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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 file systems 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:
49 The stage-1 bootstrap, typically PXE built into your Ethernet
50 card, loads a second-stage boot program.
52 The second-stage boot program, typically
55 the kernel, and boots the kernel.
59 mounts the root directory and continues from there.
62 Each of these phases are described in further detail below.
64 First, the stage-1 bootstrap loads the stage-2 boot program over
66 The stage-1 bootstrap typically uses
70 to obtain the filename to load, then uses
73 This file is typically called
75 and should be copied from
79 directory on the server, which is typically
82 The stage-2 boot program then loads additional modules and the kernel.
83 These files may not exist on the
92 configurations to specify the server holding
93 the second stage boot files and kernel.
94 The stage-2 program uses
98 to obtain these files.
104 you can install a version that uses
107 .Li LOADER_TFTP_SUPPORT=YES
110 then recompiling and reinstalling
112 via the command listed below.
113 It is often necessary to use
115 here so you can place a custom kernel
120 and do not have a custom root file system for the
122 client, the stage-2 boot will load your server's kernel as the kernel for
125 machine, which may not be what you want to have happen.
126 .Bd -literal -offset indent
128 make clean; make; make install
129 cp /boot/pxeboot /tftpdir/
132 In phase 3, the kernel acquires IP networking configuration in one
133 of two ways, and then proceeds to mount the root file system and start
135 If the phase 2 loader supports passing network configuration to the
136 kernel using the kernel environment, then the kernel will configure
137 the network interface using that information.
138 Otherwise, it must use
143 configuration information.
149 .Pa /etc/rc.d/resolv ,
153 .Pa /etc/rc.initdiskless .
157 client, you need the following:
162 server which exports a root and
164 partitions with appropriate permissions.
167 scripts work with read-only partitions, as long as root is exported with
169 so that some system files can be accessed.
172 can contain the following lines:
173 .Bd -literal -offset indent
174 <ROOT> -ro -maproot=0 -alldirs <list of diskless clients>
175 /usr -ro -alldirs <list of diskless clients>
180 is the mount point on the server of the root partition.
182 .Pa /usr/share/examples/diskless/clone_root
183 can be used to create a shared read-only root partition,
184 but in many cases you may decide to export
185 (again as read-only) the root directory used by
198 .Pa /etc/inetd.conf .
201 can be the following:
202 .Bd -literal -offset indent
204 hn:ht=1:vm=rfc1048:\\
208 :rp="<SERVER>:<ROOT>":
210 <CLIENT>:ha=0123456789ab:tc=.default
218 have the obvious meanings.
220 A properly initialized root partition.
222 .Pa /usr/share/examples/diskless/clone_root
223 can help in creating it, using the server's root partition
225 If you are just starting out, you should
226 simply use the server's own root directory,
228 and not try to clone it.
230 You often do not want to use the same
236 boot as you do on the server.
240 scripts provide a mechanism through which you can override various files
243 (as well as other subdirectories of root).
245 One difference that you should pay particular attention to is
249 .Pa /etc/defaults/rc.conf .
250 A typical value for a
253 .Va mountcritremote ,
254 however your needs may be different.
256 The scripts provide four
257 overriding directories situated in
260 .Pa /conf/<broadcast-ip> ,
262 .Pa /conf/<machine-ip> .
263 You should always create
265 which will entirely replace the server's
270 You can clone the server's
272 here or you can create a special file which tells the
275 to remount the server's
279 You do this by creating the file
280 .Pa /conf/base/etc/diskless_remount
281 containing the mount point to use as a basis of the
285 For example, the file might contain:
289 Alternatively, if the server contains several independent roots, the file
292 .Dl 10.0.0.1:/usr/diskless/4.7-RELEASE/etc
294 This would work, but if you copied
295 .Pa /usr/diskless/4.7-RELEASE
297 .Pa /usr/diskless/4.8-RELEASE
298 and upgraded the installation, you would need to modify the
300 files to reflect that move.
301 To avoid that, paths in
305 have the actual path of the client's root prepended to them so the file
306 could instead contain:
312 scripts create memory file systems to hold the overridden
314 Only a 5MB partition is created by default, which may not
315 be sufficient for your purposes.
316 To override this, you can create the
318 .Pa /conf/base/etc/md_size
319 containing the size, in 512 byte sectors, of the memory disk to create
322 You then typically provide file-by-file overrides in the
323 .Pa /conf/default/etc
325 At a minimum, you must provide overrides for
326 .Pa /etc/fstab , /etc/rc.conf ,
330 .Pa /conf/default/etc/fstab , /conf/default/etc/rc.conf ,
332 .Pa /conf/default/etc/rc.local .
334 Overrides are hierarchical.
335 You can supply network-specific defaults
337 .Pa /conf/ Ns Ao Ar BROADCASTIP Ac Ns Pa /etc
340 represents the broadcast IP address of
343 system as given to it via
349 features work in any of these directories.
350 The configuration feature works on directories other then
352 you simply create the directory you wish to replace or override in
353 .Pa /conf/{base,default,<broadcast>,<ip>}/*
354 and work it in the same way that you work
357 Since you normally clone the server's
360 .Pa /conf/base/etc/diskless_remount ,
361 you might wish to remove unneeded files from the memory file system.
363 if the server has a firewall but you do not, you might wish
366 You can do this by creating a
367 .Pa /conf/base/ Ns Ao Ar DIRECTORY Ac Ns Pa .remove
370 .Pa /conf/base/etc.remove ,
371 which contains a list of relative paths that the boot scripts should remove
372 from the memory file systems.
374 As a minimum, you normally need to have the following in
375 .Pa /conf/default/etc/fstab
376 .Bd -literal -offset indent
377 <SERVER>:<ROOT> / nfs ro 0 0
378 <SERVER>:/usr /usr nfs ro 0 0
381 You also need to create a customized version of
382 .Pa /conf/default/etc/rc.conf
384 the startup options for the
387 .Pa /conf/default/etc/rc.local
388 which could be empty but prevents the server's own
390 from leaking onto the
397 you will not need to set
401 because these will be already set by the startup code.
402 Finally, it might be convenient to use a
406 as the switch variable to do machine-specific configuration
409 clients share the same configuration
414 clients, which will be loaded using
418 must include support for the NFS client:
420 .D1 Cd "options NFSCL"
421 .D1 Cd "options NFS_ROOT"
423 If you are using a boot mechanism that does not pass network configuration
424 to the kernel using the kernel environment, you will also need to include
425 the following options:
427 .D1 Cd "options BOOTP"
428 .D1 Cd "options BOOTP_NFSROOT"
429 .D1 Cd "options BOOTP_COMPAT"
432 the PXE environment does not require these options.
436 booting environment relies on memory-backed file systems to
437 support temporary local storage in the event that the root file system
438 is mounted read-only; as such, it is necessary to add the following
439 to the device section of the kernel configuration:
443 If you use the firewall, remember to default to
446 will not be able to send/receive the
451 Be warned that using unencrypted
453 to mount root and user
454 partitions may expose information such as
467 .Pa ports/net/etherboot
471 environment first appeared in
474 This manpage is probably incomplete.
477 sometimes requires to write onto
478 the root partition, so the startup scripts mount MFS
479 file systems on some locations (e.g.\&
484 trying to preserve the original content.
485 The process might not handle all cases.