplete, hlqueue, hlcomplete). Note that better control of which
events are logged can be obtained via the /proc/scsi/scsi interface if
you aren't interested in the events that take place at boot before the
/proc/ filesystem is accessible.
6.1.3. Parameters for the SCSI Tape Driver (`st=')
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.
6.2. Arguments for SCSI Host Adapter Drivers
These are arguments for low level SCSI host device drivers, and as
such are typically only used by those that compile their own kernel
with the SCSI driver built in. These people are advised to check the
source for the latest list of options that can be supplied to their
driver.
aha152x= Adaptec aha151x, aha152x, aic6260, aic6360, SB16-SCSI
aha1542= Adaptec aha1540, aha1542
aic7xxx= Adaptec aha274x, aha284x, aic7xxx
advansys= AdvanSys SCSI Host Adaptors
in2000= Always IN2000 Host Adaptor
AM53C974= AMD AM53C974 based hardware
BusLogic= ISA/PCI/EISA BusLogic SCSI Hosts
eata= EATA SCSI Cards
tmc8xx= Future Domain TMC-8xx, TMC-950
fdomain= Future Domain TMC-16xx, TMC-3260, AHA-2920
ppa= IOMEGA Parallel Port / ZIP drive
ncr5380= NCR5380 based controllers
ncr53c400= NCR53c400 based controllers
ncr53c406a= NCR53c406a based controllers
pas16= Pro Audio Spectrum
st0x= Seagate ST-0x
t128= Trantor T128
u14-34f= Ultrastor SCSI cards
wd7000= Western Digital WD7000 cards
7. Hard Disks
This section lists all the boot args associated with standard MFM/RLL,
ST-506, XT, and IDE disk drive devices. Note that both the IDE and
the generic ST-506 HD driver both accept the `hd=' option.
7.1. IDE Disk/CD-ROM Driver Parameters
The IDE driver accepts a number of parameters, which range from disk
geometry specifications, to support for advanced or broken controller
chips. The following is a summary of some of the more common boot
arguments. For full details, you really should consult the file
ide.txt in the linux/Documentation directory, from which this summary
was extracted.
______________________________________________________________________
"hdx=" is recognized for all "x" from "a" to "h", such as "hdc".
"idex=" is recognized for all "x" from "0" to "3", such as "ide1".
"hdx=noprobe" : drive may be present, but do not probe for it
"hdx=none" : drive is NOT present, ignore cmos and do not probe
"hdx=nowerr" : ignore the WRERR_STAT bit on this drive
"hdx=cdrom" : drive is present, and is a cdrom drive
"hdx=cyl,head,sect" : disk drive is present, with specified geometry
"hdx=autotune" : driver will attempt to tune interface speed
to the fastest PIO mode supported,
if possible for this drive only.
Not fully supported by all chipset types,
and quite likely to cause trouble with
older/odd IDE drives.
"idex=noprobe" : do not attempt to access/use this interface
"idex=base" : probe for an interface at the addr specified,
where "base" is usually 0x1f0 or 0x170
and "ctl" is assumed to be "base"+0x206
"idex=base,ctl" : specify both base and ctl
"idex=base,ctl,irq" : specify base, ctl, and irq number
"idex=autotune" : driver will attempt to tune interface speed
to the fastest PIO mode supported,
for all drives on this interface.
Not fully supported by all chipset types,
and quite likely to cause trouble with
older/odd IDE drives.
"idex=noautotune" : driver will NOT attempt to tune interface speed
This is the default for most chipsets,
except the cmd640.
"idex=serialize" : do not overlap operations on idex and ide(x^1)
______________________________________________________________________
The following are valid ONLY on ide0, and the defaults for the
base,ctl ports must not be altered.
______________________________________________________________________
"ide0=dtc2278" : probe/support DTC2278 interface
"ide0=ht6560b" : probe/support HT6560B interface
"ide0=cmd640_vlb" : *REQUIRED* for VLB cards with the CMD640 chip
(not for PCI -- automatically detected)
"ide0=qd6580" : probe/support qd6580 interface
"ide0=ali14xx" : probe/support ali14xx chipsets (ALI M1439/M1445)
"ide0=umc8672" : probe/support umc8672 chipsets
______________________________________________________________________
During the install of some PCMCIA systems, you may be able to get
detection of your CD-ROM by using:
______________________________________________________________________
"ide2=0x180,0x386" : probe typical PCMCIA IDE interface location
______________________________________________________________________
Everything else is rejected with a "BAD OPTION" message. Also note
that there is an implied ide0=0x1f0 ide1=0x170 in the absence of any
other ide boot args.
7.2. Old MFM/RLL/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=', `hdb='
and so on are not valid here. The format is as follows:
______________________________________________________________________
hd=cyls,heads,sects
______________________________________________________________________
If there are two disks installed, the above is repeated with the
geometry parameters of the second disk.
7.3. XT Disk Driver Options (`xd=', `xd_geo=')
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. The
probe code for these cards looks for an installed BIOS, and if none is
present, the probe will not find your card. Or, if the signature
string of your BIOS is not recognized then it will also not be found.
In either case, you will then have to use a boot argument of the form:
______________________________________________________________________
xd=type,irq,iobase,dma_chan
______________________________________________________________________
The type value specifies the particular manufacturer of the card, and
are as follows: 0=generic; 1=DTC; 2,3,4=Western Digital,
5,6,7=Seagate; 8=OMTI. The only difference between multiple types from
the same manufacturer is the BIOS string used for detection, which is
not used if the type is specified.
The xd_setup() function does no checking on the values, and assumes
that you entered all four values. Don't 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
______________________________________________________________________
If the disk geometry that the kernel prints out comes out all wrong to
what you know the disk is set up as, you can override that as well,
with:
______________________________________________________________________
xd_geo=cyl_xda,head_xda,sec_xda
______________________________________________________________________
Add another comma and another three CHS values if you are silly enough
to have two disks on the old hunk of scrap...
8. The Sound Drivers
Note that there was a rewrite of a lot of the sound core and related
drivers. The older stuff is generally called `OSS' and the newer is
called `ALSA'. The intention is to drop the OSS stuff eventually. To
avoid name conflict, the ALSA stuff generally has `snd-' as a prefix
to all the boot parameters.
Note that each driver has its own individual boot argument (very old
kernels used a shared sound=). Also, generally no defaults are set at
compile time (i.e. you must supply a boot argument for older non-PNP
ISA cards to be detected.) Your best source of information for your
card is the files in linux/Documentation/sound/.
8.1. Individual Sound Device Driver Arguments
8.1.1. ALSA ISA drivers
snd-dummy= Dummy soundcard
snd-mpu401= mpu401 UART
snd-mtpav= MOTU Midi Timepiece
snd-serial= Serial UART 16450/16550 MIDI
snd-virmidi= Dummy soundcard for virtual rawmidi devices
snd-ad1816a= ADI SoundPort AD1816A
snd-ad1848= Generic driver for AD1848/AD1847/CS4248
snd-als100= Avance Logic ALS100
snd-azt2320= Aztech Systems AZT2320 (and 2316)
snd-cmi8330= C-Media's CMI8330
snd-cs4231= Generic driver for CS4231 chips
snd-cs4232= Generic driver for CS4232 chips
snd-cs4236= Generic driver for CS4235/6/7/8/9 chips
snd-dt019x= Diamond Technologies DT-019x
snd-es1688= Generic ESS AudioDrive ESx688
snd-es18xx= Generic ESS AudioDrive ES18xx
snd-gusclassic= Gus classic
snd-gusextreme= Gus extreme
snd-gusmax= Gus Max
snd-interwave= Interwave
snd-interwave-stb= Interwave
snd-opl3sa2= Yamaha OPL3SA2
snd-opti93x= OPTi 82c93x based cards
snd-opti92x-cs4231= OPTi 82c92x/CS4231
snd-opti92x-ad1848= OPTi 82c92x/AD1848
snd-es968= ESS AudioDrive ES968
snd-sb16= SoundBlaster 16
snd-sbawe= SoundBlaster 16 AWE
snd-sb8= Old 8 bit SoundBlaster (1.0, 2.0, Pro)
snd-sgalaxy= Sound galaxy
snd-wavefront= Wavefront
8.1.2. OSS drivers
ad1848= AD1848
adlib= Adlib
mad16= MAD16
pas2= ProAudioSpectrum PAS16
sb= SoundBlaster
uart401= UART 401 (on card chip)
uart6850= UART 6850 (on card chip)
opl3= Yamaha OPL2/OPL3/OPL4 FM Synthesizer (on card chip)
opl3sa= Yamaha OPL3-SA FM Synthesizer (on card chip)
opl3sa2= Yamaha OPL3-SA2/SA3 FM Synthesizer (on card chip)
8.1.3. ALSA PCI Drivers
snd-ali5451= ALi PCI audio M5451
snd-als4000= Avance Logic ALS4000
snd-cmipci= C-Media CMI8338 and 8738
snd-cs4281= Cirrus Logic CS4281
snd-cs46xx= Cirrus Logic Sound Fusion CS46XX
snd-emu10k1= EMU10K1 (SB Live!)
snd-ens1370= Ensoniq ES1370 AudioPCI
snd-ens1371= Ensoniq ES1371 AudioPCI
snd-es1938= ESS Solo-1 (ES1938, ES1946, ES1969)
snd-es1968= ESS Maestro 1/2/2E
snd-fm801= ForteMedia FM801
snd-intel8x0= Intel ICH (i8x0) chipsets
snd-maestro3= ESS Maestro3/Allegro (ES1988)
snd-korg1212= Korg 1212 IO
snd-rme32= RME Digi32, Digi32/8 and Digi32 PRO
snd-nm256= NeoMagic 256AV and 256ZX
snd-rme96= RME Digi96, Digi96/8 and Digi96/8 PRO/PAD/PST
snd-rme9652= RME Digi9652 audio interface
snd-hdsp= RME Hammerfall DSP
snd-sonicvibes= S3 SonicVibes
snd-trident= Trident 4DWave DX/NX & SiS SI7018
snd-via82xx= VIA South Bridge VT82C686A/B/C, VT8233A/C, VT8235
snd-ymfpci= Yamaha DS1/DS1E
snd-ice1712= ICEnsemble ICE1712 (Envy24)
9. CD-ROMs (Non-SCSI/ATAPI/IDE)
This section lists all the possible boot args pertaining to these
older CD-ROM devices on proprietary interface cards. Note that this
does not include SCSI or IDE/ATAPI CD-ROMs. See the appropriate
section(s) for those types of CD-ROMs.
Note that most of these CD-ROMs have documentation files that you
should read, and they are all in one handy place:
linux/Documentation/cdrom.
9.1. Old CD-ROM Driver Arguments
aztcd= Aztech Interface
cdu31a= CDU-31A and CDU-33A Sony Interface (Also Old PAS)
sonycd535= CDU-535 Sony Interface
gscd= GoldStar Interface
isp16= ISP16 Interface
mcd= Mitsumi Standard Interface
mcdx= Mitsumi XA/MultiSession Interface
optcd= Optics Storage Interface
cm206= Phillips CM206 Interface
sjcd= Sanyo Interface
sbpcd= SoundBlaster Pro Interface
10. Serial and ISDN Drivers
10.1. The ISDN drivers
Please see linux/Documentation/isdn/ for the full details of all the
options the following ISDN drivers accept.
icn= ICN ISDN driver
pcbit= PCBIT ISDN driver
teles= Teles ISDN driver
10.2. The Serial drivers
Please see linux/Documentation/ and/or the README files in
linux/drivers/char for the full details of all the options that the
following support.
digi= DigiBoard Driver
riscom8= RISCom/8 Multiport Serial Driver
baycom= Baycom Serial/Parallel Radio Modem
11. Other Hardware Devices
Any other devices that didn't fit into any of the above categories got
lumped together here.
11.1. Ethernet Devices (`ether=', `netdev=')
Different drivers make use of different parameters, but they all at
least share having an IRQ, an I/O port base value, and a name. In its
most generic form, it looks something like this:
______________________________________________________________________
ether=irq,iobase[,param_1[,param_2,...param_8]]],name
______________________________________________________________________
The first non-numeric argument is taken as the name. The param_n
values (if applicable) usually have different meanings for each
different card/driver. Typical param_n values are used to specify
things like shared memory address, interface selection, DMA channel
and the like.
The most common use of this parameter is to force probing for a second
ethercard, as the default is to only probe for one (with 2.4 and older
kernels). 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.
IMPORTANT NOTE TO MODULE USERS: The above will not force a probe for a
second card if you are using the driver(s) as run time loadable
modules (instead of having them complied into the kernel). Most Linux
distributions use a bare bones kernel combined with a large selection
of modular drivers. The ether= only applies to drivers compiled
directly into the kernel.
The Ethernet-HowTo has complete and 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 for more complete
information. Ethernet-HowTo
<http://metalab.unc.edu/mdw/HOWTO/Ethernet-HOWTO.html>
11.2. The Floppy Disk Driver (`floppy=')
There are many floppy driver options, and they are all listed in
floppy.txt in linux/Documentation. There are too many options in that
file to list here. Instead, only those options that may be required to
get a Linux install to proceed on less than normal hardware are
reprinted here.
floppy=0,daring Tells the floppy driver that your floppy controller
should be used with caution (disables all daring operations).
floppy=thinkpad Tells the floppy driver that you have a Thinkpad.
Thinkpads use an inverted convention for the disk change line.
floppy=nodma Tells the floppy driver not to use DMA for data
transfers. This is needed on HP Omnibooks, which don't have a
workable DMA channel for the floppy driver. This option is also useful
if you frequently get `Unable to allocate DMA memory' messages. Use
of `nodma' is not recommended if you have a FDC without a FIFO (8272A
or 82072). 82072A and later are OK). The FDC model is reported at
boot. You also need at least a 486 to use nodma.
floppy=nofifo Disables the FIFO entirely. This is needed if you get
`Bus master arbitration error' messages from your Ethernet card (or
from other devices) while accessing the floppy.
floppy=broken_dcl Don't use the disk change line, but assume that the
disk was changed whenever the device node is reopened. Needed on some
boxes where the disk change line is broken or unsupported. This
should be regarded as a stopgap measure, indeed it makes floppy
operation less efficient due to unneeded cache flushings, and slightly
more unreliable. Please verify your cable connection and jumper
settings if you have any DCL problems. However, some older drives, and
also some Laptops are known not to have a DCL.
floppy=debug Print (additional) debugging messages.
floppy=messages Print informational messages for some operations (disk
change notifications, warnings about over and underruns, and about
autodetection).
11.3. The Bus Mouse Driver (`bmouse=')
The busmouse driver only accepts one parameter, that being the
hardware IRQ value to be used.
11.4. The MS Bus Mouse Driver (`msmouse=')
The MS mouse driver only accepts one parameter, that being the
hardware IRQ value to be used.
11.5. The Printer Driver (`lp=')
With this boot argument 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 i/o, IRQ pairs. For example,
lp=0x3bc,0,0x378,7 would use the port at 0x3bc in IRQ-less (polling)
mode, and use IRQ 7 for the port at 0x378. The port at 0x278 (if any)
would not be probed, since autoprobing only takes place in the absence
of a lp= argument. To disable the printer driver entirely, one can use
lp=0.
11.6. The Parallel port IP driver (`plip=')
Using plip=timid will tell the plip driver to avoid any ports that
appear to be in use by other parallel port devices. Otherwise you can
use plip=parportN where N is a non-zero integer indicating the
parallel port to use. (Using N=0 will disable the plip driver.)
12. Copying, Translations, Closing, etc.
Hey, you made it to the end! (Phew...) Now just the legal stuff.
12.1. Copyright and Disclaimer
This document is Copyright (c) 1995-1999 by Paul Gortmaker. Copying
and redistribution is allowed under the conditions as outlined in the
Linux Documentation Project Copyright, available from where you
obtained this document, OR as outlined in the GNU General Public
License, version 2 (see linux/COPYING).
This document is not gospel. However, it is probably the most up to
date info that you will be able to find. Nobody is responsible for
what happens to your hardware but yourself. If your stuff goes up in
smoke, or anything else bad happens, we take no responsibility. ie.
THE AUTHOR IS NOT RESPONSIBLE FOR ANY DAMAGES INCURRED DUE TO ACTIONS
TAKEN BASED ON THE INFORMATION INCLUDED IN THIS DOCUMENT.
A hint to people considering doing a translation. First, translate
the SGML source (available via FTP from the HowTo main site) so that
you can then generate other output formats. Be sure to keep a copy of
the original English SGML source that you translated from! When an
updated HowTo is released, get the new SGML source for that version,
and then a simple diff -u old.sgml new.sgml will show you exactly what
has changed so that you can easily incorporate those changes into your
translated SMGL source without having to re-read or re-translate
everything.
If you are intending to incorporate this document into a published
work, please make contact (via e-mail) so that you can be supplied
with the most up to date information available. In the past, out of
date versions of the Linux HowTo documents have been published, which
caused the developers undue grief from being plagued with questions
that were already answered in the up to date versions.
12.2. Closing
If you have found any glaring typos, or outdated info in this
document, please let me know. It is easy to overlook stuff, as the
kernel (and the number of drivers) is huge compared to what it was
when I started this.
Thanks,
Paul Gortmaker, p_gortmaker @ yahoo.com
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