Diskless Linux Mini Howto
by Robert Nemkin buci@math.klte.hu
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 <bkis@cartan.math.klte.hu> for translating this document
to English.
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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
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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, 94004531@postoffice.csu.edu.au
� /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
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bootpd -s
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or by using inetd. In this case you need to edit:
� /etc/inetd.conf to remove the hashmark from the start of these
lines:
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# tftp dgram udp wait root /usr/sbin/in.tftpd tftpd /export
# bootps dgram udp wait root /usr/sbin/in.bootpd bootpd
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� insert or uncomment the following two lines in /etc/services:
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bootps 67/tcp # BOOTP server
tftp 69/udp # TFTP server
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� restart inetd by
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kill -HUP <process id of inetd>.
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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:
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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:
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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
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/export/linux/machine1/bin
/export/linux/machine1/sbin
/export/linux/machine1/lib
/export/linux/machine1/etc
/export/linux/machine1/var
/export/linux/machine1/usr
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After the changes you will have
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/export/linux/machine1/bin
/export/linux/machine1/sbin
/export/linux/machine1/lib
/export/linux/machine1/etc
/export/linux/machine1/var
/export/linux/usr
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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
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cd /export/linux
for x in machine2 machine3 ; do
mkdir $x; cd $x
(cd ../machine1; tar cf - *) | tar xvf -
done
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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--) :
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# 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
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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:
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mkdir -p /tftpboot/export/linux/machine1
cd /tftpboot/export/linux/machine1
cp /export/linux/machine1/<name of the kernel> .
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Then type the following:
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mkdir -p /tftpboot/export/linux/machine2
cd ../machine2
ln -s ../machine2/<name of the kernel>
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5.7. Final work
Finally, you must insert
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/sbin/mount nfs_server:/export/linux/usr /usr
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as the first line of
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/export/linux/<machinex>/etc/rc.d/rc.S
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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 buci@math.klte.hu Thank
you.