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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<TITLE>User Mode Linux HOWTO : Introduction</TITLE>
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<H2><A NAME="intro"></A> <A NAME="s1">1.</A> <A HREF="UserModeLinux-HOWTO.html#toc1">Introduction</A></H2>
<P>Welcome to User Mode Linux. It's going to be fun.</P>
<H2><A NAME="ss1.1">1.1</A> <A HREF="UserModeLinux-HOWTO.html#toc1.1">How is User Mode Linux Different?</A>
</H2>
<P>Normally, the Linux Kernel talks straight to your hardware (video
card, keyboard, hard drives, etc), and any programs which run ask the
kernel to operate the hardware, like so:</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
+-----------+-----------+----+
| Process 1 | Process 2 | ...|
+-----------+-----------+----+
| Linux Kernel |
+----------------------------+
| Hardware |
+----------------------------+
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P>The User Mode Linux Kernel is different; instead of talking to the
hardware, it talks to a `real' Linux kernel (called the `host kernel'
from now on), like any other program. Programs can then run inside
User-Mode Linux as if they were running under a normal kernel, like
so:</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
+----------------+
| Process 2 | ...|
+-----------+----------------+
| Process 1 | User-Mode Linux|
+----------------------------+
| Linux Kernel |
+----------------------------+
| Hardware |
+----------------------------+
</PRE>
</CODE></BLOCKQUOTE>
</P>
<H2><A NAME="ss1.2">1.2</A> <A HREF="UserModeLinux-HOWTO.html#toc1.2">Why Would I Want User Mode Linux?</A>
</H2>
<P>
<OL>
<LI> If User Mode Linux crashes, your host kernel is still fine.</LI>
<LI> You can run a usermode kernel as a non-root user.</LI>
<LI> You can debug the User Mode Linux like any normal process.</LI>
<LI> You can run gprof (profiling) and gcov (coverage testing).</LI>
<LI> You can play with your kernel without breaking things.</LI>
<LI> You can use it as a sandbox for testing new apps.</LI>
<LI> You can try new development kernels safely.</LI>
<LI> You can run different distributions simultaneously.</LI>
<LI> It's extremely fun.</LI>
</OL>
</P>
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