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1 | .\" Copyright (c) 1995,1997 Paul Gortmaker and Andries Brouwer |
2 | .\" | |
1dd72f9c | 3 | .\" %%%LICENSE_START(GPLv2+_DOC_FULL) |
fea681da MK |
4 | .\" This is free documentation; you can redistribute it and/or |
5 | .\" modify it under the terms of the GNU General Public License as | |
6 | .\" published by the Free Software Foundation; either version 2 of | |
7 | .\" the License, or (at your option) any later version. | |
8 | .\" | |
9 | .\" The GNU General Public License's references to "object code" | |
10 | .\" and "executables" are to be interpreted as the output of any | |
11 | .\" document formatting or typesetting system, including | |
12 | .\" intermediate and printed output. | |
13 | .\" | |
14 | .\" This manual is distributed in the hope that it will be useful, | |
15 | .\" but WITHOUT ANY WARRANTY; without even the implied warranty of | |
16 | .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
17 | .\" GNU General Public License for more details. | |
18 | .\" | |
19 | .\" You should have received a copy of the GNU General Public | |
c715f741 MK |
20 | .\" License along with this manual; if not, see |
21 | .\" <http://www.gnu.org/licenses/>. | |
6a8d8745 | 22 | .\" %%%LICENSE_END |
fea681da MK |
23 | .\" |
24 | .\" This man page written 950814 by aeb, based on Paul Gortmaker's HOWTO | |
25 | .\" (dated v1.0.1, 15/08/95). | |
26 | .\" Major update, aeb, 970114. | |
27 | .\" | |
ad5b45ab | 28 | .TH BOOTPARAM 7 2014-06-13 "Linux" "Linux Programmer's Manual" |
fea681da | 29 | .SH NAME |
f68512e9 | 30 | bootparam \- introduction to boot time parameters of the Linux kernel |
fea681da | 31 | .SH DESCRIPTION |
76c44d83 | 32 | The Linux kernel accepts certain 'command-line options' or 'boot time |
c13182ef MK |
33 | parameters' at the moment it is started. |
34 | In general this is used to | |
fea681da MK |
35 | supply the kernel with information about hardware parameters that |
36 | the kernel would not be able to determine on its own, or to avoid/override | |
37 | the values that the kernel would otherwise detect. | |
38 | ||
ad8fe082 | 39 | When the kernel is booted directly by the BIOS, |
fea681da MK |
40 | you have no opportunity to specify any parameters. |
41 | So, in order to take advantage of this possibility you have to | |
122a101a | 42 | use a boot loader that is able to pass parameters, such as GRUB. |
fea681da | 43 | |
18299dfc MK |
44 | .\" The LILO program (LInux LOader) written by Werner Almesberger is the |
45 | .\" most commonly used. | |
46 | .\" It has the ability to boot various kernels, and | |
47 | .\" stores the configuration information in a plain text file. | |
48 | .\" (See | |
49 | .\" .BR lilo (8) | |
50 | .\" and | |
51 | .\" .BR lilo.conf (5).) | |
52 | .\" LILO can boot DOS, OS/2, Linux, FreeBSD, UnixWare, etc., and is quite flexible. | |
51700fd7 | 53 | .\" |
18299dfc MK |
54 | .\" The other commonly used Linux loader is 'LoadLin', which is a DOS |
55 | .\" program that has the capability to launch a Linux kernel from the DOS | |
56 | .\" prompt (with boot-args) assuming that certain resources are available. | |
57 | .\" This is good for people that want to launch Linux from DOS. | |
51700fd7 | 58 | .\" |
18299dfc MK |
59 | .\" It is also very useful if you have certain hardware which relies on |
60 | .\" the supplied DOS driver to put the hardware into a known state. | |
61 | .\" A common example is 'SoundBlaster Compatible' sound cards that require | |
62 | .\" the DOS driver to twiddle a few mystical registers to put the card | |
63 | .\" into a SB compatible mode. | |
64 | .\" Booting DOS with the supplied driver, and | |
65 | .\" then loading Linux from the DOS prompt with loadlin avoids the reset | |
66 | .\" of the card that happens if one rebooted instead. | |
73d8cece | 67 | .SS The argument list |
fea681da | 68 | The kernel command line is parsed into a list of strings |
c13182ef | 69 | (boot arguments) separated by spaces. |
36267a51 | 70 | Most of the boot arguments have the form: |
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71 | |
72 | .in +4n | |
73 | .nf | |
fea681da | 74 | name[=value_1][,value_2]...[,value_10] |
77bda21c MK |
75 | .fi |
76 | .in | |
fea681da | 77 | .LP |
40dedbfe | 78 | where 'name' is a unique keyword that is used to identify what part of |
fea681da | 79 | the kernel the associated values (if any) are to be given to. |
33a0ccb2 | 80 | Note the limit of 10 is real, as the present code handles only 10 comma |
c13182ef | 81 | separated parameters per keyword. |
3b777aff | 82 | (However, you can reuse the same |
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83 | keyword with up to an additional 10 parameters in unusually |
84 | complicated situations, assuming the setup function supports it.) | |
85 | ||
e57fca5a MK |
86 | Most of the sorting is coded in the kernel source file |
87 | .IR init/main.c . | |
c13182ef | 88 | First, the kernel |
40dedbfe | 89 | checks to see if the argument is any of the special arguments 'root=', |
25715c96 | 90 | \&'nfsroot=', 'nfsaddrs=', 'ro', 'rw', 'debug' or 'init'. |
c13182ef | 91 | The meaning of these special arguments is described below. |
fea681da | 92 | |
b46a2f4a MK |
93 | Then it walks a list of setup functions |
94 | to see if the specified argument string (such as 'foo') has | |
40dedbfe | 95 | been associated with a setup function ('foo_setup()') for a particular |
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96 | device or part of the kernel. |
97 | If you passed the kernel the line | |
fea681da | 98 | foo=3,4,5,6 then the kernel would search the bootsetups array to see |
40dedbfe | 99 | if 'foo' was registered. |
c13182ef | 100 | If it was, then it would call the setup |
40dedbfe | 101 | function associated with 'foo' (foo_setup()) and hand it the arguments |
31df5734 | 102 | 3, 4, 5, and 6 as given on the kernel command line. |
fea681da | 103 | |
40dedbfe | 104 | Anything of the form 'foo=bar' that is not accepted as a setup function |
fea681da | 105 | as described above is then interpreted as an environment variable to |
c13182ef | 106 | be set. |
40dedbfe | 107 | A (useless?) example would be to use 'TERM=vt100' as a boot |
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108 | argument. |
109 | ||
110 | Any remaining arguments that were not picked up by the kernel and were | |
f184a1c3 MK |
111 | not interpreted as environment variables are then passed onto PID 1, |
112 | which is usually the | |
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113 | .BR init (1) |
114 | program. | |
c13182ef | 115 | The most common argument that |
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116 | is passed to the |
117 | .I init | |
118 | process is the word 'single' which instructs it | |
fea681da | 119 | to boot the computer in single user mode, and not launch all the usual |
c13182ef | 120 | daemons. |
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121 | Check the manual page for the version of |
122 | .BR init (1) | |
123 | installed on | |
fea681da | 124 | your system to see what arguments it accepts. |
76c637e1 | 125 | .SS General non-device-specific boot arguments |
bebbbd1f | 126 | .TP |
40dedbfe | 127 | .B "'init=...'" |
fea681da MK |
128 | This sets the initial command to be executed by the kernel. |
129 | If this is not set, or cannot be found, the kernel will try | |
5ce89119 MK |
130 | .IR /sbin/init , |
131 | then | |
fea681da MK |
132 | .IR /etc/init , |
133 | then | |
134 | .IR /bin/init , | |
135 | then | |
0daa9e92 | 136 | .I /bin/sh |
fea681da | 137 | and panic if all of this fails. |
bebbbd1f | 138 | .TP |
40dedbfe | 139 | .B "'nfsaddrs=...'" |
32ae2e17 | 140 | This sets the NFS boot address to the given string. |
fea681da | 141 | This boot address is used in case of a net boot. |
bebbbd1f | 142 | .TP |
40dedbfe | 143 | .B "'nfsroot=...'" |
5d6aa84a | 144 | This sets the NFS root name to the given string. |
c13182ef | 145 | If this string |
fea681da | 146 | does not begin with '/' or ',' or a digit, then it is prefixed by |
25715c96 | 147 | \&'/tftpboot/'. |
c13182ef | 148 | This root name is used in case of a net boot. |
bebbbd1f | 149 | .TP |
40dedbfe MK |
150 | .B "'no387'" |
151 | (Only when | |
152 | .B CONFIG_BUGi386 | |
153 | is defined.) | |
fea681da | 154 | Some i387 coprocessor chips have bugs that show up when used in 32 bit |
c13182ef MK |
155 | protected mode. |
156 | For example, some of the early ULSI-387 chips would | |
c45bd688 | 157 | cause solid lockups while performing floating-point calculations. |
77bda21c | 158 | Using the 'no387' boot argument causes Linux to ignore the maths |
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159 | coprocessor even if you have one. |
160 | Of course you must then have your | |
fea681da | 161 | kernel compiled with math emulation support! |
bebbbd1f | 162 | .TP |
40dedbfe MK |
163 | .B "'no-hlt'" |
164 | (Only when | |
165 | .B CONFIG_BUGi386 | |
166 | is defined.) | |
167 | Some of the early i486DX-100 chips have a problem with the 'hlt' | |
fea681da | 168 | instruction, in that they can't reliably return to operating mode |
c13182ef | 169 | after this instruction is used. |
40dedbfe | 170 | Using the 'no-hlt' instruction tells |
fea681da | 171 | Linux to just run an infinite loop when there is nothing else to do, |
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172 | and to not halt the CPU. |
173 | This allows people with these broken chips | |
fea681da | 174 | to use Linux. |
bebbbd1f | 175 | .TP |
40dedbfe | 176 | .B "'root=...'" |
fea681da | 177 | This argument tells the kernel what device is to be used as the root |
9ee4a2b6 | 178 | filesystem while booting. |
c13182ef | 179 | The default of this setting is determined |
fea681da | 180 | at compile time, and usually is the value of the root device of the |
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181 | system that the kernel was built on. |
182 | To override this value, and | |
fea681da | 183 | select the second floppy drive as the root device, one would |
6387216b | 184 | use 'root=/dev/fd1'. |
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185 | |
186 | The root device can be specified symbolically or numerically. | |
e57fca5a | 187 | A symbolic specification has the form |
21e79503 | 188 | .IR /dev/XXYN , |
e57fca5a | 189 | where XX designates |
40dedbfe | 190 | the device type ('hd' for ST-506 compatible hard disk, with Y in |
25715c96 MK |
191 | \&'a'-'d'; 'sd' for SCSI compatible disk, with Y in 'a'-'e'; |
192 | \&'ad' for Atari ACSI disk, with Y in 'a'-'e', | |
193 | \&'ez' for a Syquest EZ135 parallel port removable drive, with Y='a', | |
194 | \&'xd' for XT compatible disk, with Y either 'a' or 'b'; 'fd' for | |
5503c85e | 195 | floppy disk, with Y the floppy drive number\(emfd0 would be |
40dedbfe | 196 | the DOS 'A:' drive, and fd1 would be 'B:'), Y the driver letter or |
fea681da | 197 | number, and N the number (in decimal) of the partition on this device |
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198 | (absent in the case of floppies). |
199 | Recent kernels allow many other | |
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200 | types, mostly for CD-ROMs: nfs, ram, scd, mcd, cdu535, aztcd, cm206cd, |
201 | gscd, sbpcd, sonycd, bpcd. | |
202 | (The type nfs specifies a net boot; ram refers to a ram disk.) | |
203 | ||
204 | Note that this has nothing to do with the designation of these | |
9ee4a2b6 | 205 | devices on your filesystem. |
40dedbfe | 206 | The '/dev/' part is purely conventional. |
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207 | |
208 | The more awkward and less portable numeric specification of the above | |
c13182ef | 209 | possible root devices in major/minor format is also accepted. |
59dc509c | 210 | (For example, |
e57fca5a MK |
211 | .I /dev/sda3 |
212 | is major 8, minor 3, so you could use 'root=0x803' as an | |
fea681da | 213 | alternative.) |
bebbbd1f | 214 | .TP |
1c137827 | 215 | .BR "'rootdelay='" |
91085d85 | 216 | This parameter sets the delay (in seconds) to pause before attempting |
1c137827 PG |
217 | to mount the root filesystem. |
218 | .TP | |
219 | .BR "'rootflags=...'" | |
ffe8d0b1 MK |
220 | This parameter sets the mount option string for the root filesystem |
221 | (see also | |
1c137827 PG |
222 | .BR fstab (5)). |
223 | .TP | |
6c8adf48 JLDL |
224 | .BR "'rootfstype=...'" |
225 | The 'rootfstype' option tells the kernel to mount the root filesystem as | |
226 | if it where of the type specified. | |
227 | This can be useful (for example) to | |
228 | mount an ext3 filesystem as ext2 and then remove the journal in the root | |
229 | filesystem, in fact reverting its format from ext3 to ext2 without the | |
230 | need to boot the box from alternate media. | |
231 | .TP | |
40dedbfe | 232 | .BR 'ro' " and " 'rw' |
9ee4a2b6 MK |
233 | The 'ro' option tells the kernel to mount the root filesystem |
234 | as 'read-only' so that filesystem consistency check programs (fsck) | |
235 | can do their work on a quiescent filesystem. | |
c13182ef | 236 | No processes can |
9ee4a2b6 | 237 | write to files on the filesystem in question until it is 'remounted' |
40dedbfe | 238 | as read/write capable, for example, by 'mount \-w \-n \-o remount /'. |
fea681da MK |
239 | (See also |
240 | .BR mount (8).) | |
241 | ||
9ee4a2b6 | 242 | The 'rw' option tells the kernel to mount the root filesystem read/write. |
fea681da MK |
243 | This is the default. |
244 | ||
bebbbd1f | 245 | .TP |
d11f367d AR |
246 | .B "'resume=...'" |
247 | This tells the kernel the location of the suspend-to-disk data that you want the machine to resume from after hibernation. | |
063692c0 MK |
248 | Usually, it is the same as your swap partition or file. |
249 | Example: | |
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250 | |
251 | .in +4n | |
252 | .nf | |
253 | resume=/dev/hda2 | |
254 | .fi | |
255 | .in | |
d11f367d | 256 | .TP |
40dedbfe | 257 | .B "'reserve=...'" |
c13182ef MK |
258 | This is used to protect I/O port regions from probes. |
259 | The form of the command is: | |
77bda21c MK |
260 | |
261 | .in +4n | |
262 | .nf | |
fea681da | 263 | .BI reserve= iobase,extent[,iobase,extent]... |
77bda21c MK |
264 | .fi |
265 | .in | |
bebbbd1f | 266 | .sp |
fea681da | 267 | In some machines it may be necessary to prevent device drivers from |
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268 | checking for devices (auto-probing) in a specific region. |
269 | This may be | |
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270 | because of hardware that reacts badly to the probing, or hardware |
271 | that would be mistakenly identified, or merely | |
272 | hardware you don't want the kernel to initialize. | |
273 | ||
274 | The reserve boot-time argument specifies an I/O port region that | |
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275 | shouldn't be probed. |
276 | A device driver will not probe a reserved region, | |
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277 | unless another boot argument explicitly specifies that it do so. |
278 | ||
279 | For example, the boot line | |
77bda21c MK |
280 | |
281 | .in +4n | |
282 | .nf | |
fea681da | 283 | reserve=0x300,32 blah=0x300 |
77bda21c MK |
284 | .fi |
285 | .in | |
bebbbd1f | 286 | .IP |
40dedbfe | 287 | keeps all device drivers except the driver for 'blah' from probing |
94e9d9fe | 288 | 0x300\-0x31f. |
bebbbd1f | 289 | .TP |
40dedbfe | 290 | .B "'mem=...'" |
fea681da | 291 | The BIOS call defined in the PC specification that returns |
33a0ccb2 | 292 | the amount of installed memory was designed only to be able |
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293 | to report up to 64MB. |
294 | Linux uses this BIOS call at boot to | |
295 | determine how much memory is installed. | |
296 | If you have more than 64MB of | |
77bda21c | 297 | RAM installed, you can use this boot argument to tell Linux how much memory |
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298 | you have. |
299 | The value is in decimal or hexadecimal (prefix 0x), | |
40dedbfe MK |
300 | and the suffixes 'k' (times 1024) or 'M' (times 1048576) can be used. |
301 | Here is a quote from Linus on usage of the 'mem=' parameter. | |
fea681da | 302 | |
324633ae | 303 | .in +0.5i |
40dedbfe | 304 | The kernel will accept any 'mem=xx' parameter you give it, and if it |
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305 | turns out that you lied to it, it will crash horribly sooner or later. |
306 | The parameter indicates the highest addressable RAM address, so | |
40dedbfe MK |
307 | \&'mem=0x1000000' means you have 16MB of memory, for example. |
308 | For a 96MB machine this would be 'mem=0x6000000'. | |
fea681da | 309 | |
192e4f2e MK |
310 | .BR NOTE : |
311 | some machines might use the top of memory for BIOS | |
4f9d18f8 | 312 | caching or whatever, so you might not actually have up to the full |
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313 | 96MB addressable. |
314 | The reverse is also true: some chipsets will map | |
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315 | the physical memory that is covered by the BIOS area into the area |
316 | just past the top of memory, so the top-of-mem might actually be 96MB | |
c13182ef MK |
317 | + 384kB for example. |
318 | If you tell linux that it has more memory than | |
fea681da | 319 | it actually does have, bad things will happen: maybe not at once, but |
324633ae MK |
320 | surely eventually. |
321 | .in | |
fea681da | 322 | |
40dedbfe | 323 | You can also use the boot argument 'mem=nopentium' to turn off 4 MB |
eb1af896 | 324 | page tables on kernels configured for IA32 systems with a pentium or newer |
441082ad | 325 | CPU. |
bebbbd1f | 326 | .TP |
40dedbfe | 327 | .B "'panic=N'" |
b9aee8fe | 328 | By default, the kernel will not reboot after a panic, but this option |
f7ceac86 | 329 | will cause a kernel reboot after N seconds (if N is greater than zero). |
77bda21c MK |
330 | This panic timeout can also be set by |
331 | ||
332 | .in +4n | |
333 | .nf | |
1322e836 | 334 | echo N > /proc/sys/kernel/panic |
77bda21c MK |
335 | .fi |
336 | .in | |
bebbbd1f | 337 | .TP |
40dedbfe MK |
338 | .B "'reboot=[warm|cold][,[bios|hard]]'" |
339 | (Only when | |
340 | .B CONFIG_BUGi386 | |
341 | is defined.) | |
fea681da | 342 | Since 2.0.22 a reboot is by default a cold reboot. |
40dedbfe | 343 | One asks for the old default with 'reboot=warm'. |
fea681da MK |
344 | (A cold reboot may be required to reset certain hardware, |
345 | but might destroy not yet written data in a disk cache. | |
346 | A warm reboot may be faster.) | |
b9aee8fe | 347 | By default, a reboot is hard, by asking the keyboard controller |
fea681da | 348 | to pulse the reset line low, but there is at least one type |
c13182ef | 349 | of motherboard where that doesn't work. |
40dedbfe | 350 | The option 'reboot=bios' will |
fea681da | 351 | instead jump through the BIOS. |
bebbbd1f | 352 | .TP |
40dedbfe | 353 | .BR 'nosmp' " and " 'maxcpus=N' |
fea681da | 354 | (Only when __SMP__ is defined.) |
40dedbfe MK |
355 | A command-line option of 'nosmp' or 'maxcpus=0' will disable SMP |
356 | activation entirely; an option 'maxcpus=N' limits the maximum number | |
fea681da | 357 | of CPUs activated in SMP mode to N. |
73d8cece | 358 | .SS Boot arguments for use by kernel developers |
bebbbd1f | 359 | .TP |
40dedbfe | 360 | .B "'debug'" |
fea681da | 361 | Kernel messages are handed off to the kernel log daemon klogd so that they |
c13182ef MK |
362 | may be logged to disk. |
363 | Messages with a priority above | |
fea681da | 364 | .I console_loglevel |
c13182ef | 365 | are also printed on the console. |
e57fca5a MK |
366 | (For these levels, see |
367 | .IR <linux/kernel.h> .) | |
b9aee8fe | 368 | By default, this variable is set to log anything more important than |
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369 | debug messages. |
370 | This boot argument will cause the kernel to also | |
fea681da MK |
371 | print the messages of DEBUG priority. |
372 | The console loglevel can also be set at run time via an option | |
c13182ef MK |
373 | to klogd. |
374 | See | |
fea681da | 375 | .BR klogd (8). |
bebbbd1f | 376 | .TP |
40dedbfe | 377 | .B "'profile=N'" |
fea681da MK |
378 | It is possible to enable a kernel profiling function, |
379 | if one wishes to find out where the kernel is spending its CPU cycles. | |
380 | Profiling is enabled by setting the variable | |
381 | .I prof_shift | |
c7094399 | 382 | to a nonzero value. |
40dedbfe MK |
383 | This is done either by specifying |
384 | .B CONFIG_PROFILE | |
385 | at compile time, or by giving the 'profile=' option. | |
fea681da MK |
386 | Now the value that |
387 | .I prof_shift | |
40dedbfe MK |
388 | gets will be N, when given, or |
389 | .BR CONFIG_PROFILE_SHIFT , | |
390 | when that is given, or 2, the default. | |
c13182ef | 391 | The significance of this variable is that it |
fea681da MK |
392 | gives the granularity of the profiling: each clock tick, if the |
393 | system was executing kernel code, a counter is incremented: | |
77bda21c MK |
394 | |
395 | .in +4n | |
396 | .nf | |
fea681da | 397 | profile[address >> prof_shift]++; |
77bda21c MK |
398 | .fi |
399 | .in | |
bebbbd1f | 400 | .sp |
fea681da MK |
401 | The raw profiling information can be read from |
402 | .IR /proc/profile . | |
403 | Probably you'll want to use a tool such as readprofile.c to digest it. | |
404 | Writing to | |
405 | .I /proc/profile | |
406 | will clear the counters. | |
bebbbd1f | 407 | .TP |
40dedbfe | 408 | .B "'swap=N1,N2,N3,N4,N5,N6,N7,N8'" |
fea681da MK |
409 | Set the eight parameters max_page_age, page_advance, page_decline, |
410 | page_initial_age, age_cluster_fract, age_cluster_min, pageout_weight, | |
411 | bufferout_weight that control the kernel swap algorithm. | |
412 | For kernel tuners only. | |
bebbbd1f | 413 | .TP |
40dedbfe | 414 | .B "'buff=N1,N2,N3,N4,N5,N6'" |
fea681da MK |
415 | Set the six parameters max_buff_age, buff_advance, buff_decline, |
416 | buff_initial_age, bufferout_weight, buffermem_grace that control | |
c13182ef MK |
417 | kernel buffer memory management. |
418 | For kernel tuners only. | |
73d8cece | 419 | .SS Boot arguments for ramdisk use |
40dedbfe MK |
420 | (Only if the kernel was compiled with |
421 | .BR CONFIG_BLK_DEV_RAM .) | |
5503c85e MK |
422 | In general it is a bad idea to use a ramdisk under Linux\(emthe |
423 | system will use available memory more efficiently itself. | |
fea681da MK |
424 | But while booting (or while constructing boot floppies) |
425 | it is often useful to load the floppy contents into a | |
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426 | ramdisk. |
427 | One might also have a system in which first | |
9ee4a2b6 | 428 | some modules (for filesystem or hardware) must be loaded |
fea681da MK |
429 | before the main disk can be accessed. |
430 | ||
431 | In Linux 1.3.48, ramdisk handling was changed drastically. | |
432 | Earlier, the memory was allocated statically, and there was | |
40dedbfe | 433 | a 'ramdisk=N' parameter to tell its size. |
421405f9 | 434 | (This could also be set in the kernel image at compile time.) |
fea681da | 435 | These days ram disks use the buffer cache, and grow dynamically. |
421405f9 | 436 | For a lot of information in conjunction with the new ramdisk |
22367af2 | 437 | setup, see the kernel source file |
51700fd7 | 438 | .IR Documentation/blockdev/ramdisk.txt |
e57fca5a MK |
439 | .RI ( Documentation/ramdisk.txt |
440 | in older kernels). | |
fea681da MK |
441 | |
442 | There are four parameters, two boolean and two integral. | |
bebbbd1f | 443 | .TP |
40dedbfe | 444 | .B "'load_ramdisk=N'" |
c13182ef MK |
445 | If N=1, do load a ramdisk. |
446 | If N=0, do not load a ramdisk. | |
fea681da | 447 | (This is the default.) |
bebbbd1f | 448 | .TP |
40dedbfe | 449 | .B "'prompt_ramdisk=N'" |
c13182ef MK |
450 | If N=1, do prompt for insertion of the floppy. |
451 | (This is the default.) | |
452 | If N=0, do not prompt. | |
453 | (Thus, this parameter is never needed.) | |
bebbbd1f | 454 | .TP |
40dedbfe | 455 | .BR 'ramdisk_size=N' " or (obsolete) " 'ramdisk=N' |
c13182ef MK |
456 | Set the maximal size of the ramdisk(s) to N kB. |
457 | The default is 4096 (4 MB). | |
bebbbd1f | 458 | .TP |
40dedbfe | 459 | .B "'ramdisk_start=N'" |
fea681da MK |
460 | Sets the starting block number (the offset on the floppy where |
461 | the ramdisk starts) to N. | |
462 | This is needed in case the ramdisk follows a kernel image. | |
bebbbd1f | 463 | .TP |
40dedbfe MK |
464 | .B "'noinitrd'" |
465 | (Only if the kernel was compiled with | |
466 | .B CONFIG_BLK_DEV_RAM | |
467 | and | |
468 | .BR CONFIG_BLK_DEV_INITRD .) | |
fea681da MK |
469 | These days it is possible to compile the kernel to use initrd. |
470 | When this feature is enabled, the boot process will load the kernel | |
471 | and an initial ramdisk; then the kernel converts initrd into | |
472 | a "normal" ramdisk, which is mounted read-write as root device; | |
e57fca5a MK |
473 | then |
474 | .I /linuxrc | |
9ee4a2b6 MK |
475 | is executed; afterward the "real" root filesystem is mounted, |
476 | and the initrd filesystem is moved over to | |
e57fca5a MK |
477 | .IR /initrd ; |
478 | finally | |
479 | the usual boot sequence (e.g., invocation of | |
480 | .IR /sbin/init ) | |
481 | is performed. | |
fea681da | 482 | |
e57fca5a MK |
483 | For a detailed description of the initrd feature, see the kernel source file |
484 | .IR Documentation/initrd.txt . | |
fea681da | 485 | |
40dedbfe | 486 | The 'noinitrd' option tells the kernel that although it was compiled for |
fea681da MK |
487 | operation with initrd, it should not go through the above steps, but |
488 | leave the initrd data under | |
489 | .IR /dev/initrd . | |
4d9b6984 | 490 | (This device can be used only once: the data is freed as soon as |
fea681da MK |
491 | the last process that used it has closed |
492 | .IR /dev/initrd .) | |
73d8cece | 493 | .SS Boot arguments for SCSI devices |
fea681da MK |
494 | General notation for this section: |
495 | ||
496 | .I iobase | |
c13182ef MK |
497 | -- the first I/O port that the SCSI host occupies. |
498 | These are specified in hexadecimal notation, | |
499 | and usually lie in the range from 0x200 to 0x3ff. | |
fea681da MK |
500 | |
501 | .I irq | |
502 | -- the hardware interrupt that the card is configured to use. | |
503 | Valid values will be dependent on the card in question, but will | |
c13182ef MK |
504 | usually be 5, 7, 9, 10, 11, 12, and 15. |
505 | The other values are usually | |
fea681da | 506 | used for common peripherals like IDE hard disks, floppies, serial |
fb3969cd | 507 | ports, and so on. |
fea681da MK |
508 | |
509 | .I scsi-id | |
510 | -- the ID that the host adapter uses to identify itself on the | |
c13182ef MK |
511 | SCSI bus. |
512 | Only some host adapters allow you to change this value, as | |
513 | most have it permanently specified internally. | |
514 | The usual default value | |
fea681da MK |
515 | is 7, but the Seagate and Future Domain TMC-950 boards use 6. |
516 | ||
517 | .I parity | |
518 | -- whether the SCSI host adapter expects the attached devices | |
c13182ef MK |
519 | to supply a parity value with all information exchanges. |
520 | Specifying a one indicates parity checking is enabled, | |
521 | and a zero disables parity checking. | |
522 | Again, not all adapters will support selection of parity | |
d9bfdb9c | 523 | behavior as a boot argument. |
bebbbd1f | 524 | .TP |
40dedbfe | 525 | .B "'max_scsi_luns=...'" |
310672d6 | 526 | A SCSI device can have a number of 'subdevices' contained within |
c13182ef MK |
527 | itself. |
528 | The most common example is one of the new SCSI CD-ROMs that | |
529 | handle more than one disk at a time. | |
530 | Each CD is addressed as a | |
25715c96 | 531 | \&'Logical Unit Number' (LUN) of that particular device. |
c13182ef | 532 | But most |
fea681da MK |
533 | devices, such as hard disks, tape drives and such are only one device, |
534 | and will be assigned to LUN zero. | |
535 | ||
536 | Some poorly designed SCSI devices cannot handle being probed for | |
c13182ef | 537 | LUNs not equal to zero. |
29aceda4 | 538 | Therefore, if the compile-time flag |
40dedbfe | 539 | .B CONFIG_SCSI_MULTI_LUN |
e0a06014 | 540 | is not set, newer kernels will by default probe only LUN zero. |
fea681da MK |
541 | |
542 | To specify the number of probed LUNs at boot, one enters | |
25715c96 | 543 | \&'max_scsi_luns=n' as a boot arg, where n is a number between one and |
c13182ef MK |
544 | eight. |
545 | To avoid problems as described above, one would use n=1 to | |
fea681da | 546 | avoid upsetting such broken devices. |
bebbbd1f MK |
547 | .TP |
548 | .B "SCSI tape configuration" | |
fea681da MK |
549 | Some boot time configuration of the SCSI tape driver can be achieved |
550 | by using the following: | |
77bda21c MK |
551 | |
552 | .in +4n | |
553 | .nf | |
fea681da | 554 | .BI st= buf_size[,write_threshold[,max_bufs]] |
77bda21c MK |
555 | .fi |
556 | .in | |
bebbbd1f | 557 | .sp |
c13182ef MK |
558 | The first two numbers are specified in units of kB. |
559 | The default | |
fea681da MK |
560 | .I buf_size |
561 | is 32kB, and the maximum size that can be specified is a | |
c13182ef MK |
562 | ridiculous 16384kB. |
563 | The | |
fea681da MK |
564 | .I write_threshold |
565 | is the value at which the buffer is committed to tape, with a | |
c13182ef MK |
566 | default value of 30kB. |
567 | The maximum number of buffers varies | |
fea681da MK |
568 | with the number of drives detected, and has a default of two. |
569 | An example usage would be: | |
77bda21c MK |
570 | |
571 | .in +4n | |
572 | .nf | |
fea681da | 573 | st=32,30,2 |
77bda21c MK |
574 | .fi |
575 | .in | |
bebbbd1f | 576 | .IP |
4568d084 MK |
577 | Full details can be found in the file |
578 | .I Documentation/scsi/st.txt | |
579 | (or | |
580 | .I drivers/scsi/README.st | |
66a9882e | 581 | for older kernels) in the Linux kernel source. |
73d8cece | 582 | .SS Hard disks |
bebbbd1f MK |
583 | .TP |
584 | .B "IDE Disk/CD-ROM Driver Parameters" | |
fea681da | 585 | The IDE driver accepts a number of parameters, which range from disk |
c13182ef | 586 | geometry specifications, to support for broken controller chips. |
e2badfdf | 587 | Drive-specific options are specified by using 'hdX=' with X in 'a'-'h'. |
fea681da | 588 | |
e2badfdf MK |
589 | Non-drive-specific options are specified with the prefix 'hd='. |
590 | Note that using a drive-specific prefix for a non-drive-specific option | |
fea681da MK |
591 | will still work, and the option will just be applied as expected. |
592 | ||
40dedbfe | 593 | Also note that 'hd=' can be used to refer to the next unspecified |
c13182ef MK |
594 | drive in the (a, ..., h) sequence. |
595 | For the following discussions, | |
40dedbfe | 596 | the 'hd=' option will be cited for brevity. |
c13182ef | 597 | See the file |
0eb9025a | 598 | .I Documentation/ide/ide.txt |
4568d084 | 599 | (or |
0eb9025a MK |
600 | .I Documentation/ide.txt |
601 | .\" Linux 2.0, 2.2, 2.4 | |
602 | in older kernels, or | |
4568d084 | 603 | .I drivers/block/README.ide |
0eb9025a | 604 | in ancient kernels) in the Linux kernel source for more details. |
bebbbd1f | 605 | .TP |
40dedbfe | 606 | .B "The 'hd=cyls,heads,sects[,wpcom[,irq]]' options" |
fea681da | 607 | These options are used to specify the physical geometry of the disk. |
c13182ef MK |
608 | Only the first three values are required. |
609 | The cylinder/head/sectors | |
610 | values will be those used by fdisk. | |
611 | The write precompensation value | |
612 | is ignored for IDE disks. | |
613 | The IRQ value specified will be the IRQ | |
fea681da | 614 | used for the interface that the drive resides on, and is not really a |
e2badfdf | 615 | drive-specific parameter. |
bebbbd1f | 616 | .TP |
40dedbfe | 617 | .B "The 'hd=serialize' option" |
fea681da MK |
618 | The dual IDE interface CMD-640 chip is broken as designed such that |
619 | when drives on the secondary interface are used at the same time as | |
c13182ef MK |
620 | drives on the primary interface, it will corrupt your data. |
621 | Using this | |
fea681da MK |
622 | option tells the driver to make sure that both interfaces are never |
623 | used at the same time. | |
bebbbd1f | 624 | .TP |
40dedbfe | 625 | .B "The 'hd=dtc2278' option" |
fea681da | 626 | This option tells the driver that you have a DTC-2278D IDE interface. |
e2badfdf | 627 | The driver then tries to do DTC-specific operations to enable the |
fea681da | 628 | second interface and to enable faster transfer modes. |
bebbbd1f | 629 | .TP |
40dedbfe | 630 | .B "The 'hd=noprobe' option" |
c13182ef MK |
631 | Do not probe for this drive. |
632 | For example, | |
77bda21c MK |
633 | |
634 | .in +4n | |
635 | .nf | |
fea681da | 636 | hdb=noprobe hdb=1166,7,17 |
77bda21c MK |
637 | .fi |
638 | .in | |
bebbbd1f | 639 | .IP |
fea681da MK |
640 | would disable the probe, but still specify the drive geometry so |
641 | that it would be registered as a valid block device, and hence | |
642 | usable. | |
bebbbd1f | 643 | .TP |
40dedbfe MK |
644 | .B "The 'hd=nowerr' option" |
645 | Some drives apparently have the | |
646 | .B WRERR_STAT | |
647 | bit stuck on permanently. | |
fea681da | 648 | This enables a work-around for these broken devices. |
bebbbd1f | 649 | .TP |
40dedbfe | 650 | .B "The 'hd=cdrom' option" |
fea681da | 651 | This tells the IDE driver that there is an ATAPI compatible CD-ROM |
c13182ef MK |
652 | attached in place of a normal IDE hard disk. |
653 | In most cases the CD-ROM | |
fea681da | 654 | is identified automatically, but if it isn't then this may help. |
bebbbd1f | 655 | .TP |
40dedbfe | 656 | .B "Standard ST-506 Disk Driver Options ('hd=')" |
fea681da | 657 | The standard disk driver can accept geometry arguments for the disks |
c13182ef | 658 | similar to the IDE driver. |
33a0ccb2 | 659 | Note however that it expects only three |
c13182ef | 660 | values (C/H/S); any more or any less and it will silently ignore you. |
33a0ccb2 | 661 | Also, it accepts only 'hd=' as an argument, that is, 'hda=' |
c13182ef MK |
662 | and so on are not valid here. |
663 | The format is as follows: | |
77bda21c MK |
664 | |
665 | .in +4n | |
666 | .nf | |
fea681da | 667 | hd=cyls,heads,sects |
77bda21c MK |
668 | .fi |
669 | .in | |
bebbbd1f | 670 | .IP |
fea681da MK |
671 | If there are two disks installed, the above is repeated with the |
672 | geometry parameters of the second disk. | |
bebbbd1f | 673 | .TP |
40dedbfe | 674 | .B "XT Disk Driver Options ('xd=')" |
1be0d829 MK |
675 | If you are unfortunate enough to be using one of these old 8-bit cards |
676 | that move data at a whopping 125kB/s, then here is the scoop. | |
77bda21c MK |
677 | If the card is not recognized, |
678 | you will have to use a boot argument of the form: | |
679 | ||
680 | .in +4n | |
681 | .nf | |
fea681da | 682 | xd=type,irq,iobase,dma_chan |
77bda21c MK |
683 | .fi |
684 | .in | |
bebbbd1f | 685 | .IP |
fea681da | 686 | The type value specifies the particular manufacturer of the card, |
c13182ef MK |
687 | overriding autodetection. |
688 | For the types to use, consult the | |
fea681da | 689 | .I drivers/block/xd.c |
c13182ef MK |
690 | source file of the kernel you are using. |
691 | The type is an index in the list | |
fea681da MK |
692 | .I xd_sigs |
693 | and in the course of time | |
694 | .\" 1.1.50, 1.3.81, 1.3.99, 2.0.34, 2.1.67, 2.1.78, 2.1.127 | |
695 | types have been added to or deleted from the middle of the list, | |
c13182ef MK |
696 | changing all type numbers. |
697 | Today (Linux 2.5.0) the types are | |
fea681da MK |
698 | 0=generic; 1=DTC 5150cx; 2,3=DTC 5150x; 4,5=Western Digital; |
699 | 6,7,8=Seagate; 9=Omti; 10=XEBEC, and where here several types are | |
700 | given with the same designation, they are equivalent. | |
701 | ||
702 | The xd_setup() function does no checking on the values, and assumes | |
c13182ef MK |
703 | that you entered all four values. |
704 | Don't disappoint it. | |
705 | Here is an | |
fea681da | 706 | example usage for a WD1002 controller with the BIOS disabled/removed, |
40dedbfe | 707 | using the 'default' XT controller parameters: |
77bda21c MK |
708 | |
709 | .in +4n | |
710 | .nf | |
fea681da | 711 | xd=2,5,0x320,3 |
77bda21c MK |
712 | .fi |
713 | .in | |
bebbbd1f MK |
714 | .TP |
715 | .B "Syquest's EZ* removable disks" | |
77bda21c MK |
716 | Syntax: |
717 | ||
718 | .in +4n | |
719 | .nf | |
fea681da | 720 | .BI ez= iobase[,irq[,rep[,nybble]]] |
77bda21c MK |
721 | .fi |
722 | .in | |
73d8cece | 723 | .SS Ethernet devices |
fea681da | 724 | Different drivers make use of different parameters, but they all at |
c13182ef MK |
725 | least share having an IRQ, an I/O port base value, and a name. |
726 | In its most generic form, it looks something like this: | |
77bda21c MK |
727 | |
728 | .in +4n | |
729 | .nf | |
fea681da | 730 | ether=irq,iobase[,param_1[,...param_8]],name |
77bda21c MK |
731 | .fi |
732 | .in | |
733 | ||
80c9146c | 734 | The first nonnumeric argument is taken as the name. |
c13182ef MK |
735 | The param_n values (if applicable) usually have different meanings for each |
736 | different card/driver. | |
737 | Typical param_n values are used to specify | |
fea681da MK |
738 | things like shared memory address, interface selection, DMA channel |
739 | and the like. | |
740 | ||
741 | The most common use of this parameter is to force probing for a second | |
33a0ccb2 | 742 | ethercard, as the default is to probe only for one. |
c13182ef | 743 | This can be accomplished with a simple: |
77bda21c MK |
744 | |
745 | .in +4n | |
746 | .nf | |
fea681da | 747 | ether=0,0,eth1 |
77bda21c MK |
748 | .fi |
749 | .in | |
750 | ||
fea681da MK |
751 | Note that the values of zero for the IRQ and I/O base in the above |
752 | example tell the driver(s) to autoprobe. | |
753 | ||
754 | The Ethernet-HowTo has extensive documentation on using multiple | |
e2badfdf | 755 | cards and on the card/driver-specific implementation |
c13182ef MK |
756 | of the param_n values where used. |
757 | Interested readers should refer to | |
fea681da | 758 | the section in that document on their particular card. |
73d8cece | 759 | .SS The floppy disk driver |
fea681da | 760 | There are many floppy driver options, and they are all listed in |
cb6cb860 | 761 | .I Documentation/blockdev/floppy.txt |
4568d084 | 762 | (or |
cb6cb860 MK |
763 | .I Documentation/floppy.txt |
764 | in oplder kernels, or | |
4568d084 | 765 | .I drivers/block/README.fd |
cb6cb860 | 766 | for ancient kernels) in the Linux kernel source. |
3dd80946 | 767 | See that file for the details. |
73d8cece | 768 | .SS The sound driver |
92b451e5 | 769 | The sound driver can also accept boot arguments to override the compiled-in |
c13182ef MK |
770 | values. |
771 | This is not recommended, as it is rather complex. | |
66a9882e | 772 | It is described in the Linux kernel source file |
ef505ff0 MK |
773 | .IR Documentation/sound/oss/README.OSS |
774 | .RI ( drivers/sound/Readme.linux | |
775 | in older kernel versions). | |
c13182ef | 776 | It accepts |
77bda21c MK |
777 | a boot argument of the form: |
778 | ||
779 | .in +4n | |
780 | .nf | |
fea681da | 781 | sound=device1[,device2[,device3...[,device10]]] |
77bda21c MK |
782 | .fi |
783 | .in | |
bebbbd1f | 784 | .IP |
fea681da MK |
785 | where each deviceN value is of the following format 0xTaaaId and the |
786 | bytes are used as follows: | |
787 | ||
4d9b6984 | 788 | T \- device type: 1=FM, 2=SB, 3=PAS, 4=GUS, 5=MPU401, 6=SB16, |
fea681da MK |
789 | 7=SB16-MPU401 |
790 | ||
4d9b6984 | 791 | aaa \- I/O address in hex. |
fea681da | 792 | |
4d9b6984 | 793 | I \- interrupt line in hex (i.e 10=a, 11=b, ...) |
fea681da | 794 | |
4d9b6984 | 795 | d \- DMA channel. |
fea681da | 796 | |
92b451e5 | 797 | As you can see, it gets pretty messy, and you are better off to compile |
c13182ef | 798 | in your own personal values as recommended. |
77bda21c | 799 | Using a boot argument of |
25715c96 | 800 | \&'sound=0' will disable the sound driver entirely. |
73d8cece | 801 | .SS The line printer driver |
bebbbd1f | 802 | .TP |
40dedbfe | 803 | .B "'lp='" |
77bda21c | 804 | .br |
fea681da | 805 | Syntax: |
77bda21c MK |
806 | |
807 | .in +4n | |
808 | .nf | |
fea681da | 809 | lp=0 |
fea681da | 810 | lp=auto |
fea681da | 811 | lp=reset |
fea681da | 812 | lp=port[,port...] |
77bda21c MK |
813 | .fi |
814 | .in | |
bebbbd1f | 815 | .IP |
fea681da | 816 | You can tell the printer driver what ports to use and what ports not |
c13182ef MK |
817 | to use. |
818 | The latter comes in handy if you don't want the printer driver | |
fea681da | 819 | to claim all available parallel ports, so that other drivers |
75b94dc3 | 820 | (e.g., PLIP, PPA) can use them instead. |
fea681da | 821 | |
c13182ef MK |
822 | The format of the argument is multiple port names. |
823 | For example, | |
fea681da | 824 | lp=none,parport0 would use the first parallel port for lp1, and |
c13182ef MK |
825 | disable lp0. |
826 | To disable the printer driver entirely, one can use | |
fea681da | 827 | lp=0. |
fd7f0a7f MK |
828 | .\" .SH AUTHORS |
829 | .\" Linus Torvalds (and many others) | |
47297adb | 830 | .SH SEE ALSO |
fea681da | 831 | .BR klogd (8), |
421405f9 | 832 | .BR mount (8) |
fea681da MK |
833 | |
834 | Large parts of this man page have been derived from the | |
835 | Boot Parameter HOWTO (version 1.0.1) written by Paul Gortmaker. | |
836 | More information may be found in this (or a more recent) HOWTO. | |
e57fca5a MK |
837 | An up-to-date source of information is the kernel source file |
838 | .IR Documentation/kernel-parameters.txt . |