FreeBSD/Linux Kernel Cross Reference
sys/boot/README
1 $FreeBSD: src/sys/boot/README,v 1.4 2005/01/05 22:16:10 imp Exp $
2
3 README file, for the boot config file setup. This is meant
4 to explain how to manage the loader configuration process.
5 The boot and loading process is either defined, or being
6 defined in boot(8) and loader(8).
7
8 The ongoing development of the FreeBSD bootloader, and its
9 rapid deployment while still in the development phase, has
10 resulted in a large number of installations with outdated
11 configurations. Those installations actively tracking the
12 FreeBSD development should also ensure that their bootloader
13 configurations are updated. If you see files discussed here
14 that your system doesn't yet have, add them yourself.
15
16 This is an effort to give the currently correct method for
17 setting up your boot process. It includes information on
18 setting up screen savers and plug and play information, and
19 also on recording any changes you make in your kernel
20 configuration. This file is temporary, because as I noted,
21 the process is still undergoing development, and will still
22 change. Man pages are coming out, but they're still going
23 to be somewhat fragile for a while. If you note anything in
24 here that's broken, it would be a good idea to report it to
25 the FreeBSD-current list, or to Daniel C. Sobral
26 <dcs@FreeBSD.org> or Mike Smith <msmith@FreeBSD.org>.
27
28 After the first two stages in the booting process (described
29 in boot(8)), the last stage of the booting process, called
30 the loader (see loader(8)) reads in the /boot/loader.rc
31 file. The two lines you should have there are:
32
33 include /boot/loader.4th
34 start
35
36 This reads the ficl (forth) initialization files, then
37 /boot/default/loader.conf. This file, which strongly
38 resembles in form /etc/rc.conf but functions quite
39 differently, has spots for endless user customization but
40 isn't yet completely finished. For one thing, it used to
41 assume a /kernel.config instead of a /boot/kernel.conf.
42 Watch the first few lines of /boot/defaults/loader.conf to
43 see if the file name changes.
44
45 [See the section at the end on loader.conf syntax]
46
47 You don't actually want to make any changes to
48 /boot/defaults/loader.conf, the file that is a hacking-
49 target is:
50
51 /boot/loader.conf
52
53 and might very likely not exist yet on your system). You
54 should copy /boot/defaults/loader.conf to /boot/loader.conf,
55 and then cut out anything you didn't want changed.
56
57 The start command also loads your kernel for you, so don't
58 put any lines in there like "load kernel", they'll fail (but
59 really have already worked for you). Start also reads in
60 the file /boot/defaults/loader.conf and /boot/loader.conf.
61 If you don't have /boot/loader.conf, you'll see a message on
62 boot about it, but it's a warning only, no other effects.
63 See the section on loader.conf syntax at the end of this
64 document, for some more pointers on loader.conf syntax.
65
66 The best way to manage splash screens is with entries in
67 /boot/loader.conf, and this is very clearly illustrated in
68 /boot/defaults/loader.conf (which you could just copy over
69 to /boot/loader.conf). I'm going to illustrate here how you
70 *could* do it in /boot/loader.rc (for information only)
71 but I don't recommend you do this; use the
72 /boot/defaults/loader.conf syntax, it's easier to get it
73 correct.
74
75 You can load your splash screen by putting the following
76 lines into /boot/loader.rc:
77
78 load splash_bmp
79 load -t splash_image_data /path/to/file.bmp
80
81 The top line causes the splash_bmp module to get loaded.
82 The second line has the parameter "-t" which tells the
83 loader that the class of DATA being loaded is not a module,
84 but instead a splash_image_data located in file
85 /path/to/file.bmp.
86
87 To get your plug and play data correctly set, run kget,
88 redirecting the output to /boot/kernel.conf. Note that kget
89 right now adds an extra "q" to it's output (from the q for
90 quit you press when you exit config), and if you want, you
91 can remove that from the file. Kget reports data only, so
92 feel free to run it, just to see the output. Make certain
93 you have the kernel option USERCONFIG set in your kernel, so
94 that you can do a boot -c, to initially set your cards up.
95 Then, edit /boot/loader.conf so that the following line
96 shows up (overwriting, in effect, a similar line in
97 /boot/default/loader.conf):
98
99 userconfig_script_load="YES"
100
101 My own pnp line looks like:
102 pnp 1 0 os irq0 15 irq1 0 drq0 1 drq1 0 port0 1332
103 (kget changes numbers from hexadecimal to decimal). Note
104 that, at this moment, the change from using /kernel.config
105 to using /boot/kernel.conf as the storage place for kernel
106 config changes is going on. Take a look at your
107 /boot/defaults/loader.conf, see what's defined as
108 userconfig_script_name, and if you override, make sure the
109 file exists. Note that the loader only has access to the
110 root filesystem, so be careful where you tell it to read
111 from.
112
113
114 o If you interrupt autoboot, you'll engage interactive
115 mode with loader. Everything you type will have the
116 same effects as if it were lines in /boot/loader.rc.
117
118 o While in interactive mode, you can get help by typing
119 "?", "help [<topic> [<subtopic>]]" and "help index".
120 These are mostly commands one would expect a normal
121 user to use. I recommend you play with them a little,
122 to gain further familiarity with what's going on.
123
124 Note that it is not possible to damage or corrupt your
125 system while experimenting with the loader, as it
126 cannot write to any of your filesystems.
127
128 o The command "unload" will unload everything. This is
129 very useful. Once loader.rc has finished and the
130 system is in the autoboot count-down, you will usually
131 have the kernel and other modules loaded. Now, suppose
132 your new /kernel is broken, how do you load
133 /kernel.old? By typing:
134
135 unload
136 load kernel.old
137 [any other modules you wish to load]
138 boot
139
140 o If you use loader.conf, you can do:
141
142 unload
143 set kernel=kernel.old
144 boot-conf
145
146 this will then load all the modules you have
147 configured, using kernel.old as kernel, and boot.
148
149 o From loader, you can use the command "more" to read the
150 contents of /boot/loader.rc, if you wish. This is not
151 FreeBSD's more. It is one of loader's builtin commands.
152 Useful if you can't quite recall what you have there.
153 :-) Of course, you can use this command to read
154 anything else you want.
155
156 o "boot -flag" works, "boot kernelname" works, "boot
157 -flag kernelname" doesn't. "boot kernelname -flag"
158 might work, but I'm not sure. The problem is that these
159 flags are kernel's flags, not boot's flags.
160
161 o There are a number of variables that can be set. You
162 can see them in loader.conf, but you can get much more
163 detailed information using the "help" command, eg. help
164 set <variablename>.
165
166 o The variable root_disk_unit is particularly important,
167 as it solves a relatively common problem. This problem
168 shows when the BIOS assign disk units in a different
169 way than the kernel. For example, if you have two IDE
170 disks, one on the primary, the other on the secondary
171 controller, and both as master, the default in most
172 kernels is having the first as wd0, and the second as
173 wd2. If your root partition is in wd2, you'll get an
174 error, because the BIOS sees these disks as 0 and 1
175 (well, 1 and 2), and that's what loader tells the
176 kernel. In this case, "set root_disk_unit=2" solves the
177 problem. You use this whenever the kernel fails to
178 mount to root partition because it has a wrong unit
179 number.
180
181 FILE OVERVIEW
182
183
184 o /boot/defaults/loader.conf -- Master configuration
185 file, not to be edited. Overridden by
186 /boot/loader.conf.
187
188 o /boot/loader.conf -- local system customization file,
189 in form very much like /boot/defaults/loader.conf.
190 This file is meant to be used by local users and the
191 sysinstall process.
192
193 o /boot/loader.conf.local -- local installation override
194 file. This is intended for use by installations with
195 large numbers of systems, to allow global policy
196 overrides. No FreeBSD tools should ever write this
197 file.
198
199 o /kernel.config -- old location of kernel configuration
200 changes (like pnp changes).
201
202 o /boot/kernel.conf -- new location for kernel
203 configuration changes.
204
205 o /boot/loader.rc -- loader initial configuration file,
206 chiefly used to source in a forth file, and start the
207 configuration process.
208
209 NOTES ON LOADER.CONF SYNTAX
210
211 I'm copy here from the last 11 lines from
212 /boot/defaults/loader.conf:
213
214 ##############################################################
215 ### Module loading syntax example ##########################
216 ##############################################################
217
218 #module_load="YES" # loads module "module"
219 #module_name="realname" # uses "realname" instead of "module"
220 #module_type="type" # passes "-t type" to load
221 #module_flags="flags" # passes "flags" to the module
222 #module_before="cmd" # executes "cmd" before loading module
223 #module_after="cmd" # executes "cmd" after loading module
224 #module_error="cmd" # executes "cmd" if load fails
225
226 The way this works, the command processor used by the loader
227 (which is a subset of forth) inspects these variables for
228 their suffix, and the 7 lines above illustrate all the
229 currently defined suffixes, and their use. Take the part
230 before the underscore, and customize it i(make it unique)
231 for your particular use, keeping the suffix to allow the
232 particular function you want to activate. Extra underscores
233 are fine, because it's only the sufixes that are scanned
234 for.
235
236
237
238 (authors Chuck Robey and Daniel Sobral).
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