1 .\" Copyright (c) 1994 Gordon W. Ross, Theo de Raadt
2 .\" Updated by Luigi Rizzo
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27 .\" $FreeBSD: src/share/man/man8/diskless.8,v 1.6.2.9 2003/01/25 18:56:44 dillon Exp $
34 .Nd booting a system over the network
36 The ability to boot a machine over the network is useful for
40 machines, or as a temporary measure while repairing or
41 re-installing filesystems on a local disk.
42 This file provides a general description of the interactions between
43 a client and its server when a client is booting over the network.
45 When booting a system over the network, there are three
46 phases of interaction between client and server:
50 The stage-1 bootstrap loads a boot program, from
52 The boot program loads a kernel.
54 The kernel does NFS mounts for root.
57 Each of these phases are described in further detail below.
59 In phase 1, the stage-1 bootstrap code loads a boot program,
60 which is typically able to control the network card.
61 The boot program can be stored in the BIOS, in a BOOT ROM
62 located on the network card (PXE, etherboot, netboot),
63 or come from a disk unit (e.g. etherboot or netboot).
65 In phase 2, the boot program loads a kernel.
67 this phase depends on the design of the boot program.
68 Typically, the boot program uses the
72 protocol to get the client's IP address and other boot
73 information, including but not limited to
74 the IP addresses of the NFS server, router and nameserver,
75 and the name of the kernel to load.
76 Then the kernel is loaded, either directly using NFS
77 (as it is the case for etherboot and netboot),
78 or through an intermediate loader called pxeboot and
79 loaded using TFTP or NFS.
81 In phase 3, the kernel again uses DHCP or BOOTP to acquire
82 configuration information, and proceeds to mount the
83 root filesystem and start operation. The boot
84 scripts recognize a diskless startup and peform
86 .Pa /etc/rc.d/initdiskless
88 .Pa /etc/rc.d/diskless .
89 In older systems the scripts are located in
92 .Pa /etc/rc.diskless2 .
94 In order to run a diskless client, you need the following:
97 An NFS server which exports a root and /usr partition with
98 appropriate permissions.
100 scripts work with readonly partitions, as long as root is exported with
102 so that some system files can be accessed.
105 can contain the following lines:
106 .Bd -literal -offset indent
107 <ROOT> -ro -maproot=0 -alldirs <list of diskless clients>
108 /usr -ro -alldirs <list of diskless clients>
113 is the mountpoint on the server of the root partition.
115 .Pa /usr/share/examples/diskless/clone_root
116 can be used to create a shared readonly root partition,
117 but in many cases you may decide to export
118 (again as readonly) the root directory used by
131 .Pa /etc/inetd.conf .
134 can be the following:
135 .Bd -literal -offset indent
137 hn:ht=1:vm=rfc1048:\\
141 :rp="<SERVER>:<ROOT>":
143 <CLIENT>:ha=0123456789ab:tc=.default
151 have the obvious meanings.
153 A properly initialized root partition.
155 .Pa /usr/share/examples/diskless/clone_root
156 can help in creating it, using the server's root partition
157 as a reference. If you are just starting out you should
158 simply use the server's own root directory,
160 and not try to clone it.
162 You often do not want to use the same
166 files for the diskless boot as you do on the server. The diskless boot
167 scripts provide a mechanism through which you can override various files
170 (as well as other subdirectories of root). The scripts provide four
171 overriding directories situated in
174 .Pa /conf/(broadcast-ip) ,
176 .Pa /conf/(machine-ip) .
177 You should always create
179 which will entirely replace the server's
181 on the diskless machine.
182 You can clone the server's
184 here or you can create a special file which tells the diskless boot scripts
185 to remount the server's
189 You do this by creating the file
190 .Pa /conf/base/etc/diskless_remount
191 containing the mount point to use as a basis of the diskless machine's
193 For example, the file might contain:
194 .Bd -literal -offset 4n
198 The diskless scripts create memory filesystems to hold the overriden
199 directories. Only a 2MB partition is created by default, which may not
200 be sufficient for your purposes. To override this you can create the
202 .Pa /conf/base/etc/md_size
203 containing the size, in 512 byte sectors, of the memory disk to create
206 You then typically provide file-by-file overrides in the
207 .Pa /conf/default/etc
208 directory. At a minimum you must provides overrides for
214 .Pa /conf/default/etc/fstab ,
215 .Pa /conf/default/etc/rc.conf ,
217 .Pa /conf/default/etc/rc.local .
219 Overrides are hierarchical. You can supply network-specific defaults
221 .Pa /conf/<BROADCASTIP>/etc
222 directory, where <BROADCASTIP> represents the broadcast IP address of
223 the diskless system as given to it via
229 features work in any of these directories.
230 The configuration feature works on directories other then
232 you simply create the directory you wish to replace or override in
233 .Pa /conf/{base,default,<broadcast>,<ip>}/*
234 and work it in the same way that you work
237 As a minimum, you normally need to have the following in
238 .Pa /conf/default/etc/fstab
239 .Bd -literal -offset indent
240 <SERVER>:<ROOT> / nfs ro 0 0
241 <SERVER>:/usr /usr nfs ro 0 0
242 proc /proc procfs rw 0 0
245 You also need to create a customized version of
246 .Pa /conf/default/etc/rc.conf
248 the startup options for the diskless client, and
249 .Pa /conf/default/etc/rc.local
250 which could be empty but prevents the server's own
252 from leaking onto the diskless system.
257 you will not need to set
261 because these will be already set by the startup code.
262 Finally, it might be convenient to use a
266 as the switch variable to do machine-specific configuration
267 in case a number of diskless clients share the same configuration
270 The kernel for the diskless clients, which will be loaded using
271 NFS or TFTP, should be built with at least the following options:
272 .Bd -literal -offset indent
275 options BOOTP_NFSROOT
279 If you use the firewall, remember to default to open or your kernel
280 will not be able to send/receive the bootp packets.
283 Be warned that using unencrypted NFS to mount root and user
284 partitions may expose information such as
287 This manpage is probably incomplete.
290 sometimes requires to write onto
291 the root partition, so the startup scripts mount MFS
292 filesystems on some locations (e.g.\&
297 trying to preserve the original content.
298 The process might not handle all cases.
308 .Xr ports/net/etherboot