Diskless Linux Mini Howto
 by Robert Nemkin [email protected]
 v0.0.3, 12 September 1996

 This document describes how to set up a diskless Linux box and copy�
 righted by Robert Nemkin. Copyright policy is GPL.  I whish to thank
 to Bela Kis <[email protected]> for translating this document
 to English.
 ______________________________________________________________________

 Table of Contents


 1. Changes

 2. How to set up a diskless Linux box

 3. Related documents

 4. Hardware

 5. Fundamental ideas

    5.1 Setting up the PC
    5.2 Setting up a bootpd on the server
    5.3 Configure the bootpd on the server.
    5.4 Understanding tftp
    5.5 Setting up a minimal Linux configuration on the remote server.
    5.6 Configuring the tftp server
    5.7 Final work

 6. Memory and diskspace requirements; speed

 7. Possible errors

 8. Errors and possible further expansions of this document



 ______________________________________________________________________

 1.  Changes


 �  v0.0.3 12 Sep 1996: Some minor error fixes


 2.  How to set up a diskless Linux box

 This document is about setting up a diskless Linux box. Sometimes it
 might be necessary to run Linux on PC's which have neither hard disks
 nor floppy drives. If a network, another Unix system with bootp, tftp,
 an NFS server, and an eprom burner is available then it is possible to
 set up and operate Linux without hard/floppy disks.


 3.  Related documents


 �  NFS-root Mini Howto

 �  Linux NET-2/3-HOWTO by Terry Dawson, [email protected]

 �  /usr/src/linux/README about configuring and compiling new kernels


 4.  Hardware

 Whatever is described here was checked on the following configuration

 �  Sun-OS 4.1.3 as boot server

 �  Slackware 2.3 + Linux 1.2.8 + wd 8013 ethercard.

 �  Working Ethernet lan


 5.  Fundamental ideas

 The fundamental idea is as follows: the PC will get its IP address
 from the boot server via the bootp protocol, using 0.0.0.0 as the
 initial IP address and its kernel via the tftp protocol.  (-- Booting
 across segments (via router) not a simple question, so either put both
 the server and the diskless boxes on the same lan segment or configure
 an UDP helper address in your router to the address of the server.
 Refer to your router product manual for further info.--)

 For this follow the steps below.


 5.1.  Setting up the PC

 Get the nfsboot package (the package is available from your favourite
 linux mirror site in the /pub/Linux/system/Linux-boot directory). It
 contains a booteprom image for the wd8013 card which can be directly
 burned in.

 There are alternative ways to prepare the PC:

 �  if your machine is not quite diskless, then you may use the little
    DOS program, or

 �  the binary floppy image contained in the same package.  If you
    choose the latter option you must write the image onto a floppy by
    the dd command.

 These images contain a bootp and tftp client.  You need to prepare a
 linux kernel too, which contains the nfs-root option.

 �  If you are using the latest stable kernel, linux-1.2.13, then you
    need to patch the kernel with the patchfile included in the nfsboot
    package  (-- Refer to patch(1)--)

 �  If you try to use the latest, but unstable kernel from the
    linux-1.3.x series, then you have to configure in the nfs-root
    option.

    You may or may not configure block device (floppy or hard disk)
    support, but you must configure tcp/ip support, wd ethernet card
    support, nfs filesystem support. Then recompile the kernel as
    usual.



 5.2.  Setting up a bootpd on the server

 It can be found in package bootpd-2.4.tar.gz (which can be found on
 your favourite linux mirror site in the
 /pub/Linux/system/Network/boot.net directory). Get the package,
 compile and install it. If your other Unix box happens to be a
 Slackware Linux then you may skip this step for the standard
 distributions contain a bootpd. The daemon can be run either directly
 by issuing command


      ______________________________________________________________________
              bootpd -s
      ______________________________________________________________________




 or by using inetd. In this case you need to edit:

 �  /etc/inetd.conf to remove the hashmark from the start of these
    lines:



      ______________________________________________________________________
      # tftp   dgram   udp     wait    root    /usr/sbin/in.tftpd     tftpd /export
      # bootps dgram   udp     wait    root    /usr/sbin/in.bootpd    bootpd
      ______________________________________________________________________





 �  insert or uncomment the following two lines in /etc/services:



      ______________________________________________________________________
      bootps          67/tcp          # BOOTP server
      tftp            69/udp          # TFTP server
      ______________________________________________________________________





 �  restart inetd by



      ______________________________________________________________________
              kill -HUP <process id of inetd>.
      ______________________________________________________________________





 5.3.  Configure the bootpd on the server.

 First of all, bootpd have a config file called bootptab which usually
 resides in /etc. You must modify it by inserting the IP addresses of
 your gateway, dns server, and the ethernet address(es) of your
 diskless machine(s).  An example /etc/bootptab:









 ______________________________________________________________________

 global.prof:\
         :sm=255.255.255.0:\
         :ds=192.168.1.5:\
         :gw=192.168.1.19:\
         :ht=ethernet:\
         :bf=linux:
 machine1:hd=/export/root/machine1:tc=global.prof:ha=0000c0863d7a:ip=192.168.1.140:
 machine2:hd=/export/root/machine2:tc=global.prof:ha=0800110244e1:ip=192.168.1.141:
 machine3:hd=/export/root/machine3:tc=global.prof:ha=0800110244de:ip=192.168.1.142:
 ______________________________________________________________________




 global.prof is a general template for host entries, where

 �  sm field contains the subnet mask

 �  ds field contains the address of the Domain Name Server

 �  gw field contains the default gateway address

 �  ht field contains the lan media hardware type

 �  bf field contains the name of the boot file

 After this, every machine must have a line:

 �  the first field contains the host name,

 �  hd field contains the directory of the bootfile,

 �  the global template can be included with the tc field,

 �  ha field contains the hardvare address of the ethernet card,

 �  ip field contains the assigned ip address.



 5.4.  Understanding tftp

 TFTP (Trivial File Transfer Protocol) is a file transfer protocol,
 such as ftp, but it's much simpler to help coding it in EPROMs. TFTP
 can be used in two ways:

 �  simple tftp: means that the client can acces to your whole file
    system. It's simpler but it's a big security hole (anyone can get
    your password file via tftp).

 �  secure tftp: the tftp server uses a chroot.2 system call to change
    it's own root directory. Anything outside the new root directory
    will be completelly inaccessible. Because of the chroot dir becomes
    the new root dir, the hd filed in the bootptab must reflect the new
    situation. For example: when using insecure tftp, the hd field
    contains the full path to the boot directory:
    /export/root/machine1.  When using secure tftp whith /export as
    root dir, then /export becomes / and the hd field must be
    /root/machine1.

    Almost every Unix implementation contains tfpt server, probably you
    don't need to install your own one.


 5.5.  server.  Setting up a minimal Linux configuration on the remote

 This may contain packages a, ap, n, and x of the Slackware
 distribution. To install more is OK; however the above packages
 suffice for the purposes of a diskless X terminal. For the
 installation you need a working Linux system. Find some disk space on
 the remote machine and export it read-write. Mount the exported
 directory onto somewhere (e.g. /mnt) on the file system of the Linux
 box. Start Linux setup and change the root option in the setup from /
 to /mnt. Then setup the above packages as usual. If you want to run no
 more than one diskless Linux then no changes are needed. On the other
 hand, if you plan to use more than one diskless machine then the above
 setup will not work because some files and directories must be private
 to the machines. The problem can be bypassed by moving the /usr (it
 contains no private data) and then create a separate subdir for each
 diskless machine. For example, if /export/linux/machine1 were mounted
 to /mnt then the directory structure after the initial setup will look
 like


      ______________________________________________________________________
      /export/linux/machine1/bin
      /export/linux/machine1/sbin
      /export/linux/machine1/lib
      /export/linux/machine1/etc
      /export/linux/machine1/var
      /export/linux/machine1/usr
      ______________________________________________________________________




 After the changes you will have


      ______________________________________________________________________
      /export/linux/machine1/bin
      /export/linux/machine1/sbin
      /export/linux/machine1/lib
      /export/linux/machine1/etc
      /export/linux/machine1/var
      /export/linux/usr
      ______________________________________________________________________




 Now create the subdirectories for the other machines. Assume for now
 that your diskless machines are called machine1, machine2, machine3,
 etc.; then you may use the following bash script to setup the other
 directories


      ______________________________________________________________________

              cd /export/linux
              for x in machine2 machine3 ; do
                      mkdir $x; cd $x
                      (cd ../machine1; tar cf - *) | tar xvf -
              done
      ______________________________________________________________________





 Then do the following export:

 �  /export/linux/usr                       readonly for everyone.

 �  /export/liunx/machine1          only to machine1 with rw,root
    rights.

 �  /export/liunx/machine2          only to machine2 with rw,root
    rights.

 �  /export/liunx/machine3          only to machine3 with rw,root
    rights.

    as follows (-- the format of this example follows the SunOs 4.1.3
    exports file syntax--) :


      ______________________________________________________________________

      # This file is /etc/export
      # for remote linux X terminals by Buci
      # this line is only once
      /export/root/usr             -access=linuxnet
      # these lines once for every host
      /export/root/machine1       rw=machine1,root=machine1
      /export/root/machine2       rw=machine2,root=machine2
      /export/root/machine3       rw=machine3,root=machine3
      ______________________________________________________________________




 Don't forget to run exportfs -a.


 5.6.  Configuring the tftp server


 Now it is time to configure the tftp server. If you do not need secure
 tftp then everything is quite simple for your clients can be booted
 from the /export directory.

 If a secure tftp is used then you can either make a full /export/linux
 directory structure under /tftpboot (with a single real kernel and
 symbolic links for the other machines), or let the /export directory
 be the boot directory of the secure tftpd. Or, if you have a separate
 tftpboot directory then, similarly, you need only the original
 directory structure with a single kernel and symbolic links for the
 others. You can achieve this setup by typing the following:


      ______________________________________________________________________
            mkdir -p /tftpboot/export/linux/machine1
            cd /tftpboot/export/linux/machine1
            cp /export/linux/machine1/<name of the kernel> .
      ______________________________________________________________________




 Then type the following:





 ______________________________________________________________________
       mkdir -p /tftpboot/export/linux/machine2
       cd ../machine2
       ln -s ../machine2/<name of the kernel>
 ______________________________________________________________________





 5.7.  Final work


 Finally, you must insert


      ______________________________________________________________________
         /sbin/mount nfs_server:/export/linux/usr /usr
      ______________________________________________________________________




 as the first line of



      ______________________________________________________________________
         /export/linux/<machinex>/etc/rc.d/rc.S
      ______________________________________________________________________




 where <machinex> stands for machine1, machine2, etc.


 6.  Memory and diskspace requirements; speed

 . I tested this for only Slackware 2.3; for other
 distributions/versions the following numbers may vary.

 �  Diskspace: 28MB + 6.5MB/machine

 �  RAM: I am using X on 8 MB. For only 4MB swap is needed, I guess,
    which can be created -- separately for each machine -- in /tmp. Do
    not forget to run mkswap.

 �  Speed: I had no problems on a 486 DX2/66 with 8 Megs.


 7.  Possible errors



 �  I found a strange error: in the /dev subdirectory SunOS corrupted
    the device entries so I needed to rerun MAKEDEV by mounting the
    subdirectory onto a disk based Linux box.  (The reason was the
    differences between the linux nfs and the SunOs nfs: both use 32
    bit for the Major and Minor device number, but linux uses 16 bit
    wide fields for both, SunOs uses 14 bit wide field for Major and 18
    bit wide filed for Minor device number.)

 �  When the diskless linux gets booted, there is only one route
    included in the routing table to the tftp server, so you need to
    set up correct routing tables. You have two choices here:
 �  configure every rc.S for every machine by hand

 �  use a bootp client package and write a generalized setup script


 8.  Errors and possible further expansions of this document


 �  Correct citation of related documents.

 �  SunOs is BSD based. Need to include SVR4 (e.g. Solaris) based
    server configuration.

 �  Although Linux is quite similar to SunOs as bootp/tftp server, a
    linux based server example might be usefull.

 �  Update this document to the current etherboot package.

 �  Show the differences between the nfs root patched kernel version
    1.2.13 and the newest 1.3.x kernel, which contains the nfs-root
    patch.

 �  Need to try other ethercards than wd8013

 �  Include configuration information for bootpc, a bootp client for
    linux to set up the correct rooting tables.

 �  Typos and other errors: please, report to [email protected] Thank
    you.

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