<!DOCTYPE html>
<html lang="en" data-content_root="../">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" />
<title>The Framebuffer Console — The Linux Kernel documentation</title>
<link rel="stylesheet" type="text/css" href="../_static/pygments.css?v=fa44fd50" />
<link rel="stylesheet" type="text/css" href="../_static/alabaster.css?v=3918102e" />
<script src="../_static/documentation_options.js?v=5929fcd5"></script>
<script src="../_static/doctools.js?v=9bcbadda"></script>
<script src="../_static/sphinx_highlight.js?v=dc90522c"></script>
<link rel="index" title="Index" href="../genindex.html" />
<link rel="search" title="Search" href="../search.html" />
<link rel="next" title="The Frame Buffer Device" href="framebuffer.html" />
<link rel="prev" title="Deferred IO" href="deferred_io.html" />
<link rel="stylesheet" href="../_static/custom.css" type="text/css" />
</head><body>
<div class="document">
<div class="sphinxsidebar" role="navigation" aria-label="Main">
<div class="sphinxsidebarwrapper">
<p class="logo"><a href="../index.html">
<img class="logo" src="../_static/logo.svg" alt="Logo of The Linux Kernel"/>
</a></p>
<h1 class="logo"><a href="../index.html">The Linux Kernel</a></h1>
<p class="blurb">6.18.50</p>
<search id="searchbox" style="display: none" role="search">
<h3 id="searchlabel">Quick search</h3>
<div class="searchformwrapper">
<form class="search" action="../search.html" method="get">
<input type="text" name="q" aria-labelledby="searchlabel" autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false"/>
<input type="submit" value="Go" />
</form>
</div>
</search>
<script>document.getElementById('searchbox').style.display = "block"</script>
<p>
<h3 class="kernel-toc-contents">Contents</h3>
<input type="checkbox" class="kernel-toc-toggle" id = "kernel-toc-toggle" checked>
<label class="kernel-toc-title" for="kernel-toc-toggle"></label>
<div class="kerneltoc" id="kerneltoc">
<ul>
<li class="toctree-l1"><a class="reference internal" href="../process/development-process.html">Development process</a></li>
<li class="toctree-l1"><a class="reference internal" href="../process/submitting-patches.html">Submitting patches</a></li>
<li class="toctree-l1"><a class="reference internal" href="../process/code-of-conduct.html">Code of conduct</a></li>
<li class="toctree-l1"><a class="reference internal" href="../maintainer/index.html">Maintainer handbook</a></li>
<li class="toctree-l1"><a class="reference internal" href="../process/index.html">All development-process docs</a></li>
</ul>
<ul class="current">
<li class="toctree-l1"><a class="reference internal" href="../core-api/index.html">Core API</a></li>
<li class="toctree-l1"><a class="reference internal" href="../driver-api/index.html">Driver APIs</a></li>
<li class="toctree-l1 current"><a class="reference internal" href="../subsystem-apis.html">Subsystems</a><ul class="current">
<li class="toctree-l2"><a class="reference internal" href="../subsystem-apis.html#core-subsystems">Core subsystems</a></li>
<li class="toctree-l2 current"><a class="reference internal" href="../subsystem-apis.html#human-interfaces">Human interfaces</a><ul class="current">
<li class="toctree-l3"><a class="reference internal" href="../input/index.html">Input Documentation</a></li>
<li class="toctree-l3"><a class="reference internal" href="../hid/index.html">Human Interface Devices (HID)</a></li>
<li class="toctree-l3"><a class="reference internal" href="../sound/index.html">Sound Subsystem Documentation</a></li>
<li class="toctree-l3"><a class="reference internal" href="../gpu/index.html">GPU Driver Developer’s Guide</a></li>
<li class="toctree-l3 current"><a class="reference internal" href="index.html">Frame Buffer</a></li>
<li class="toctree-l3"><a class="reference internal" href="../leds/index.html">LEDs</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="../subsystem-apis.html#networking-interfaces">Networking interfaces</a></li>
<li class="toctree-l2"><a class="reference internal" href="../subsystem-apis.html#storage-interfaces">Storage interfaces</a></li>
<li class="toctree-l2"><a class="reference internal" href="../subsystem-apis.html#other-subsystems">Other subsystems</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../locking/index.html">Locking</a></li>
</ul>
<ul>
<li class="toctree-l1"><a class="reference internal" href="../process/license-rules.html">Licensing rules</a></li>
<li class="toctree-l1"><a class="reference internal" href="../doc-guide/index.html">Writing documentation</a></li>
<li class="toctree-l1"><a class="reference internal" href="../dev-tools/index.html">Development tools</a></li>
<li class="toctree-l1"><a class="reference internal" href="../dev-tools/testing-overview.html">Testing guide</a></li>
<li class="toctree-l1"><a class="reference internal" href="../kernel-hacking/index.html">Hacking guide</a></li>
<li class="toctree-l1"><a class="reference internal" href="../trace/index.html">Tracing</a></li>
<li class="toctree-l1"><a class="reference internal" href="../fault-injection/index.html">Fault injection</a></li>
<li class="toctree-l1"><a class="reference internal" href="../livepatch/index.html">Livepatching</a></li>
<li class="toctree-l1"><a class="reference internal" href="../rust/index.html">Rust</a></li>
</ul>
<ul>
<li class="toctree-l1"><a class="reference internal" href="../admin-guide/index.html">Administration</a></li>
<li class="toctree-l1"><a class="reference internal" href="../kbuild/index.html">Build system</a></li>
<li class="toctree-l1"><a class="reference internal" href="../admin-guide/reporting-issues.html">Reporting issues</a></li>
<li class="toctree-l1"><a class="reference internal" href="../tools/index.html">Userspace tools</a></li>
<li class="toctree-l1"><a class="reference internal" href="../userspace-api/index.html">Userspace API</a></li>
</ul>
<ul>
<li class="toctree-l1"><a class="reference internal" href="../firmware-guide/index.html">Firmware</a></li>
<li class="toctree-l1"><a class="reference internal" href="../devicetree/index.html">Firmware and Devicetree</a></li>
</ul>
<ul>
<li class="toctree-l1"><a class="reference internal" href="../arch/index.html">CPU architectures</a></li>
</ul>
<ul>
<li class="toctree-l1"><a class="reference internal" href="../staging/index.html">Unsorted documentation</a></li>
</ul>
<ul>
<li class="toctree-l1"><a class="reference internal" href="../translations/index.html">Translations</a></li>
</ul>
</div>
<script type="text/javascript"> <!--
var sbar = document.getElementsByClassName("sphinxsidebar")[0];
let currents = document.getElementsByClassName("current")
if (currents.length) {
sbar.scrollTop = currents[currents.length - 1].offsetTop;
}
--> </script>
<div role="note" aria-label="source link">
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="../_sources/fb/fbcon.rst.txt"
rel="nofollow">Show Source</a></li>
</ul>
</div>
</div>
</div>
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body" role="main">
<section id="the-framebuffer-console">
<h1>The Framebuffer Console<a class="headerlink" href="#the-framebuffer-console" title="Link to this heading">¶</a></h1>
<p>The framebuffer console (fbcon), as its name implies, is a text
console running on top of the framebuffer device. It has the functionality of
any standard text console driver, such as the VGA console, with the added
features that can be attributed to the graphical nature of the framebuffer.</p>
<p>In the x86 architecture, the framebuffer console is optional, and
some even treat it as a toy. For other architectures, it is the only available
display device, text or graphical.</p>
<p>What are the features of fbcon? The framebuffer console supports
high resolutions, varying font types, display rotation, primitive multihead,
etc. Theoretically, multi-colored fonts, blending, aliasing, and any feature
made available by the underlying graphics card are also possible.</p>
<section id="a-configuration">
<h2>A. Configuration<a class="headerlink" href="#a-configuration" title="Link to this heading">¶</a></h2>
<p>The framebuffer console can be enabled by using your favorite kernel
configuration tool. It is under Device Drivers->Graphics Support->
Console display driver support->Framebuffer Console Support.
Select ‘y’ to compile support statically or ‘m’ for module support. The
module will be fbcon.</p>
<p>In order for fbcon to activate, at least one framebuffer driver is
required, so choose from any of the numerous drivers available. For x86
systems, they almost universally have VGA cards, so vga16fb and vesafb will
always be available. However, using a chipset-specific driver will give you
more speed and features, such as the ability to change the video mode
dynamically.</p>
<p>To display the penguin logo, choose any logo available in Graphics
support->Bootup logo.</p>
<p>Also, you will need to select at least one compiled-in font, but if
you don’t do anything, the kernel configuration tool will select one for you,
usually an 8x16 font.</p>
<div class="admonition-gotcha admonition">
<p class="admonition-title">GOTCHA</p>
<p>A common bug report is enabling the framebuffer without enabling the
framebuffer console. Depending on the driver, you may get a blanked or
garbled display, but the system still boots to completion. If you are
fortunate to have a driver that does not alter the graphics chip, then you
will still get a VGA console.</p>
</div>
</section>
<section id="b-loading">
<h2>B. Loading<a class="headerlink" href="#b-loading" title="Link to this heading">¶</a></h2>
<p>Possible scenarios:</p>
<ol class="arabic">
<li><p>Driver and fbcon are compiled statically</p>
<blockquote>
<div><p>Usually, fbcon will automatically take over your console. The notable
exception is vesafb. It needs to be explicitly activated with the
vga= boot option parameter.</p>
</div></blockquote>
</li>
<li><p>Driver is compiled statically, fbcon is compiled as a module</p>
<blockquote>
<div><p>Depending on the driver, you either get a standard console, or a
garbled display, as mentioned above. To get a framebuffer console,
do a ‘modprobe fbcon’.</p>
</div></blockquote>
</li>
<li><p>Driver is compiled as a module, fbcon is compiled statically</p>
<blockquote>
<div><p>You get your standard console. Once the driver is loaded with
‘modprobe xxxfb’, fbcon automatically takes over the console with
the possible exception of using the fbcon=map:n option. See below.</p>
</div></blockquote>
</li>
<li><p>Driver and fbcon are compiled as a module.</p>
<blockquote>
<div><p>You can load them in any order. Once both are loaded, fbcon will take
over the console.</p>
</div></blockquote>
</li>
</ol>
</section>
<section id="c-boot-options">
<h2>C. Boot options<a class="headerlink" href="#c-boot-options" title="Link to this heading">¶</a></h2>
<blockquote>
<div><p>The framebuffer console has several, largely unknown, boot options
that can change its behavior.</p>
</div></blockquote>
<ol class="arabic">
<li><p>fbcon=font:<name></p>
<blockquote>
<div><p>Select the initial font to use. The value ‘name’ can be any of the
compiled-in fonts: 10x18, 6x10, 6x8, 7x14, Acorn8x8, MINI4x6,
PEARL8x8, ProFont6x11, SUN12x22, SUN8x16, TER16x32, VGA8x16, VGA8x8.</p>
<p>Note, not all drivers can handle font with widths not divisible by 8,
such as vga16fb.</p>
</div></blockquote>
</li>
<li><p>fbcon=map:<0123></p>
<blockquote>
<div><p>This is an interesting option. It tells which driver gets mapped to
which console. The value ‘0123’ is a sequence that gets repeated until
the total length is 64 which is the number of consoles available. In
the above example, it is expanded to 012301230123... and the mapping
will be:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>tty | 1 2 3 4 5 6 7 8 9 ...
fb | 0 1 2 3 0 1 2 3 0 ...
('cat /proc/fb' should tell you what the fb numbers are)
</pre></div>
</div>
<p>One side effect that may be useful is using a map value that exceeds
the number of loaded fb drivers. For example, if only one driver is
available, fb0, adding fbcon=map:1 tells fbcon not to take over the
console.</p>
<p>Later on, when you want to map the console the to the framebuffer
device, you can use the con2fbmap utility.</p>
</div></blockquote>
</li>
<li><p>fbcon=vc:<n1>-<n2></p>
<blockquote>
<div><p>This option tells fbcon to take over only a range of consoles as
specified by the values ‘n1’ and ‘n2’. The rest of the consoles
outside the given range will still be controlled by the standard
console driver.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>For x86 machines, the standard console is the VGA console which
is typically located on the same video card. Thus, the consoles that
are controlled by the VGA console will be garbled.</p>
</div>
</div></blockquote>
</li>
<li><p>fbcon=rotate:<n></p>
<blockquote>
<div><p>This option changes the orientation angle of the console display. The
value ‘n’ accepts the following:</p>
<blockquote>
<div><ul class="simple">
<li><p>0 - normal orientation (0 degree)</p></li>
<li><p>1 - clockwise orientation (90 degrees)</p></li>
<li><p>2 - upside down orientation (180 degrees)</p></li>
<li><p>3 - counterclockwise orientation (270 degrees)</p></li>
</ul>
</div></blockquote>
<p>The angle can be changed anytime afterwards by ‘echoing’ the same
numbers to any one of the 2 attributes found in
/sys/class/graphics/fbcon:</p>
<blockquote>
<div><ul class="simple">
<li><p>rotate - rotate the display of the active console</p></li>
<li><p>rotate_all - rotate the display of all consoles</p></li>
</ul>
</div></blockquote>
<p>Console rotation will only become available if Framebuffer Console
Rotation support is compiled in your kernel.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>This is purely console rotation. Any other applications that
use the framebuffer will remain at their ‘normal’ orientation.
Actually, the underlying fb driver is totally ignorant of console
rotation.</p>
</div>
</div></blockquote>
</li>
<li><p>fbcon=margin:<color></p>
<blockquote>
<div><p>This option specifies the color of the margins. The margins are the
leftover area at the right and the bottom of the screen that are not
used by text. By default, this area will be black. The ‘color’ value
is an integer number that depends on the framebuffer driver being used.</p>
</div></blockquote>
</li>
<li><p>fbcon=nodefer</p>
<blockquote>
<div><p>If the kernel is compiled with deferred fbcon takeover support, normally
the framebuffer contents, left in place by the firmware/bootloader, will
be preserved until there actually is some text is output to the console.
This option causes fbcon to bind immediately to the fbdev device.</p>
</div></blockquote>
</li>
<li><p>fbcon=logo-pos:<location></p>
<blockquote>
<div><p>The only possible ‘location’ is ‘center’ (without quotes), and when
given, the bootup logo is moved from the default top-left corner
location to the center of the framebuffer. If more than one logo is
displayed due to multiple CPUs, the collected line of logos is moved
as a whole.</p>
</div></blockquote>
</li>
<li><p>fbcon=logo-count:<n></p>
<blockquote>
<div><p>The value ‘n’ overrides the number of bootup logos. 0 disables the
logo, and -1 gives the default which is the number of online CPUs.</p>
</div></blockquote>
</li>
</ol>
</section>
<section id="d-attaching-detaching-and-unloading">
<h2>D. Attaching, Detaching and Unloading<a class="headerlink" href="#d-attaching-detaching-and-unloading" title="Link to this heading">¶</a></h2>
<p>Before going on to how to attach, detach and unload the framebuffer console, an
illustration of the dependencies may help.</p>
<p>The console layer, as with most subsystems, needs a driver that interfaces with
the hardware. Thus, in a VGA console:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>console ---> VGA driver ---> hardware.
</pre></div>
</div>
<p>Assuming the VGA driver can be unloaded, one must first unbind the VGA driver
from the console layer before unloading the driver. The VGA driver cannot be
unloaded if it is still bound to the console layer. (See
<a class="reference internal" href="../driver-api/console.html"><span class="doc">Console Drivers</span></a> for more information).</p>
<p>This is more complicated in the case of the framebuffer console (fbcon),
because fbcon is an intermediate layer between the console and the drivers:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>console ---> fbcon ---> fbdev drivers ---> hardware
</pre></div>
</div>
<p>The fbdev drivers cannot be unloaded if bound to fbcon, and fbcon cannot
be unloaded if it’s bound to the console layer.</p>
<p>So to unload the fbdev drivers, one must first unbind fbcon from the console,
then unbind the fbdev drivers from fbcon. Fortunately, unbinding fbcon from
the console layer will automatically unbind framebuffer drivers from
fbcon. Thus, there is no need to explicitly unbind the fbdev drivers from
fbcon.</p>
<p>So, how do we unbind fbcon from the console? Part of the answer is in
<a class="reference internal" href="../driver-api/console.html"><span class="doc">Console Drivers</span></a>. To summarize:</p>
<p>Echo a value to the bind file that represents the framebuffer console
driver. So assuming vtcon1 represents fbcon, then:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>echo 1 > /sys/class/vtconsole/vtcon1/bind - attach framebuffer console to
console layer
echo 0 > /sys/class/vtconsole/vtcon1/bind - detach framebuffer console from
console layer
</pre></div>
</div>
<p>If fbcon is detached from the console layer, your boot console driver (which is
usually VGA text mode) will take over. A few drivers (rivafb and i810fb) will
restore VGA text mode for you. With the rest, before detaching fbcon, you
must take a few additional steps to make sure that your VGA text mode is
restored properly. The following is one of the several methods that you can do:</p>
<ol class="arabic">
<li><p>Download or install vbetool. This utility is included with most
distributions nowadays, and is usually part of the suspend/resume tool.</p></li>
<li><p>In your kernel configuration, ensure that CONFIG_FRAMEBUFFER_CONSOLE is set
to ‘y’ or ‘m’. Enable one or more of your favorite framebuffer drivers.</p></li>
<li><p>Boot into text mode and as root run:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>vbetool vbestate save > <vga state file>
</pre></div>
</div>
<p>The above command saves the register contents of your graphics
hardware to <vga state file>. You need to do this step only once as
the state file can be reused.</p>
</li>
<li><p>If fbcon is compiled as a module, load fbcon by doing:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>modprobe fbcon
</pre></div>
</div>
</li>
<li><p>Now to detach fbcon:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>vbetool vbestate restore < <vga state file> && \
echo 0 > /sys/class/vtconsole/vtcon1/bind
</pre></div>
</div>
</li>
<li><p>That’s it, you’re back to VGA mode. And if you compiled fbcon as a module,
you can unload it by ‘rmmod fbcon’.</p></li>
<li><p>To reattach fbcon:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>echo 1 > /sys/class/vtconsole/vtcon1/bind
</pre></div>
</div>
</li>
<li><p>Once fbcon is unbound, all drivers registered to the system will also
become unbound. This means that fbcon and individual framebuffer drivers
can be unloaded or reloaded at will. Reloading the drivers or fbcon will
automatically bind the console, fbcon and the drivers together. Unloading
all the drivers without unloading fbcon will make it impossible for the
console to bind fbcon.</p></li>
</ol>
</section>
<section id="notes-for-vesafb-users">
<h2>Notes for vesafb users:<a class="headerlink" href="#notes-for-vesafb-users" title="Link to this heading">¶</a></h2>
<p>Unfortunately, if your bootline includes a vga=xxx parameter that sets the
hardware in graphics mode, such as when loading vesafb, vgacon will not load.
Instead, vgacon will replace the default boot console with dummycon, and you
won’t get any display after detaching fbcon. Your machine is still alive, so
you can reattach vesafb. However, to reattach vesafb, you need to do one of
the following:</p>
<p>Variation 1:</p>
<blockquote>
<div><ol class="loweralpha">
<li><p>Before detaching fbcon, do:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>vbetool vbemode save > <vesa state file> # do once for each vesafb mode,
# the file can be reused
</pre></div>
</div>
</li>
<li><p>Detach fbcon as in step 5.</p></li>
<li><p>Attach fbcon:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>vbetool vbestate restore < <vesa state file> && \
echo 1 > /sys/class/vtconsole/vtcon1/bind
</pre></div>
</div>
</li>
</ol>
</div></blockquote>
<p>Variation 2:</p>
<blockquote>
<div><ol class="loweralpha">
<li><p>Before detaching fbcon, do:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>echo <ID> > /sys/class/tty/console/bind
vbetool vbemode get
</pre></div>
</div>
</li>
<li><p>Take note of the mode number</p></li>
</ol>
<ol class="loweralpha" start="2">
<li><p>Detach fbcon as in step 5.</p></li>
<li><p>Attach fbcon:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>vbetool vbemode set <mode number> && \
echo 1 > /sys/class/vtconsole/vtcon1/bind
</pre></div>
</div>
</li>
</ol>
</div></blockquote>
</section>
<section id="samples">
<h2>Samples:<a class="headerlink" href="#samples" title="Link to this heading">¶</a></h2>
<p>Here are 2 sample bash scripts that you can use to bind or unbind the
framebuffer console driver if you are on an X86 box:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>#!/bin/bash
# Unbind fbcon
# Change this to where your actual vgastate file is located
# Or Use VGASTATE=$1 to indicate the state file at runtime
VGASTATE=/tmp/vgastate
# path to vbetool
VBETOOL=/usr/local/bin
for (( i = 0; i < 16; i++))
do
if test -x /sys/class/vtconsole/vtcon$i; then
if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \
= 1 ]; then
if test -x $VBETOOL/vbetool; then
echo Unbinding vtcon$i
$VBETOOL/vbetool vbestate restore < $VGASTATE
echo 0 > /sys/class/vtconsole/vtcon$i/bind
fi
fi
fi
done
</pre></div>
</div>
<hr class="docutils" />
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>#!/bin/bash
# Bind fbcon
for (( i = 0; i < 16; i++))
do
if test -x /sys/class/vtconsole/vtcon$i; then
if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \
= 1 ]; then
echo Unbinding vtcon$i
echo 1 > /sys/class/vtconsole/vtcon$i/bind
fi
fi
done
</pre></div>
</div>
<p>Antonino Daplas <<a class="reference external" href="mailto:adaplas%40pol.net">adaplas<span>@</span>pol<span>.</span>net</a>></p>
</section>
</section>
</div>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="footer">
©The kernel development community.
|
Powered by <a href="https://www.sphinx-doc.org/">Sphinx 8.1.3</a>
& <a href="https://alabaster.readthedocs.io">Alabaster 0.7.16</a>
|
<a href="../_sources/fb/fbcon.rst.txt"
rel="nofollow">Page source</a>
</div>
</body>
</html>