1 ==============================================
2 Mounting the root filesystem via NFS (nfsroot)
3 ==============================================
4
5 :Authors:
6 Written 1996 by Gero Kuhlmann <gero@gkm
7
8 Updated 1997 by Martin Mares <mj@atrey.
9
10 Updated 2006 by Nico Schottelius <nico-
11
12 Updated 2006 by Horms <horms@verge.net.
13
14 Updated 2018 by Chris Novakovic <chris@
15
16
17
18 In order to use a diskless system, such as an
19 example, it is necessary for the root filesyst
20 device. This may be an initramfs (see
21 Documentation/filesystems/ramfs-rootfs-initram
22 Documentation/admin-guide/initrd.rst) or a fil
23 following text describes on how to use NFS for
24 of this text 'client' means the diskless syste
25 server.
26
27
28
29
30 Enabling nfsroot capabilities
31 =============================
32
33 In order to use nfsroot, NFS client support ne
34 built-in during configuration. Once this has b
35 option will become available, which should als
36
37 In the networking options, kernel level autoco
38 along with the types of autoconfiguration to s
39 DHCP, BOOTP and RARP is safe.
40
41
42
43
44 Kernel command line
45 ===================
46
47 When the kernel has been loaded by a boot load
48 told what root fs device to use. And in the ca
49 both the server and the name of the directory
50 This can be established using the following ke
51
52
53 root=/dev/nfs
54 This is necessary to enable the pseudo-NFS-d
55 real device but just a synonym to tell the k
56 a real device.
57
58
59 nfsroot=[<server-ip>:]<root-dir>[,<nfs-options
60 If the `nfsroot' parameter is NOT given on t
61 the default ``"/tftpboot/%s"`` will be used.
62
63 <server-ip> Specifies the IP address of th
64 The default address is determi
65 (see below). This parameter al
66 servers for IP autoconfigurati
67
68 <root-dir> Name of the directory on the s
69 If there is a "%s" token in th
70 replaced by the ASCII-represen
71 IP address.
72
73 <nfs-options> Standard NFS options. All opti
74 The following defaults are use
75
76 port = as g
77 rsize = 4096
78 wsize = 4096
79 timeo = 7
80 retrans = 3
81 acregmin = 3
82 acregmax = 60
83 acdirmin = 30
84 acdirmax = 60
85 flags = hard
86
87
88 ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<
89 This parameter tells the kernel how to confi
90 and also how to set up the IP routing table.
91 nfsaddrs, but now the boot-time IP configura
92 NFS, so it was renamed to ip and the old nam
93 compatibility reasons.
94
95 If this parameter is missing from the kernel
96 assumed to be empty, and the defaults mentio
97 this means that the kernel tries to configur
98 autoconfiguration.
99
100 The <autoconf> parameter can appear alone as
101 parameter (without all the ':' characters be
102 "ip=off" or "ip=none", no autoconfiguration
103 autoconfiguration will take place. The most
104 is "ip=dhcp".
105
106 <client-ip> IP address of the client.
107 Default: Determined using aut
108
109 <server-ip> IP address of the NFS server.
110 If RARP is used to determine
111 the client address and this pa
112 replies from the specified ser
113
114 Only required for NFS root. Th
115 will not be triggered if it is
116 in operation.
117
118 Value is exported to /proc/net
119 (see below).
120
121 Default: Determined using auto
122 The address of the autoconfigu
123
124 <gw-ip> IP address of a gateway if the
125 Default: Determined using auto
126
127 <netmask> Netmask for local network inte
128 If unspecified the netmask is
129 assuming classful addressing.
130
131 Default: Determined using aut
132
133 <hostname> Name of the client.
134 If a '.' character is present,
135 before the first '.' is used a
136 after it is used as its NIS do
137 autoconfiguration, but its abs
138 If specified and DHCP is used,
139 domain name, if present) will
140 may cause a DNS record to be c
141
142 Default: Client IP address is
143
144 <device> Name of network device to use.
145 Default: If the host only has
146 Otherwise the device is determ
147 autoconfiguration. This is don
148 autoconfiguration requests out
149 and using the device that rece
150
151 <autoconf> Method to use for autoconfigur
152 In the case of options
153 which specify multiple autocon
154 requests are sent using all pr
155 to reply is used.
156
157 Only autoconfiguration protoco
158 into the kernel will be used,
159 this option::
160
161 off or none: don't use autoc
162 (do static IP
163 on or any: use any protoco
164 (default)
165 dhcp: use DHCP
166 bootp: use BOOTP
167 rarp: use RARP
168 both: use both BOOTP
169 (old option kep
170
171 if dhcp is used, the client id
172 format "ip=dhcp,client-id-type
173
174 Default: any
175
176 <dns0-ip> IP address of primary nameserv
177 Value is exported to /proc/net
178 (see below).
179
180 Default: None if not using aut
181 automatically if using autocon
182
183 <dns1-ip> IP address of secondary namese
184 See <dns0-ip>.
185
186 <ntp0-ip> IP address of a Network Time P
187 Value is exported to /proc/net
188 otherwise unused (see below).
189
190 Default: None if not using aut
191 automatically if using autocon
192
193 After configuration (whether manual or autom
194 are created in the following format; lines a
195 value is empty following configuration:
196
197 - /proc/net/pnp:
198
199 #PROTO: <DHCP|BOOTP|RARP|MANUAL>
200 domain <dns-domain>
201 nameserver <dns0-ip>
202 nameserver <dns1-ip>
203 nameserver <dns2-ip>
204 bootserver <server-ip>
205
206 - /proc/net/ipconfig/ntp_servers:
207
208 <ntp0-ip>
209 <ntp1-ip>
210 <ntp2-ip>
211
212 <dns-domain> and <dns2-ip> (in /proc/net/pnp
213 (in /proc/net/ipconfig/ntp_servers) are requ
214 they cannot be specified as part of the "ip=
215
216 Because the "domain" and "nameserver" option
217 resolvers, /etc/resolv.conf is often linked
218 that use an NFS root filesystem.
219
220 Note that the kernel will not synchronise th
221 servers it discovers; this is the responsibi
222 (e.g. an initrd/initramfs script that passes
223 /proc/net/ipconfig/ntp_servers to an NTP cli
224 root filesystem if it is on NFS).
225
226
227 nfsrootdebug
228 This parameter enables debugging messages to
229 log at boot time so that administrators can
230 NFS mount options, server address, and root
231 NFS client.
232
233
234 rdinit=<executable file>
235 To specify which file contains the program t
236 initialization, administrators can use this
237 The default value of this parameter is "/ini
238 file exists and the kernel can execute it, r
239 kernel command line parameters, including 'n
240
241 A description of the process of mounting the
242 found in Documentation/driver-api/early-user
243
244
245 Boot Loader
246 ===========
247
248 To get the kernel into memory different approa
249 They depend on various facilities being availa
250
251
252 - Booting from a floppy using syslinux
253
254 When building kernels, an easy way to
255 syslinux is to use the zdisk or bzdisk
256 and bzimage images respectively. Both
257 FDARGS parameter which can be used to
258
259 e.g::
260
261 make bzdisk FDARGS="root=/dev/nfs"
262
263 Note that the user running this comman
264 access to the floppy drive device, /de
265
266 For more information on syslinux, incl
267 for prebuilt kernels, see https://sysl
268
269 .. note::
270 Previously it was possible to
271 a floppy using dd, configure t
272 boot using the resulting flopp
273 method of booting.
274
275 - Booting from a cdrom using isolinux
276
277 When building kernels, an easy way to
278 uses isolinux is to use the isoimage t
279 image. Like zdisk and bzdisk, this tar
280 parameter which can be used to set the
281
282 e.g::
283
284 make isoimage FDARGS="root=/dev/nfs"
285
286 The resulting iso image will be arch/<
287 This can be written to a cdrom using a
288 cdrecord.
289
290 e.g::
291
292 cdrecord dev=ATAPI:1,0,0 arch/x86/bo
293
294 For more information on isolinux, incl
295 for prebuilt kernels, see https://sysl
296
297 - Using LILO
298
299 When using LILO all the necessary comm
300 specified using the 'append=' directiv
301 file.
302
303 However, to use the 'root=' directive
304 a dummy root device, which may be remo
305
306 e.g::
307
308 mknod /dev/boot255 c 0 255
309
310 For information on configuring LILO, p
311
312 - Using GRUB
313
314 When using GRUB, kernel parameter are
315 specification: kernel <kernel> <parame
316
317 - Using loadlin
318
319 loadlin may be used to boot Linux from
320 requiring a local hard disk to mount a
321 thoroughly tested by the authors of th
322 it should be possible configure the ke
323 to the configuration of LILO.
324
325 Please refer to the loadlin documentat
326
327 - Using a boot ROM
328
329 This is probably the most elegant way
330 With a boot ROM the kernel is loaded u
331 authors of this document are not aware
332 ROMs that support booting Linux over t
333 are two free implementations of a boot
334 etherboot, both of which are available
335 of which contain everything you need t
336
337 - Using pxelinux
338
339 Pxelinux may be used to boot linux usi
340 which is present on many modern networ
341
342 When using pxelinux, the kernel image
343 "kernel <relative-path-below /tftpboot
344 are passed to the kernel by adding the
345 It is common to use serial console in
346 see Documentation/admin-guide/serial-c
347
348 For more information on isolinux, incl
349 for prebuilt kernels, see https://sysl
350
351
352
353
354 Credits
355 =======
356
357 The nfsroot code in the kernel and the RARP
358 by Gero Kuhlmann <gero@gkminix.han.de>.
359
360 The rest of the IP layer autoconfiguration c
361 by Martin Mares <mj@atrey.karlin.mff.cuni.cz>
362
363 In order to write the initial version of nfs
364 Jens-Uwe Mager <jum@anubis.han.de> for his he
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