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[blog.git] / posts / Abax / nfs_root.mdwn

[[!meta  title="Diskless Debian Etch"]]

Caveat: I have much more Linux experience than I had when I wrote this
HOWTO.  If I had to do it again, I'd probably use [[Gentoo]] instead
of [[Debian]], because I find it easier to write custom packages for
Gentoo.  Anyhow, here's my original HOWTO, preserved for posterity.


Overview
========

This HOWTO details the procedure I used to set up the abax cluster for
NFS-rooted network booting.  The system is useful in this case because
it centralizes the installation in the head node (server), which makes
maintaining, upgrading, or altering the computational nodes (clients)
easier.

This procedure follows mainly Tim Brom's [Microwulf configuration
notes][microwulf] with two major differences.

* Microwulf uses Ubuntu (gutsy?), and I'm using Debian etch.
* Microwulf has a seperate partition for each client's root, populated
  with an independent installation from CD.  I'm using a single
  partition for all of my clients, with the base system created using
  debootstrap (no CD).

For guidance in my deviations, I'm indebted to Bart Trojanowski's
[pxeboot and nfsroot notes][debian-nfsroot] and Falko Timme's notes on
[kernel compilation in Debian Etch][kernel].


Physical setup
==============

Our cluster has one server with eight clients.  The server has two
network cards, `eth0` and `eth1`.  `eth1` is connected to the outsize
world (WAN).  All of the clients have one network card, `eth0`.  All
of the `eth0`s are connected together through a gigabit switch (LAN).


Notation
========

Throughout this HOWTO, I will use `#` as the prompt for root, `$` as
the prompt for an unpriveledged user, and `chroot#` as the prompt for
a root in a `chroot`ed environment.  File contents will be listed with
the full path in the text introducing the listing.  For example,
`path/to/file`:

    Contents of file

All files are complete with the exception of lines containing `…`, in
which case the meaning of the example should be clear from the
context.


Basic server setup
==================

Installing the OS
-----------------

Boot the server with the Debian installation kernel following one of
the options in the [Debian installation guide][install].  I netbooted
my server from one of the client nodes following this procedure to set
up the DHCP and TFTP servers on the client and untarring
[netboot.tar.gz][] in my `tftpboot` directory.  After netbooting from
a client, don't forget to take that client down so you won't have
DHCP conflicts once you set up a DHCP server on your server.

Install Debian in whatever manner seems most appropriate to you.  I
partitioned my 160 GB drive manually according to

<table style="margin-left: auto; margin-right: auto">
  <tr><th>Mount point</th><th>Type</th><th>Size</th></tr>
  <tr><td>`/`        </td><td>ext3</td><td>280 MB</td></tr>
  <tr><td>`/usr`     </td><td>ext3</td><td>20 GB</td></tr>
  <tr><td>`/var`     </td><td>ext3</td><td>20 GB</td></tr>
  <tr><td>`/swap`    </td><td>swap</td><td>1 GB</td></tr>
  <tr><td>`/tmp`     </td><td>ext3</td><td>5 GB</td></tr>
  <tr><td>`/diskless`</td><td>ext3</td><td>20 GB</td></tr>
  <tr><td>`/home`    </td><td>ext3</td><td>93.7 GB</td></tr>
</table>

I went with a highly partitioned drive to ease mounting, since I will
be sharing some partitions with my clients.  To understand why
partitioning is useful, see the [Partition HOWTO][partition].

You can install whichever packages you like, but I went with just the
standard set (no Desktop, Server, etc.).  You can adjust your
installation later with any of (not an exhaustive list)

* [`tasksel`][tasksel], command line, coarse-grained package control.
* `apt-get`, command line, fine-grained package control.
* `aptitude`, curses frontend for `apt-get`.
* `synaptic`, gtk+ frontend for `apt-get`.
* `dpkg`, command line, package-management without dependency checking.

The base install is pretty bare, but I don't need a full blown
desktop, so I flesh out my system with:

    # apt-get install xserver-xorg fluxbox fluxconf iceweasel xterm xpdf
    # apt-get install build-essentials emacs21-nox

which gives me a bare-bones graphical system (fire it up with
`startx`) and a bunch of critical build tools (`make`, `gcc`, etc.).


Configuring networking
----------------------

We need to set up our server so that `eth1` assumes it's appropriate static IP on the WAN, and `eth0` assumes it's appropriate static IP on the LAN.
We achieve this by changing the default `/etc/network/interfaces` to

    # This file describes the network interfaces available on your system
    # and how to activate them. For more information, see interfaces(5).

    # The loopback network interface
    auto lo
    iface lo inet loopback

    allow-hotplug eth0           # start on boot & when plugged in
    iface eth0 inet static       # static LAN interface
        address 192.168.2.100
        netmask 255.255.255.0
        broadcast 192.168.2.255 

    allow-hotplug eth1           # start on boot & when plugged in
    #iface eth1 inet dhcp        # WAN DHCP interface (not used)
    iface eth1 inet static       # WAN static interface
        address XXX.XXX.YYY.YYY
        netmask 255.255.128.0
        broadcast XXX.XXX.127.255
        gateway XXX.XXX.ZZZ.ZZZ

where I've censored our external IPs for privacy.  The netmask selects
which addresses belong to which networks.  The way we've set it up,
all 192.168.2.xxx messages will be routed out `eth0`, and everything
else will go through `eth1` to it's gateway.  See the [Net-HOWTO][]
for more details.


Remote booting
==============

Server services
---------------

The clients will boot remotely using the Pre eXecution Environment
(PXE).  The boot procedure is

1. Client powers on.
2. Client BIOS comes up, detects attached devices, and looks for a
   DHCP server for advice on network booting.
3. DHCP server gives client an IP address, domain name, host name, the
   IP address of the TFTP server, and the location of the bootloader
   on the TFTP server.
4. Client gets bootloader from TFTP server.
5. BIOS hands over control to bootloader.
6. Bootloader gets kernel and initial ramdisk from TFTP server.
7. Bootloader hands over control to kernel
8. Kernel starts up the system, mounting root via NFS.
9. … after this point, it's just like a normal boot process.

We can see that we need to set up DHCP, TFTP, and NFS servers (not
necessarily on the same server, but they are in our case).

### pxelinux

The [pxe][] bootloader can be obtained with

    # apt-get install syslinux

which installs it to `/usr/lib/syslinux/pxelinux.0` along with a
manual and some other `syslinux` tools.

### DHCP

Install a server with

    # apt-get install dhcp

Configure the server with `/etc/dhcpd.conf`

    allow bootp;  # maybe?
    allow booting;# maybe?
    option domain-name "your.domain.com";
    option domain-name-servers XXX.XXX.XXX.XXX,YYY.YYY.YYY.YYY;

    subnet 192.168.2.0 netmask 255.255.255.0 {
        range 192.168.2.150 192.168.2.200; # non-static IP range
        option broadcast-address 192.168.2.255;
        option routers 192.168.2.100; # Gateway server
        next-server 192.168.2.100;    # TFTP server
        filename "pxelinux.0";        # bootloader

        host n1 {
                hardware ethernet ZZ:ZZ:ZZ:ZZ:ZZ:ZZ;
                fixed-address 192.168.2.101;
                option root-path "192.168.2.100:/diskless/n1";
                option host-name "n1";
        }
        … more hosts for other client nodes …
    }

This assigns the client a static hostname, domain name, and IP address
according to it's ethernet address (aka MAC address).  It also tells
all the clients to ask the TFTP server on 192.168.2.100 for the
bootloader `pxelinux.0`.  For extra fun, it tells the clients to send
packets to the router at 192.168.2.100 if they can't figure out where
they should go, and to use particular DNS servers to resolve domain
names to IP addresses.  This gives them access to the outside WAN.  I
don't know yet if the booting options are necessary, since I don't
know what they do.

We also need to ensure that the DHCP server only binds to `eth0`, since starting a DHCP server on your WAN will make you unpopular with your ISP.  You should have the following `/etc/default/dhcp`:

    INTERFACES="eth0"

Once the DHCP server is configured, you can start it with

    # /etc/init.d/dhcp restart

Check that the server is actually up with

    # ps -e | grep dhcp

and if it is not, look for error messages in

    # grep -i dhcp /var/log/syslog


### TFTP

There are several TFTP server packages.  We use `atftpd` here, but
`tftp-hpa` is also popular.  Install `atftpd` with

    # apt-get install atftpd xinetd

where `xinetd` is a super-server (replacing `inetd`, see `man xinetd`
for details).  Configure `atftpd` with `/etc/xinetd.d/atftpd`

    service tftp
    {
        disable     = no
        socket_type = dgram
        protocol    = udp
        wait        = yes
        user        = nobody
        server      = /usr/sbin/in.tftpd
        server_args = --tftpd-timeout 300 --retry-timeout 5 --bind-address 192.168.2.100 --mcast-port 1758 --mcast-addr 239.239.239.0-255 --mcast-ttl 1 --maxthread 100 --logfile /var/log/atftpd.log --verbose=10 /diskless/tftpboot
    }

Note that the `server_args` should all be on a single, long line,
since I haven't been able to discover if `xinetd` recognizes escaped
endlines yet.  This configuration tells `xinetd` to provide TFTP
services by running `in.tftpd` (the daemon form of `atftpd`) as user
`nobody`.  Most of the options we pass to `in.tftpd` involve
multicasting, which I believe is only used for MTFTP (which
`pxelinux.0` doesn't use).  `--logfile /var/log/atftpd.log
--verbose=10` logs lots of detail to `/var/log/atftpd.log` if it
exists.  You can create it with

    # touch /var/log/atftpd.log
    # chown nobody.nogroup /var/log/atftpd.log

The most important argument is `/diskless/tftpboot`, which specifies
the root of the TFTP-served filesystem (feel free to pick another
location if you would like).  This is where we'll put all the files
that the TFTP will be serving.  It needs to be read/writable by
`nobody`, so create it with

    # mkdir \tftpboot
    # chmod 777 tftpboot

(TODO: possibly set the sticky bit, remove writable?)

Finally, we need to restart the `xinetd` server so it notices the new
`atftpd` server.

    # /etc/init.d/xinetd restart

Check that the `xinetd` server is up with

    # ps -e | grep xinetd

and look for error messages with

    # grep -i dhcp /var/log/syslog

Just having `xinetd` up cleanly doesn't prove that `atftpd` is working
though, it just shows that the `atftpd` configuration file wasn't too
bungled.  To actually test `atftpd` we need to wait until the
[Synthesis Section][sec.synthesis] when we actually have files to
test-transfer.

### NFS

Install the NFS utilities on the server with

    # apt-get install nfs-common nfs-kernel-server

We go with the kernel server because we want fast NFS, since we'll be
doing a lot of it.  Set the NFS server up to export the root file
systems and the user's home directories with `/etc/exports`:

    /diskless/n1    192.168.2.0/24(rw,no_root_squash,sync,no_subtree_check)
    … other node root exports …
    /diskless       192.168.2.0/24(rw,no_root_squash,sync,no_subtree_check) # unnecessary
    /home           192.168.2.0/24(rw,no_root_squash,sync,no_subtree_check)
    /usr            192.168.2.0/24(rw,no_root_squash,sync,no_subtree_check)

Then let the NFS server know we've changed the `exports` file with

    # exportfs -av  # TODO: -r?

Test that the NFS server is working properly by `ssh`ing onto one of
the clients and running

    client# mkdir /mnt/n1
    client# mount 192.168.2.100:/diskless/n1 /mnt/n1
    client# ls /mnt/n1
    … some resonable contents …
    client# umount /mnt/n1
    client# rmdir /mnt/n1


Client setup
------------

The only client setup that actually happens on the client is changing
the BIOS boot order to preferentially boot from the network.  Consult
your motherboard manual for how to accomplish this.  It should be
simple once you get into the BIOS menu, which you generally do by
pressing `del`, `F2`, `F12`, or some such early in your boot process.
*Everything else happens on the server*.

### Root file system

We want to install a basic Debian setup on our clients.  Since each
client doesn't have it's own, private partition, we need to install
Debian using `debootstrap`.

    # apt-get install debootstrap
    # mkdir /diskless/n1
    # debootstrap --verbose --resolve-deps etch /diskless/n1
    # chroot /diskless/n1
    chroot# tasksel install standard
    chroot# dpkg-reconfigure locales
    chroot# apt-get install kernel-image-2.6-686 openssh-server nfs-client

TODO: what get's installed with standard?
See `/usr/share/tasksel/debian-tasks.desc` for a list of possible
tasks and [the debian docs][internals] for details on how a full
installation from CD or netboot.

We can also add a few utilities so we can work in our `chroot`ed environment

    chroot# apt-get install emacs21-nox

### Configuring `/etc`

The client will be getting its hostnames from the DHCP server, so
remove the default

    # rm /diskless/n1/etc/hostname

We also need to setup the `fstab` to mount `/home` and `/usr` from the
server.  In `/diskless/n1/etc/fstab`:

    # /etc/fstab: static file system information.
    #
    # <file system> <mount point>   <type>  <options>       <dump>  <pass>
    # automatically mount nfs root and proc through other means
    192.168.2.100:/home /home   nfs     defaults,nolock        0       0
    192.168.2.100:/usr /usr     nfs     defaults,nolock        0       0
    # we're diskess so we don't need to mount the hard disk sda :)
    #/dev/sda1       /               ext3    defaults,errors=remount-ro 0       1
    /dev/scd0       /media/cdrom0   udf,iso9660 user,noauto     0       0
    /dev/fd0        /media/floppy0  auto    rw,user,noauto  0       0


<a name="kernel" />

### Kernel and initial ramdisk

The kernel version number shows up often in this section.  You can
determine your kernel version number (in my case 2.6.18-6-686) with
`uname -r`.  Because kernel versions change fairly frequently, I'll
use `KERNEL_VERSION` to denote the kernel version string.

Your kernel must be compiled with NFS root support if it's going to have an [NFS root][nfsroot].
You can determine whether your kernel supports NFS roots with

    # grep 'ROOT_NFS' /diskless/n1/boot/config-KERNEL-VERSION

I didn't have it in my default debian etch 2.6.18-6-686 kernel, so I
had to recompile my kernel (see the [Kernel Appendix][app.kernel] and
[Falko's notes][kernel]).  My compiled kernel had a version string
`2.6.18-custom`.

Most kernels boot using an [initial ramdisk][initrd] (a compressed
root filesytem that lives in RAM).  This ramdisk contains the
necessary programs and scripts for booting the kernel.  We need to
create a ramdisk that can handle an NFS root, so `chroot` into your
client filesystem and install some tools

    chroot# apt-get install initramfs-tools 

Configure future ramdisks for NFS mounting with
`/etc/initramfs-tools/initramfs.conf`:

    # Configuration file for mkinitramfs(8). See initramfs.conf(5).
                …
    BOOT=nfs    # was BOOT=local
    …

Compile a new `initrd` with

    chroot# update-initramfs -u

If you compiled your own kernel as in [Kernel Appendix][app.kernel]
after setting up `initramfs.conf`, an appropriate ramdisk should have
been created automatically.

You can examine the contents of your ramdisk with

    $ cp /diskless/n1/boot/initrd.img-2.6.18-6-686 initrd.img.gz
    $ gunzip initrd.img.gz
    $ mkdir initrd
    $ cd initrd/
    $ cpio -i --make-directories < ../initrd.img 


<a name="synthesis" />

Synthesis
---------

To configure PXE, we need to bring `pxelinux.0` into our new
`tftpboot` directory

    # cp /usr/lib/syslinux/pxelinux.0 /diskless/tftpboot/

We also need to bring in our kernel image and initial ramdisk

    # cd /diskless/tftpboot
    # ln -s /diskless/n1/boot/initrd.img-2.6.18-custom
    # ln -s /diskless/n1/boot/vmlinuz-2.6.18-custom

`atftpd` handles the symbolic links, but if your TFTP server doesn't,
you'll have to copy the image and ramdisk over instead.

At this point you should test your TFTP server with test transfers.
Install the atftp client

    # apt-get install atftp

And attempt to transfer the important files.

    $ atftp 192.168.2.100
    tftp> status
    Connected:  192.168.2.100 port 69
    Mode:       octet
    Verbose:    off
    Trace:      off
    Options
     tsize:     disabled
     blksize:   disabled
     timeout:   disabled
     multicast: disabled
    mtftp variables
     client-port:   76
     mcast-ip:      0.0.0.0
     listen-delay:  2
     timeout-delay: 2
    Last command: quit
    tftp> get pxelinux.0
    tftp> get initrd.img-2.6.18-custom
    tftp> get vmlinuz-2.6.18-custom
    tftp> quit
    $ ls -l
    …
    -rw-r--r-- 1 sysadmin sysadmin 4297523 2008-05-30 09:27 initrd.img-2.6.18-custom
    -rw-r--r-- 1 sysadmin sysadmin   13480 2008-05-30 09:26 pxelinux.0
    -rw-r--r-- 1 sysadmin sysadmin 1423661 2008-05-30 09:27 vmlinuz-2.6.18-custom
    …

If this doesn't work, look for errors in `/var/log/syslog` and
`/var/log/atftpd.log` and double check your typing in the `atftpd`
configuration file.

The last stage is to configure the `pxelinux.0` bootloader.  Create a
configuration directory in `tftboot` with

    # mkdir /diskless/tftpboot/pxelinux.cfg

When each client loads `pxelinux.0` during the boot, they look for a
configuration file in `pxelinux.cfg`.  The loader runs through a
sequence of possible config file names, as described in
`pxelinux.doc`.  We'll have different rood directories for each of our
nodes, so we need a seperate config for each of them.  In order to
make our configs machine-specific, we'll use the ethernet (MAC)
address file-name scheme.  That is, for a machine with MAC address
AA:BB:CC:DD:EE:FF, we make the file
`pxelinux.cgf/01-aa-bb-cc-dd-ee-ff`.  TODO: base config on IP address.
In `/diskless/tftpboot/pxelinux.cfg/01-aa-bb-cc-dd-ee-ff`:

    default linux

    label linux
      kernel vmlinuz-2.6.18-custom
      append root=/dev/nfs initrd=initrd.img-2.6.18-custom
             nfsroot=192.168.2.100:/diskless/n1,tcp ip=dhcp rw

Note that the `append`ed args should all be on a single, long line,
since I haven't been able to discover if `pxelinux` recognizes escaped
endlines yet.  This file is basically like a `grub` or `lilo` config
file, and you can get fancy with a whole menu, but since this is a
cluster and not a computer lab, we don't need to worry about that.
Note that this file was only for our first node (`n1`).  You have to
make copies for each of your nodes, with the appropriate file names
and `nfsroot`s.

The kernel options are fairly self explanatory except for the `tcp`
for the `nfsroot` option, which says the client should mount the root
directory using TCP based NFS.  Traditional NFS uses UDP, which is
faster, but possibly less reliable for large files (like our kernel
and initrd).  However I'm having trouble tracking down a reliable
source for this.  For now, consider the `tcp` a voodoo incantation to
be attempted if the NFS booting isn't working.

You're done!  Plug a monitor into one of the clients and power her up.
Everything should boot smoothly off the server, without touching the
client's harddrive.


Adding clients
==============

To add a new client node `nX` to the cluster, we need to do the
following (which can be combined into an `add-client` script).  First,
we need to create a root directory for the new client

    # cd /diskless/
    # cp -rp n1 nX

Now we need to export that directory

    # echo '/diskless/nX        192.168.2.0/24(rw,no_root_squash,sync,no_subtree_check)' >> /etc/exports
    # exportfs -av

Finally, we need to set up the booting and DHCP options

    # cd /diskless/tftpboot
    # sed 's/\/diskless\/n1/\/diskless\/nX/' 01-xx-xx-xx-xx-xx-xx > 01-yy-yy-yy-yy-yy-yy
    # echo '    host n8 {
                hardware ethernet YY:YY:YY:YY:YY:YY;
                fixed-address 192.168.2.10X;
                option root-path "192.168.2.100:/diskless/nX/";
                option host-name "nX";
        }' >> /etc/dhcpd.conf
    # /etc/init.d/dhcp restart


Appendix
========

<a name="app.kernel" />

Compiling a kernel
------------------

See [Falko's notes][kernel] for an excellent introduction, and the
[NFS-root mini-HOWTO][nfsroot-mini] for NSF root particulars.

First, grab a bunch of useful compilation tools

    chroot# apt-get install wget bzip2 kernel-package
    chroot# apt-get install libncurses5-dev fakeroot build-essential initramfs-tools

Some of these (e.g. `wget`) should already be installed, but apt-get
will realize this, so don't worry about it.  Configure `initramfs` for
building NFS root-capable initial ramdisks by setting up
`/etc/initramfs-tools/initramfs.conf` as explained in the [Kernel
Section][sec.kernel].  For NSF root, your kernel needs the following
options:

    `IP_PNP_DHCP`
      Networking
        → Networking support (`NET [=y]`)
          → Networking options
            → TCP/IP networking (`INET [=y]`)
              → IP: kernel level autoconfiguration (`IP_PNP =y`)
    `ROOT_NFS` (`NET && NFS_FS=y && IP_PNP`)
      File systems
        → Network File Systems

I also used the build-in NFS client instead of the module.
Here is a `diff` of the original debian etch conf vs. mine:

    $ diff /diskless/n1/boot/config-2.6.18-6-686 .config
    4c4
    < # Sun Feb 10 22:04:18 2008
    ---
    > # Thu May 29 23:59:47 2008
    402c402,405
    < # CONFIG_IP_PNP is not set
    ---
    > CONFIG_IP_PNP=y
    > CONFIG_IP_PNP_DHCP=y
    > CONFIG_IP_PNP_BOOTP=y
    > CONFIG_IP_PNP_RARP=y
    3314c3317
    < CONFIG_NFS_FS=m
    ---
    > CONFIG_NFS_FS=y
    3325c3328,3329
    < CONFIG_LOCKD=m
    ---
    > CONFIG_ROOT_NFS=y
    > CONFIG_LOCKD=y
    3328c3332
    < CONFIG_NFS_ACL_SUPPORT=m
    ---
    > CONFIG_NFS_ACL_SUPPORT=y
    3330,3332c3334,3336
    < CONFIG_SUNRPC=m
    < CONFIG_SUNRPC_GSS=m
    < CONFIG_RPCSEC_GSS_KRB5=m
    ---
    > CONFIG_SUNRPC=y
    > CONFIG_SUNRPC_GSS=y
    > CONFIG_RPCSEC_GSS_KRB5=y
    3485c3489
    < CONFIG_CRYPTO_DES=m
    ---
    > CONFIG_CRYPTO_DES=y

Compile your shiny, new kernel with 

    chroot# make-kpkg clean
    chroot# fakeroot make-kpkg --initrd --append-to-version=-custom kernel_image kernel_headers

The new kernel packages are in the `src` directory

    chroot# cd /usr/src
    chroot# ls -l

Install the packages with

    chroot# dpkg -i linux-image-2.6.18-custom_2.6.18-custom-10.00.Custom_i386.deb


Troubleshooting
---------------

### No network devices available

Getting

    IP-Config: No network devices available.

messages during the boot (*after* the kernel is successfully loaded!).
According to [this post][no-net], the problem is due to a missing
kernel driver.

So I figured out what card I had:

    # lspci
    …
    03:03.0 Ethernet controller: Intel Corporation 82541GI/PI Gigabit Ethernet Controller
    03:04.0 Ethernet controller: Intel Corporation 82541GI/PI Gigabit Ethernet Controller
    …

The [ethernet HOWTO][ethernet] claimed that the `e1000` drivers were
required for Intel gigabit cards, and indeed I had the e1000 module
mounted on my server:

    # lsmod | less
    …
    e1000                 108480  0 
    …

I reconfigured my kernel with (old vs new):

    diff .config_mod_e1000 .config
    3,4c3,4
    < # Linux kernel version: 2.6.18-custom
    < # Fri May 30 00:13:47 2008
    ---
    > # Linux kernel version: 2.6.18
    > # Fri May 30 22:21:29 2008
    1542c1542
    < CONFIG_E1000=m
    ---
    > CONFIG_E1000=y

After which I recompiled and reinstalled the kernel as in the [Kernel
Appendix][app.kernel].

### Waiting for `/usr/`

On booting a client, I noticed a `Waiting for /usr/: FAILED` message
just before entering runlevel 2.  I attribute the error to a faulty
boot order on the client not mounting it's fstab filesystems before
trying to run something in `/usr/`.  There don't seem to be any
serious side effects though, since the wait times out, and by the time
I can log in to the node, `/usr/` is mounted as it should be.


[microwulf]: http://www.calvin.edu/~adams/research/microwulf/sys/microwulf_notes.pdf
[debian-nfsroot]: http://www.jukie.net/~bart/blog/nfsroot-on-debian
[kernel]: http://www.howtoforge.com/kernel_compilation_debian_etch
[install]: http://www.debian.org/releases/stable/installmanual
[netboot.tar.gz]: http://http.us.debian.org/debian/dists/etch/main/installer-i386/current/images/netboot/netboot.tar.gz
[partition]: http://www.tldp.org/HOWTO/text/Partition
[tasksel]: http://www.debian.org/releases/stable/i386/apds03.html.en
[net-howto]: http://www.faqs.org/docs/Linux-HOWTO/Net-HOWTO.html
[pxe]: http://syslinux.zytor.com/pxe.php
[internals]: http://d-i.alioth.debian.org/doc/internals/
[nfsroot]: http://www.kernel.org/doc/Documentation/filesystems/nfsroot.txt
[initrd]: http://www.ibm.com/developerworks/linux/library/l-initrd.html
[nfsroot-mini]: http://www.tldp.org/HOWTO/text/NFS-Root
[no-net]: http://www.linuxquestions.org/questions/linux-networking-3/ip-config-no-network-device-available-591273/
[ethernet]: http://tldp.org/HOWTO/Ethernet-HOWTO-4.html#ss4.24

[sec.kernel]: #kernel
[sec.synthesis]: #synthesis
[app.kernel]: #app.kernel