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 5.3, “Troubleshooting the Installation Process”.
When the kernel boots, a message
should be emitted early in the process.
total 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
mem=ram parameter,
where ram is set to the amount of memory,
suffixed with “k” for kilobytes, or “m” for
megabytes. For example, both mem=65536k and
mem=64m mean 64MB of RAM.
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=device
argument to the kernel, where device is
your serial device, which is usually something like
ttyS0.
5.2.1. Debian Installer Parameters
The installation system recognizes a few additional boot parameters[4] which may be useful.
- debconf/priority
-
This parameter sets the lowest priority of messages to be displayed.
The default installation uses debconf/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 debconf/priority=medium as boot parameter, you
will be shown the installation menu and gain more control over the installation.
When debconf/priority=low is used, all messages are shown
(this is equivalent to the expert boot method).
With debconf/priority=critical, the installation system
will display only critical messages and try to do the right thing without fuss.
- DEBIAN_FRONTEND
-
This boot parameter controls the type of user interface used for the
installer. The current possible parameter settings are:
The default front end is DEBIAN_FRONTEND=newt.
DEBIAN_FRONTEND=text may be preferable for
serial console installs. Generally only the
newt frontend is available on default install
media, so this is not very useful right now.
- BOOT_DEBUG
-
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=3
Shells are run at various points in the boot process to allow detailed
debugging. Exit the shell to continue the boot.
- INSTALL_MEDIA_DEV
-
The value of the parameter is the path to the device to load the
Debian installer from. For example,
INSTALL_MEDIA_DEV=/dev/floppy/0
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.
- debian-installer/framebuffer
-
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
debian-installer/framebuffer=false. Problem
symptoms are error messages about bterm or bogl, a blank screen, or
a freeze within a few minutes after starting the install.
The video=vga16:off argument may also be used
to disable the framebuffer. Such problems have been reported on a Dell
Inspiron with Mobile Radeon card.
- debian-installer/probe/usb
Set to false to prevent probing for USB on
boot, if that causes problems.
- netcfg/disable_dhcp
-
By default, the debian-installer 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.
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
netcfg/disable_dhcp=true to prevent configuring
the network with DHCP and to enter the information manually.
- hw-detect/start_pcmcia
Set to false to prevent starting PCMCIA
services, if that causes problems. Some laptops are well known for
this misbehavior.
- preseed/url
Specify the url to a preconfiguration file to download and use in
automating the install. See Section 4.7, “Automatic Installation”.
- preseed/file
Specify the path to a preconfiguration file to load to
automating the install. See Section 4.7, “Automatic Installation”.
- ramdisk_size
If you are using a 2.2.x kernel, you may need to set
ramdisk_size=13000
.
