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Add comment about max. number of boot options
1 <!-- retain these comments for translator revision tracking -->
2 <!-- $Id$ -->
3
4 <sect1 id="boot-parms"><title>Boot Parameters</title>
5 <para>
6
7 Boot parameters are Linux kernel parameters which are generally used
8 to make sure that peripherals are dealt with properly. For the most
9 part, the kernel can auto-detect information about your peripherals.
10 However, in some cases you'll have to help the kernel a bit.
11
12 </para><para>
13
14 If this is the first time you're booting the system, try the default
15 boot parameters (i.e., don't try setting parameters) and see if it works
16 correctly. It probably will. If not, you can reboot later and look for
17 any special parameters that inform the system about your hardware.
18
19 </para><para>
20
21 Information on many boot parameters can be found in the
22 <ulink url="http://www.tldp.org/HOWTO/BootPrompt-HOWTO.html"> Linux
23 BootPrompt HOWTO</ulink>, including tips for obscure hardware. This
24 section contains only a sketch of the most salient parameters. Some
25 common gotchas are included below in
26 <xref linkend="boot-troubleshooting"/>.
27
28 </para><para>
29
30 When the kernel boots, a message
31
32 <informalexample><screen>
33
34 Memory:<replaceable>avail</replaceable>k/<replaceable>total</replaceable>k available
35
36 </screen></informalexample>
37
38 should be emitted early in the process.
39 <replaceable>total</replaceable> should match the total amount of RAM,
40 in kilobytes. If this doesn't match the actual amount of RAM you have
41 installed, you need to use the
42 <userinput>mem=<replaceable>ram</replaceable></userinput> parameter,
43 where <replaceable>ram</replaceable> is set to the amount of memory,
44 suffixed with ``k'' for kilobytes, or ``m'' for megabytes. For
45 example, both <userinput>mem=65536k</userinput> and
46 <userinput>mem=64m</userinput> mean 64MB of RAM.
47
48 </para><para condition="supports-serial-console">
49
50 If you are booting with a serial console, generally the kernel will
51 autodetect this
52 <phrase arch="mipsel">(although not on DECstations)</phrase>
53 If you have a videocard (framebuffer) and a keyboard also attached to
54 the computer which you wish to boot via serial console, you may have
55 to pass the
56 <userinput>console=<replaceable>device</replaceable></userinput>
57 argument to the kernel, where <replaceable>device</replaceable> is
58 your serial device, which is usually something like
59 <filename>ttyS0</filename>.
60
61 </para><para arch="sparc">
62
63 For &arch-title; the serial devices are <filename>ttya</filename> or
64 <filename>ttyb</filename>.
65 Alternatively, set the <envar>input-device</envar> and
66 <envar>output-device</envar> OpenPROM variables to
67 <filename>ttya</filename>.
68
69 </para>
70
71
72 <sect2 id="installer-args"><title>Debian Installer Parameters</title>
73 <para>
74
75 The installation system recognizes a few additional boot parameters<footnote>
76
77 <para>
78
79 Note that the kernel accepts a maximum of 8 command line options and
80 8 environment options (including any options added by default for the
81 installer). If these numbers are exceeded, 2.4 kernels will drop any
82 excess options and 2.6 kernels will panic.
83
84 </para>
85
86 </footnote> which may be useful.
87
88 </para>
89
90 <variablelist>
91 <varlistentry>
92 <term>debconf/priority</term>
93 <listitem><para>
94
95 This parameter settings will set the highest priority of messages
96 to be displayed.
97
98 </para><para>
99
100 The default installation uses <userinput>debconf/priority=high</userinput>.
101 This means that both high and critical priority messages are shown, but medium
102 and low priority messages are skipped.
103 If problems are encountered, the installer adjusts the priority as needed.
104
105 </para><para>
106
107 If you add <userinput>debconf/priority=medium</userinput> as boot parameter, you
108 will be shown the installation menu and gain more control over the installation.
109 When <userinput>debconf/priority=low</userinput> is used, all messages are shown
110 (this is equivalent to the <emphasis>expert</emphasis> boot method).
111 With <userinput>debconf/priority=critical</userinput>, the installation system
112 will display only critical messages and try to do the right thing without fuss.
113
114 </para></listitem>
115 </varlistentry>
116
117
118 <varlistentry>
119 <term>DEBIAN_FRONTEND</term>
120 <listitem><para>
121
122 This boot parameter controls the type of user interface used for the
123 installer. The current possible parameter settings are:
124
125 <itemizedlist>
126 <listitem>
127 <para><userinput>DEBIAN_FRONTEND=noninteractive</userinput></para>
128 </listitem><listitem>
129 <para><userinput>DEBIAN_FRONTEND=text</userinput></para>
130 </listitem><listitem>
131 <para><userinput>DEBIAN_FRONTEND=newt</userinput></para>
132 </listitem><listitem>
133 <para><userinput>DEBIAN_FRONTEND=slang</userinput></para>
134 </listitem><listitem>
135 <para><userinput>DEBIAN_FRONTEND=ncurses</userinput></para>
136 </listitem><listitem>
137 <para><userinput>DEBIAN_FRONTEND=bogl</userinput></para>
138 </listitem><listitem>
139 <para><userinput>DEBIAN_FRONTEND=gtk</userinput></para>
140 </listitem><listitem>
141 <para><userinput>DEBIAN_FRONTEND=corba</userinput></para>
142 </listitem>
143 </itemizedlist>
144
145 The default front end is <userinput>DEBIAN_FRONTEND=newt</userinput>.
146 <userinput>DEBIAN_FRONTEND=text</userinput> may be preferable for
147 serial console installs. Generally only the
148 <userinput>newt</userinput> frontend is available on default install
149 media, so this is not very useful right now.
150
151 </para></listitem>
152 </varlistentry>
153
154
155 <varlistentry>
156 <term>BOOT_DEBUG</term>
157 <listitem><para>
158
159 Passing this boot parameter will cause the boot to be more verbosely
160 logged.
161
162 <variablelist>
163 <varlistentry>
164 <term><userinput>BOOT_DEBUG=0</userinput></term>
165 <listitem><para>This is the default.</para></listitem>
166 </varlistentry>
167
168 <varlistentry>
169 <term><userinput>BOOT_DEBUG=1</userinput></term>
170 <listitem><para>More verbose than usual.</para></listitem>
171 </varlistentry>
172
173 <varlistentry>
174 <term><userinput>BOOT_DEBUG=2</userinput></term>
175 <listitem><para>Lots of debugging information.</para></listitem>
176 </varlistentry>
177
178 <varlistentry>
179 <term><userinput>BOOT_DEBUG=3</userinput></term>
180 <listitem><para>
181
182 Shells are run at various points in the boot process to allow detailed
183 debugging. Exit the shell to continue the boot.
184
185 </para></listitem>
186 </varlistentry>
187 </variablelist>
188
189 </para></listitem>
190 </varlistentry>
191
192
193 <varlistentry>
194 <term>INSTALL_MEDIA_DEV</term>
195 <listitem><para>
196
197 The value of the parameter is the path to the device to load the
198 Debian installer from. For example,
199 <userinput>INSTALL_MEDIA_DEV=/dev/floppy/0</userinput>
200
201 </para><para>
202
203 The boot floppy, which normally scans all floppies and USB storage
204 devices it can to find the root floppy, can be overridden by this
205 parameter to only look at the one device.
206
207 </para></listitem>
208 </varlistentry>
209
210 <varlistentry>
211 <term>debian-installer/framebuffer</term>
212 <listitem><para>
213
214 Some architectures use the kernel framebuffer to offer installation in
215 a number of languages. If framebuffer causes a problem on your system
216 you can disable the feature by the parameter
217 <userinput>debian-installer/framebuffer=false</userinput>. Problem
218 symptoms are error messages about bterm or bogl, a blank screen, or
219 a freeze within a few minutes after starting the install.
220
221 </para><para arch="i386">
222
223 The <userinput>video=vga16:off</userinput> argument may also be used
224 to disable the framebuffer. Such problems have been reported on a Dell
225 Inspiron with Mobile Radeon card.
226
227 </para><para arch="m68k">
228
229 Such problems have been reported on the Amiga 1200 and SE/30.
230
231 </para><para arch="hppa">
232
233 Such problems have been reported on hppa.
234
235 </para></listitem>
236 </varlistentry>
237
238 <varlistentry>
239 <term>debian-installer/probe/usb</term>
240 <listitem><para>
241
242 Set to <userinput>false</userinput> to prevent probing for USB on
243 boot, if that causes problems.
244
245 </para></listitem>
246 </varlistentry>
247
248 <varlistentry>
249 <term>netcfg/disable_dhcp</term>
250 <listitem><para>
251
252 By default, the &d-i; automatically probes for network configuration
253 via DHCP. If the probe succeeds, you won't have a chance to review and
254 change the obtained settings. You can get to the manual network setup
255 only in case the DHCP probe fails.
256
257 </para><para>
258
259 If you have a DHCP server on your local network, but want to avoid it
260 because e.g. it gives wrong answers, you can use the parameter
261 <userinput>netcfg/disable_dhcp=true</userinput> to prevent configuring
262 the network with DHCP and to enter the information manually.
263
264 </para></listitem>
265 </varlistentry>
266
267 <varlistentry>
268 <term>hw-detect/start_pcmcia</term>
269 <listitem><para>
270
271 Set to <userinput>false</userinput> to prevent starting PCMCIA
272 services, if that causes problems. Some laptops are well known for
273 this misbehavior.
274
275 </para></listitem>
276 </varlistentry>
277
278 <varlistentry>
279 <term>preseed/url</term>
280 <listitem><para>
281
282 Specify the url to a preconfiguration file to download and use in
283 automating the install. See <xref linkend="automatic-install"/>.
284
285 </para></listitem>
286 </varlistentry>
287
288 <varlistentry>
289 <term>preseed/file</term>
290 <listitem><para>
291
292 Specify the url to a preconfiguration file to load to
293 automating the install. See <xref linkend="automatic-install"/>.
294
295 </para></listitem>
296 </varlistentry>
297
298 <varlistentry>
299 <term>ramdisk_size</term>
300 <listitem><para>
301
302 If you are using a 2.2.x kernel, you may need to set &ramdisksize;.
303
304 </para></listitem>
305 </varlistentry>
306
307 </variablelist>
308 </sect2>
309 </sect1>
310

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