5.2. Boot Parameters
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## 5.2. Boot Parameters

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 Install Process”.

When the kernel boots, a message

    Memory:availk/totalk available

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[3] which may be useful.

debconf/priority

  This parameter settings will set the highest 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:

  - `DEBIAN_FRONTEND=noninteractive`

  - `DEBIAN_FRONTEND=text`

  - `DEBIAN_FRONTEND=newt`

  - `DEBIAN_FRONTEND=slang`

  - `DEBIAN_FRONTEND=ncurses`

  - `DEBIAN_FRONTEND=bogl`

  - `DEBIAN_FRONTEND=gtk`

  - `DEBIAN_FRONTEND=corba`

  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

  Passing this boot parameter will cause the boot to be more verbosely logged.

  `BOOT_DEBUG=0`

    This is the default.

  `BOOT_DEBUG=1`

    More verbose than usual.

  `BOOT_DEBUG=2`

    Lots 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.

  Such problems have been reported on hppa.

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 4.4, “Automatic Installation”.

preseed/file

  Specify the url to a preconfiguration file to load to automating the install. See Section 4.4, “Automatic Installation”.

ramdisk_size

  If you are using a 2.2.x kernel, you may need to set `ramdisk_size=13000` .

[3] 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.

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