Mode-Setting

Under mode-setting is meant to set the display resolution and color depth of the video card by software. Modern fashion -setting software along with hot-plugging, also supports the use of multiple monitors (so-called multi-head operation).

Variants of the mode-setting

The mode setting can be done both in kernel space and user-space.

Mode setting in the user space

On Linux and BSD is traditionally the X Window System takes care of this part, that is, the mode-setting happens in user space. Before the X server is started, the graphics card is usually operated in a text mode, which is normally set via the kernel parameter "vga ". Reaches the operating system a certain runlevel (usually 5 in Debian, for example, but 3), the X server is started.

Benefits

  • The displacement of the graphics card in a text mode is much easier to accomplish; so are the chances of success higher (especially after changing the video card and / or monitor if the new hardware other parameters required). If the graphical server no longer starts or the screen stays black (eg because a wrong resolution or refresh rate is set to false ), one has then to text mode to record, for example, required driver or change the configuration files. In most cases the operating system provides a "recovery mode ", in which the graphical server does not start to fulfill these tasks.

Disadvantages

  • The switch from text mode which was set at the start of the kernel, in the graphics mode leads many monitors to the fact that short-term picture does not appear. In CRT monitors also noise may occur. This happens both when the operating system when starting the graphical server is started for the first time, as well as the graphical Server is stopped or a new graphical server is started on another virtual terminal and switches to this ( eg in the course of the fast - User Switchings ). Similarly, is usually terminated at shutdown the graphical server and switched back to text mode.
  • The direct hardware access software in user space requires elevated privileges, which is not desirable from a security perspective.

Mode setting in the kernel space

In kernel mode-setting, as it dominates the Linux kernel since version 2.6.28 for some graphics card models, already the kernel takes over the adjustment of the graphics card.

Benefits

  • Faster switching between multiple concurrent graphical servers (for example, as part of the Fast User Switchings ), since no mode-setting takes place when both sessions are using the same parameters.
  • No flickering of the monitor when switching between multiple graphical servers.
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