~qbalazs/installation-guide/lp1030336

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<!-- $Id: parameters.xml 30084 2005-08-20 19:18:11Z fjp $ -->

 <sect1 id="boot-parms"><title>Boot Parameters</title>
<para>

Boot parameters are Linux kernel parameters which are generally used
to make sure that peripherals are dealt with properly.  For the most
part, the kernel can auto-detect information about your peripherals.
However, in some cases you'll have to help the kernel a bit.

</para><para>

If this is the first time you're booting the system, try the default
boot parameters (i.e., don't try setting parameters) and see if it works
correctly. It probably will.  If not, you can reboot later and look for
any special parameters that inform the system about your hardware.

</para><para>

Information on many boot parameters can be found in the
<ulink url="http://www.tldp.org/HOWTO/BootPrompt-HOWTO.html"> Linux
BootPrompt HOWTO</ulink>, including tips for obscure hardware.  This
section contains only a sketch of the most salient parameters.  Some
common gotchas are included below in
<xref linkend="boot-troubleshooting"/>.

</para><para>

When the kernel boots, a message

<informalexample><screen>
Memory:<replaceable>avail</replaceable>k/<replaceable>total</replaceable>k available
</screen></informalexample>

should be emitted early in the process.
<replaceable>total</replaceable> should match the total amount of RAM,
in kilobytes.  If this doesn't match the actual amount of RAM you have
installed, you need to use the
<userinput>mem=<replaceable>ram</replaceable></userinput> parameter,
where <replaceable>ram</replaceable> is set to the amount of memory,
suffixed with <quote>k</quote> for kilobytes, or <quote>m</quote> for
megabytes.  For example, both <userinput>mem=65536k</userinput> and
<userinput>mem=64m</userinput> mean 64MB of RAM.

</para><para condition="supports-serial-console">

If you are booting with a serial console, generally the kernel will
autodetect
this<phrase arch="mipsel"> (although not on DECstations)</phrase>.
If you have a videocard (framebuffer) and a keyboard also attached to
the computer which you wish to boot via serial console, you may have
to pass the
<userinput>console=<replaceable>device</replaceable></userinput>
argument to the kernel, where <replaceable>device</replaceable> is
your serial device, which is usually something like
<filename>ttyS0</filename>.

</para><para arch="sparc">

For &arch-title; the serial devices are <filename>ttya</filename> or
<filename>ttyb</filename>.
Alternatively, set the <envar>input-device</envar> and
<envar>output-device</envar> OpenPROM variables to
<filename>ttya</filename>.

</para>


  <sect2 id="installer-args"><title>Debian Installer Parameters</title>
<para>

The installation system recognizes a few additional boot parameters<footnote>

<para>

Note that the kernel accepts a maximum of 8 command line options and
8 environment options (including any options added by default for the
installer). If these numbers are exceeded, 2.4 kernels will drop any
excess options and 2.6 kernels will panic.
<phrase condition="etch">With kernel 2.6.9 or newer, you can use 32
command line options and 32 environment options.</phrase>

</para>

</footnote> which may be useful.

</para>

<variablelist>
<varlistentry>
<term>debconf/priority</term>
<listitem><para>

This parameter sets the lowest priority of messages to be displayed.

</para><para>

The default installation uses <userinput>debconf/priority=high</userinput>.
This means that both high and critical priority messages are shown, but medium
and low priority messages are skipped.
If problems are encountered, the installer adjusts the priority as needed.

</para><para>

If you add <userinput>debconf/priority=medium</userinput> as boot parameter, you
will be shown the installation menu and gain more control over the installation.
When <userinput>debconf/priority=low</userinput> is used, all messages are shown
(this is equivalent to the <emphasis>expert</emphasis> boot method).
With <userinput>debconf/priority=critical</userinput>, the installation system
will display only critical messages and try to do the right thing without fuss.

</para></listitem>
</varlistentry>


<varlistentry>
<term>DEBIAN_FRONTEND</term>
<listitem><para>

This boot parameter controls the type of user interface used for the
installer. The current possible parameter settings are:

<itemizedlist>
<listitem>
<para><userinput>DEBIAN_FRONTEND=noninteractive</userinput></para>
</listitem><listitem>
<para><userinput>DEBIAN_FRONTEND=text</userinput></para>
</listitem><listitem>
<para><userinput>DEBIAN_FRONTEND=newt</userinput></para>
</listitem><listitem>
<para><userinput>DEBIAN_FRONTEND=slang</userinput></para>
</listitem><listitem>
<para><userinput>DEBIAN_FRONTEND=ncurses</userinput></para>
</listitem><listitem>
<para><userinput>DEBIAN_FRONTEND=bogl</userinput></para>
</listitem><listitem>
<para><userinput>DEBIAN_FRONTEND=gtk</userinput></para>
</listitem><listitem>
<para><userinput>DEBIAN_FRONTEND=corba</userinput></para>
</listitem>
</itemizedlist>

The default front end is <userinput>DEBIAN_FRONTEND=newt</userinput>.
<userinput>DEBIAN_FRONTEND=text</userinput> may be preferable for
serial console installs. Generally only the
<userinput>newt</userinput> frontend is available on default install
media, so this is not very useful right now.

</para></listitem>
</varlistentry>


<varlistentry>
<term>BOOT_DEBUG</term>
<listitem><para>

Setting this boot parameter to 2 will cause the installer's boot process
to be verbosely logged. Setting it to 3 makes debug shells
available at strategic points in the boot process. (Exit the shells to
continue the boot process.)

<variablelist>
<varlistentry>
<term><userinput>BOOT_DEBUG=0</userinput></term>
<listitem><para>This is the default.</para></listitem>
</varlistentry>

<varlistentry>
<term><userinput>BOOT_DEBUG=1</userinput></term>
<listitem><para>More verbose than usual.</para></listitem>
</varlistentry>

<varlistentry>
<term><userinput>BOOT_DEBUG=2</userinput></term>
<listitem><para>Lots of debugging information.</para></listitem>
</varlistentry>

<varlistentry>
<term><userinput>BOOT_DEBUG=3</userinput></term>
<listitem><para>

Shells are run at various points in the boot process to allow detailed
debugging. Exit the shell to continue the boot.

</para></listitem>
</varlistentry>
</variablelist>

</para></listitem>
</varlistentry>


<varlistentry>
<term>INSTALL_MEDIA_DEV</term>
<listitem><para>

The value of the parameter is the path to the device to load the
Debian installer from. For example,
<userinput>INSTALL_MEDIA_DEV=/dev/floppy/0</userinput>

</para><para>

The boot floppy, which normally scans all floppies and USB storage
devices it can to find the root floppy, can be overridden by this
parameter to only look at the one device.

</para></listitem>
</varlistentry>

<varlistentry>
<term>debian-installer/framebuffer</term>
<listitem><para>

Some architectures use the kernel framebuffer to offer installation in
a number of languages. If framebuffer causes a problem on your system
you can disable the feature by the parameter
<userinput>debian-installer/framebuffer=false</userinput>. Problem
symptoms are error messages about bterm or bogl, a blank screen, or
a freeze within a few minutes after starting the install.

</para><para arch="i386">

The <userinput>video=vga16:off</userinput> argument may also be used
to disable the framebuffer. Such problems have been reported on a Dell
Inspiron with Mobile Radeon card.

</para><para arch="m68k">

Such problems have been reported on the Amiga 1200 and SE/30.

</para><para arch="hppa">

Such problems have been reported on hppa.

</para><note arch="sparc"><para>

Because of display problems on some systems, framebuffer support is
<emphasis>disabled by default</emphasis> for &arch-title;. This can result
in ugly display on systems that do properly support the framebuffer, like
those with ATI graphical cards.
If you see display problems in the installer, you can try booting with
parameter <userinput>debian-installer/framebuffer=true</userinput>.

</para></note></listitem>
</varlistentry>

<varlistentry>
<term>debian-installer/probe/usb</term>
<listitem><para>

Set to <userinput>false</userinput> to prevent probing for USB on
boot, if that causes problems.

</para></listitem>
</varlistentry>

<varlistentry>
<term>netcfg/disable_dhcp</term>
<listitem><para>

By default, the &d-i; automatically probes for network configuration
via DHCP. If the probe succeeds, you won't have a chance to review and
change the obtained settings. You can get to the manual network setup
only in case the DHCP probe fails.

</para><para>

If you have a DHCP server on your local network, but want to avoid it
because e.g. it gives wrong answers, you can use the parameter
<userinput>netcfg/disable_dhcp=true</userinput> to prevent configuring
the network with DHCP and to enter the information manually.

</para></listitem>
</varlistentry>

<varlistentry>
<term>hw-detect/start_pcmcia</term>
<listitem><para>

Set to <userinput>false</userinput> to prevent starting PCMCIA
services, if that causes problems. Some laptops are well known for
this misbehavior.

</para></listitem>
</varlistentry>

<varlistentry>
<term>preseed/url</term>
<listitem><para>

Specify the url to a preconfiguration file to download and use in
automating the install. See <xref linkend="automatic-install"/>.

</para></listitem>
</varlistentry>

<varlistentry>
<term>preseed/file</term>
<listitem><para>

Specify the path to a preconfiguration file to load to
automating the install. See <xref linkend="automatic-install"/>.

</para></listitem>
</varlistentry>

<varlistentry condition="etch">
<term>cdrom-detect/eject</term>
<listitem><para>

By default, before rebooting, &d-i; automatically ejects the optical
media used during the installation. This can be unnecessary if the system
does not automatically boot off the CD. In some cases it may even be
undesirable, for example if the optical drive cannot reinsert the media
itself and the user is not there to do it manually. Many slot loading,
slim-line, and caddy style drives cannot reload media automatically.

</para><para>

Set to <userinput>false</userinput> to disable automatic ejection, and
be aware that you may need to ensure that the system does not
automatically boot from the optical drive after the initial
installation.

</para></listitem>
</varlistentry>

<varlistentry>
<term>ramdisk_size</term>
<listitem><para>

If you are using a 2.2.x kernel, you may need to set &ramdisksize;.

</para></listitem>
</varlistentry>

<varlistentry condition="etch">
<term>rescue/enable</term>
<listitem><para>

Set to <userinput>true</userinput> to enter rescue mode rather than
performing a normal installation. See <xref linkend="rescue"/>.

</para></listitem>
</varlistentry>

</variablelist>
  </sect2>
 </sect1>