82 lines
3.7 KiB
HTML
82 lines
3.7 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9">
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<TITLE>NFS-Root mini-HOWTO: General Overview</TITLE>
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<LINK HREF="NFS-Root-3.html" REL=next>
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<LINK HREF="NFS-Root-1.html" REL=previous>
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<LINK HREF="NFS-Root.html#toc2" REL=contents>
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<BODY>
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<A HREF="NFS-Root-3.html">Next</A>
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<A HREF="NFS-Root-1.html">Previous</A>
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<A HREF="NFS-Root.html#toc2">Contents</A>
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<HR>
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<H2><A NAME="s2">2. General Overview</A></H2>
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<P>An NFS-mounted root filesystem is typically most useful in two situations:
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<UL>
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<LI>A system administrator may wish to aggregate storage for multiple
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workstations in order to simplify maintenance, improve security and
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reliability, and/or make more economical use of limited storage capacity.
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In this scenario, a single, large server may host a dozen or more
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workstations; all of the systems can be regularly backed up from a
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central location, and individual clients are less prone to damage
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by unsophisticated users or attack by malicious parties with physical
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access. (Of course, if the server itself is compromised, then so are
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all of the clients.)</LI>
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<LI>An embedded system may not have a disk, an IDE interface, or even
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a PCI bus. Even if it does, during development it may be too unstable
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to use the disk, and a ramdisk may be too small to include all of the
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necessary utilities or too large (as a part of the kernel image) to
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allow for rapid turnaround during testing and development. An NFS root
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allows quick kernel downloads, helps ensure filesystem integrity (since
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the server is basically impervious to crashes by the client), and provides
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virtually infinite storage.</LI>
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</UL>
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(In this document we'll use the terms <EM>client</EM> and <EM>workstation</EM>
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interchangeably.)
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<P>
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<P>However, there are two small problems from the client's perspective:
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<UL>
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<LI>It must find out its own IP address and possibly also the
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rest of the ethernet configuration (gateway, netmask, name servers, etc.).</LI>
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<LI>It must know or discover both the IP address of the NFS server and
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the mount path (on the server) to the exported root filesystem.</LI>
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</UL>
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<P>
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<P>The current implementation of <EM>NFSROOT</EM> in the Linux kernel (as of
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2.4.x) allows for several approaches, including:
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<UL>
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<LI>The complete ethernet configuration, including the <EM>NFS</EM>-path
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to be mounted, may be passed as parameters to the kernel via
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<B>LILO</B>, <B>LOADLIN</B>, or a hard-coded string within
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<CODE>linux/arch/i386/kernel/setup.c</CODE> (or its equivalent for other
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architectures).</LI>
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<LI>The IP address may be discovered by <EM>RARP</EM> and the <EM>NFS</EM>-path
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passed via kernel parameters.</LI>
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<LI>The IP address may be discovered by <EM>RARP</EM>, with the <EM>NFS</EM>-path
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derived from the <EM>RARP</EM> server and the just-granted IP address
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(loosely speaking, ``<CODE>mount -t nfs
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<<EM>RARP-server</EM>>:/tftpboot/<<EM>IP-address-of-client</EM>>/dev/nfs</CODE>'').</LI>
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<LI>The client configuration may be discovered by <EM>BOOTP</EM>.</LI>
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<LI>The client configuration may be discovered by <EM>DHCP</EM>.</LI>
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</UL>
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<P>Since the most common dynamic-address protocol these days is DHCP, its
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addition as an option in kernels 2.2.19 and 2.4.x (3 < x <= 14)
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is particularly welcome.
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<P>Before starting to set up a diskless environment, you should decide if
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you will be booting via <B>LILO</B>, <B>LOADLIN</B>, or a custom, embedded
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bootloader. The advantage of using something like <B>LILO</B> is flexibility;
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the disadvantage is speed--booting a Linux kernel without <B>LILO</B> is
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faster.
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This may or may not be a consideration.
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<P>
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<HR>
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<A HREF="NFS-Root-3.html">Next</A>
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<A HREF="NFS-Root-1.html">Previous</A>
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<A HREF="NFS-Root.html#toc2">Contents</A>
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