| 5.3. Boot Parameters | ||
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Chapter 5. Booting the Installation System | 
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| 5.3. Boot Parameters | ||
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Chapter 5. Booting the Installation System |
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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.
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.
Information on many boot parameters can be found in the Linux BootPrompt HOWTO, including tips for obscure hardware. This section contains only a sketch of the most salient parameters. Some common gotchas are included below in Section 5.4, “Troubleshooting the Installation Process”.
If you are booting with a serial console, generally the kernel will
autodetect this.
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
console=
argument to the kernel, where devicedevice is
a serial device of the target, which is usually something like
ttyS0.
You may need to specify parameters for the serial port, such as speed and
parity, for instance console=ttyS0,9600n8; other typical
speeds may be 57600 or 115200. Be sure to specify this option after
“---”, so that it is copied into the bootloader configuration for
the installed system (if supported by the installer for the bootloader).
In order to ensure the terminal type used by the installer matches your
terminal emulator, the parameter
TERM= can be added.
Note that the installer only supports the following terminal types:
typelinux, bterm, ansi,
vt102 and dumb. The default for
serial console in debian-installer is vt102. If you are using an IPMI console, or a
virtualization tool which does not provide conversion into such terminals types
itself, e.g. QEMU/KVM, you can start it inside a screen
session. That will indeed perform translation into the screen
terminal type, which is very close to vt102.
The installation system recognizes a few additional boot parameters[2] which may be useful.
A number of parameters have a “short form” that helps avoid the limitations of the kernel command line options and makes entering the parameters easier. If a parameter has a short form, it will be listed in brackets behind the (normal) long form. Examples in this manual will normally use the short form too.
This parameter sets the lowest priority of messages to be displayed.
The default installation uses priority=high.
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.
If you add priority=medium as boot parameter, you
will be shown the installation menu and gain more control over the installation.
When priority=low is used, all messages are shown
(this is equivalent to the expert boot method).
With priority=critical, the installation system
will display only critical messages and try to do the right thing without fuss.
This boot parameter controls the type of user interface used for the installer. The current possible parameter settings are:
DEBIAN_FRONTEND=noninteractive
DEBIAN_FRONTEND=text
DEBIAN_FRONTEND=newt
DEBIAN_FRONTEND=gtk
The default frontend is DEBIAN_FRONTEND=newt.
DEBIAN_FRONTEND=text may be preferable for
serial console installs. Some specialized types of install media may
only offer a limited selection of frontends, but the
newt and text frontends
are available on most default install media.
On architectures that support it, the graphical installer uses
the gtk frontend.
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.)
BOOT_DEBUG=0This is the default.
BOOT_DEBUG=1More verbose than usual.
BOOT_DEBUG=2Lots of debugging information.
BOOT_DEBUG=3Shells are run at various points in the boot process to allow detailed debugging. Exit the shell to continue the boot.
Causes the installer to send log messages to a remote syslog on the specified host and port as well as to a local file. If not specified, the port defaults to the standard syslog port 514.
Can be used to force the installer to a lowmem level higher than the one the installer sets by default based on available memory. Possible values are 1 and 2. See also Section 6.3.1.1, “Check available memory / low memory mode”.
Prevents the installer from offering interactive shells on tty2 and tty3. Useful for unattended installations where physical security is limited.
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 using the parameter
fb=false.
Problem symptoms are error messages about bterm or bogl, a blank screen,
or a freeze within a few minutes after starting the install.
A theme determines how the user interface of the installer looks (colors,
icons, etc.). Which themes are available may differ per frontend. Currently
both the newt and gtk frontend have (apart from the default look) only
one additional theme named “dark” theme, which was
designed for visually impaired users. Set this theme by booting with
theme=
(there is also the keyboard shortcut darkd for this
in the boot menu).
By default, the debian-installer automatically probes for network configuration
via IPv6 autoconfiguration and 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 automatic configuration fails.
If you have an IPv6 router or a DHCP server on your local network, but want to avoid them
because e.g. they give wrong answers, you can use the parameter
netcfg/disable_autoconfig=true to prevent any automatic
configuration of the network (neither v4 nor v6) and to enter the information manually.
Set to false to prevent starting PCMCIA
services, if that causes problems. Some laptops are well known for
this misbehavior.
Specify the url to a preconfiguration file to download and use for automating the install. See Section 4.4, “Automatic Installation”.
Specify the path to a preconfiguration file to load for automating the install. See Section 4.4, “Automatic Installation”.
Set to true to display questions even if they have
been preseeded. Can be useful for testing or debugging a preconfiguration
file. Note that this will have no effect on parameters that are passed as
boot parameters, but for those a special syntax can be used.
See Section B.5.2, “Using preseeding to change default values” for details.
Delay questions that are normally asked before preseeding is possible until after the network is configured. See Section B.2.3, “Auto mode” for details about using this to automate installs.
During installations from serial or management console, the regular
virtual consoles (VT1 to VT6) are normally disabled in
/etc/inittab.
Set to true to prevent this.
By default, before rebooting, debian-installer automatically ejects the optical
media used during the installation. This can be unnecessary if the system
does not automatically boot off such media. 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.
Set to false 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.
By setting this option to false, the package
management system will be configured to not automatically install
“Recommends”, both during the installation and for the
installed system. See also Section 6.3.5, “Installing the Base System”.
Note that this option allows to have a leaner system, but can also result in features being missing that you might normally expect to be available. You may have to manually install some of the recommended packages to obtain the full functionality you want. This option should therefore only be used by very experienced users.
By default the installer requires that repositories be authenticated
using a known gpg key. Set to true to
disable that authentication.
Warning: insecure, not recommended.
Set to true to enter rescue mode rather than
performing a normal installation. See Section 8.6, “Recovering a Broken System”.
With some exceptions, a value can be set at the boot prompt for any question asked during the installation, though this is only really useful in specific cases. General instructions how to do this can be found in Section B.2.2, “Using boot parameters to preseed questions”. Some specific examples are listed below.
There are two ways to specify the language, country and locale to use for the installation and the installed system.
The first and easiest is to pass only the parameter locale.
Language and country will then be derived from its value. You can for example
use locale=de_CH to select German as language and
Switzerland as country (de_CH.UTF-8 will be set as default
locale for the installed system). Limitation is that not all possible
combinations of language, country and locale can be achieved this way.
The second, more flexible option is to specify language
and country separately. In this case
locale can optionally be added to specify a specific
default locale for the installed system. Example:
language=en country=DE locale=en_GB.UTF-8.
Can be used to automatically load installer components that are not loaded
by default.
Examples of optional components that may be useful are
openssh-client-udeb (so you can use
scp during the installation) and
ppp-udeb (see Section D.4, “Installing Debian GNU/Linux using PPP over Ethernet (PPPoE)”).
Set to true if you want to disable IPv6 autoconfiguration
and DHCP and instead force static network configuration.
By default the installer will use the http protocol to download files from
Debian mirrors and changing that to ftp is not possible during installations
at normal priority. By setting this parameter to ftp,
you can force the installer to use that protocol instead. Note that you
cannot select an ftp mirror from a list, you have to enter the hostname
manually.
Can be used to select tasks that are not available from the interactive task
list, such as the kde-desktop task.
See Section 6.3.6.2, “Selecting and Installing Software” for additional information.
If drivers are compiled into the kernel, you can pass parameters to them as described in the kernel documentation. However, if drivers are compiled as modules and because kernel modules are loaded a bit differently during an installation than when booting an installed system, it is not possible to pass parameters to modules as you would normally do. Instead, you need to use a special syntax recognized by the installer which will then make sure that the parameters are saved in the proper configuration files and will thus be used when the modules are actually loaded. The parameters will also be propagated automatically to the configuration for the installed system.
Note that it is now quite rare that parameters need to be passed to modules. In most cases the kernel will be able to probe the hardware present in a system and set good defaults that way. However, in some situations it may still be needed to set parameters manually.
The syntax to use to set parameters for modules is:
module_name.parameter_name=value
If you need to pass multiple parameters to the same or different modules, just repeat this. For example, to set an old 3Com network interface card to use the BNC (coax) connector and IRQ 10, you would pass:
3c509.xcvr=3 3c509.irq=10
Sometimes it may be necessary to blacklist a module to prevent it from being loaded automatically by the kernel and udev. One reason could be that a particular module causes problems with your hardware. The kernel also sometimes lists two different drivers for the same device. This can cause the device to not work correctly if the drivers conflict or if the wrong driver is loaded first.
You can blacklist a module using the following syntax:
module_name.blacklist=yes/etc/modprobe.d/blacklist.local both during the
installation and for the installed system.
Note that a module may still be loaded by the installation system itself. You can prevent that from happening by running the installation in expert mode and unselecting the module from the list of modules displayed during the hardware detection phases.
[2] With current kernels (2.6.9 or newer) you can use 32 command line options and 32 environment options. If these numbers are exceeded, the kernel will panic. Also there is a limit of 255 characters for the whole kernel command line, everything above this limit may be silently truncated.
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| 5.2. Accessibility |  |
5.4. Troubleshooting the Installation Process |