6.1. How the Installer Works
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## 6.1. How the Installer Works

The Debian Installer consists of a number of special-purpose components to perform each installation task. Each component performs its task, asking the user questions as necessary to do its job. The questions themselves are given priorities, and the priority of questions to be asked is set when the installer is started.

When a default installation is performed, only essential (high priority) questions will be asked. This results in a highly automated installation process with little user interaction. Components are automatically run in sequence; which components are run depends mainly on the installation method you use and on your hardware. The installer will use default values for questions that are not asked.

If there is a problem, the user will see an error screen, and the installer menu may be shown in order to select some alternative action. If there are no problems, the user will never see the installer menu, but will simply answer questions for each component in turn. Serious error notifications are set to priority 'critical' so the user will always be notified.

Some of the defaults that the installer uses can be influenced by passing boot arguments when `debian-installer` is started. If, for example, you wish to force static network configuration (DHCP is used by default if available), you could add the boot parameter `netcfg/disable_dhcp=true`. See Section 5.2.1, “Debian Installer Parameters” for available options.

Power users may be more comfortable with a menu-driven interface, where each step is controlled by the user rather than the installer performing each step automatically in sequence. To use the installer in a manual, menu-driven way, add the boot argument `debconf/priority=medium`.

If your hardware requires you to pass options to kernel modules as they are installed, you will need to start the installer in “expert” mode. This can be done by either using the expert command to start the installer or by adding the boot argument `debconf/priority=low`. Expert mode gives you full control over `debian-installer`.

The normal installer display is character-based (as opposed to the now more familiar graphical interface). The mouse is not operational in this environment. Here are the keys you can use to navigate within the various dialogs. The Tab or right arrow keys move `forward', and the Shift-Tab or left arrow keys move `backward' between displayed buttons and selections. The up and down arrow select different items within a scrollable list, and also scroll the list itself. In addition, in long lists, you can type a letter to cause the list to scroll directly to the section with items starting with the letter you typed and use Pg-Up and Pg-Down to scroll the list in sections. The space bar selects an item such as a checkbox. Use Enter to activate choices.

Error messages are redirected to the third console. You can access this console by pressing Left Alt-F3 (hold the left Alt key while pressing the F3 function key); get back to the main installer process with Left Alt-F1.

These messages can also be found in `/var/log/messages`. After installation, this log is copied to `/var/log/debian-installer/messages` on your new system. Other installation messages may be found in `/var/log/` during the installation, and `/var/log/debian-installer/` after the computer has been booted into the installed system.

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