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1 .\" $NetBSD: boothowto.9,v 1.4 2009/09/11 19:44:03 wiz Exp $
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27 .Dd September 11, 2009
28 .Dt BOOTHOWTO 9
29 .Os
30 .Sh NAME
31 .Nm boothowto ,
32 .Nm BOOT_FLAG
33 .Nd flags passed to kernel during boot or shutdown
34 .Sh SYNOPSIS
35 .In sys/reboot.h
36 .In sys/systm.h
37 .Vt extern int boothowto;
38 .In sys/boot_flag.h
39 .Vt #define BOOT_FLAG(arg, retval) ...
40 .Sh DESCRIPTION
41 The
42 .Va boothowto
43 variable contains flags passed to the kernel by the boot loader (see
44 .Xr boot 8 ) ,
45 or the
46 .Xr reboot 2
47 system call.
48 The value is interpreted as a bit mask, with bits defined by the
49 .Dq Sy RB_ Ns No *
50 and
51 .Dq Sy AB_ Ns No *
52 symbols in
53 .In sys/reboot.h .
54 The value is made available via the
55 .Xr sysctl 7
56 variable
57 .Va kern.boothowto .
58 .Pp
59 The
60 .Dv BOOT_FLAG
61 macro defined in
62 .In sys/boot_flag.h
63 is used by many boot loaders to convert command line options into
64 .Va boothowto
65 flags.
66 Note that not all boot loaders use this macro, and some boot loaders
67 may have incompatible options.
68 .Pp
69 Where possible, flags set by the
70 .Xr reboot 2
71 system call will be passed to the new kernel after a reboot;
72 the extent to which this is possible is machine dependent.
73 .Pp
74 In the following tables,
75 each flag is listed with
76 its symbolic name,
77 the corresponding numeric value defined in
78 .In sys/reboot.h ,
79 and the option letter (if any) understood by the
80 .Dv BOOT_FLAG
81 macro.
82 .
83 .Ss Flags that affect booting or shutting down
84 The following flags affect actions taken during system boot
85 or shutdown.
86 .Bl -column RB_INITNAMEA 0x00000000 \&-x
87 .It Dv RB_AUTOBOOT Ta Li 0 Ta Ta
88 The default if no other flags are set.
89 Causes the system to boot in the normal way.
90 .It Dv RB_ASKNAME Ta Li 0x00000001 Ta Fl a Ta
91 This flag causes various parts of the system to prompt:
92 .Bl -bullet -compact
93 .It
94 The boot loader may prompt for the name or location of the
95 kernel to be booted.
96 .It
97 The kernel will prompt for the root file system device.
98 .It
99 The kernel will prompt for the root file system type.
100 .It
101 The kernel will prompt for the location of the dump device.
102 .It
103 The kernel will prompt for the path to the
104 .Xr init 8
105 program.
106 .El
107 Some subsystems set this flag when they are unable to automatically
108 make a decision.
109 .It Dv RB_SINGLE Ta Li 0x00000002 Ta Fl s Ta
110 Boot in single-user mode.
111 If this flag is set, the kernel passes the
112 .Fl s
113 option to
114 .Xr init 8 .
115 .It Dv RB_NOSYNC Ta Li 0x00000004 Ta Ta
116 If this flag is set, then some parts of the shutdown process will
117 be less graceful than usual:
118 .Bl -bullet -compact
119 .It
120 Disks will not be synced
121 (see
122 .Xr sync 2
123 and
124 .Xr cpu_reboot 9 ) .
125 .It
126 Devices will not be detached (see
127 .Xr autoconf 9 ) .
128 .\" actually, see config_detach_all, but that is undocumented
129 .It
130 File systems will not be unmounted (see
131 .Xr cpu_reboot 9 ,
132 and
133 .Xr vfs_shutdown 9 ) .
134 .It
135 The time of day clock will not be set (see
136 .Xr resettodr 9 ) .
137 .El
138 .It Dv RB_HALT Ta Li 0x00000008 Ta Fl b Ta
139 If this flag is set, then
140 .Xr reboot 2
141 will cause the system to halt instead of rebooting.
142 This flag may be set at boot time, and cannot be cleared by
143 .Xr reboot 2 .
144 .It Dv RB_INITNAME Ta Li 0x00000010 Ta Ta
145 This flag is obsolete.
146 It was previously used to cause the kernel to prompt for the name of the
147 .Xr init 8
148 program, but that function is now controlled by the
149 .Dv RB_ASKNAME
150 flag.
151 .It Dv RB_KDB Ta Li 0x00000040 Ta Fl d Ta
152 Gives control to a kernel debugger early in the boot sequence.
153 See
154 .Xr ddb 4 ,
155 .Dq "options KGDB"
156 in
157 .Xr options 4 ,
158 .\" the kgdb_* functions are undocumented
159 and
160 .Xr ipkdb 9 .
161 .It Dv RB_RDONLY Ta Li 0x00000080 Ta Ta
162 This flag is deprecated.
163 It previously caused the kernel to mount the root file system
164 in read-only mode, but now that is the default, and this flag
165 has no effect.
166 .It Dv RB_DUMP Ta Li 0x00000100 Ta Ta
167 Causes the kernel to dump memory to the dump device during shutdown.
168 See
169 .Xr savecore 8 ,
170 .Xr cpu_reboot 9 ,
171 and
172 .Xr dumpsys 9 .
173 .It Dv RB_MINIROOT Ta Li 0x00000200 Ta Fl m Ta
174 This flag informs the kernel that a mini-root file system is present
175 in memory.
176 See
177 .Xr md 4 ,
178 and
179 .Xr mdsetimage 8 .
180 .It Dv RB_STRING Ta Li 0x00000400 Ta Ta
181 This flag indicates that a boot string is present.
182 The string may be provided by
183 .Xr reboot 2
184 and will be passed to the boot loader if possible.
185 .It Dv RB_POWERDOWN Ta Li (RB_HALT|0x800) Ta Ta
186 This flag is used in conjunction with
187 .Dv RB_HALT .
188 If this flag is set, then then system will be powered down if possible.
189 If powerdown is not supported, then the system will halt.
190 .It Dv RB_USERCONF Ta Li 0x00001000 Ta Fl c Ta
191 This flag causes the kernel to invoke the
192 .Xr userconf 4
193 device configuration manager early in the boot sequence.
194 .El
195 .
196 .Ss Flags that affect verbosity
197 The following flags affect the verbosity of messages printed by the kernel.
198 These flags are used by several functions described in
199 .Xr kprintf 9
200 to control whether output is sent to the console, the system log,
201 .\" the /dev/log device driver is undocumented
202 both, or neither.
203 The use of flags that increase verbosity simultaneously with
204 the use of flags that decrease verbosity,
205 is not well defined.
206 .Bl -column RB_INITNAMEA 0x00000000 \&-x
207 .It Dv AB_NORMAL Ta Li 0 Ta Ta
208 The default, if none of the other
209 .Dv AB_*
210 flags is set, is that ordinary kernel messages are sent
211 both to the console and to the system log.
212 .It Dv AB_QUIET Ta Li 0x00010000 Ta Fl q Ta
213 Boot quietly.
214 Ordinary kernel messages are sent to the system log,
215 but not to the console.
216 Messages printed with
217 .Xr aprint_naive 9
218 are sent to the console, but not to the system log.
219 .It Dv AB_VERBOSE Ta Li 0x00020000 Ta Fl v Ta
220 Boot verbosely.
221 Some messages will be printed that would otherwise not be printed.
222 Both ordinary kernel messages, and messages printed with
223 .Xr aprint_verbose 9 ,
224 will be sent both to the console and to the system log.
225 If this flag is not set, then messages printed with
226 .Xr aprint_verbose 9
227 will be sent only to the system log.
228 .It Dv AB_SILENT Ta Li 0x00040000 Ta Fl z Ta
229 Boot silently.
230 Most kernel messages will be sent only to the system log, not to the console.
231 The
232 .Fn aprint_*
233 functions display a spinning symbol on the console.
234 .It Dv AB_DEBUG Ta Li 0x00080000 Ta Fl x Ta
235 Boot with debug messages.
236 .El
237 .
238 .Ss Machine-dependent flags
239 The following flags have machine-dependent meanings.
240 .Bl -column RB_INITNAMEA 0x00000000 \&-x
241 .It Dv RB_MD1 Ta Li 0x10000000 Ta Fl 1 Ta
242 Some ports use this flag to disable multiprocessor mode,
243 making them use only a single CPU.
244 The zaurus port uses this flag to enable the serial console.
245 .It Dv RB_MD2 Ta Li 0x20000000 Ta Fl 2 Ta
246 The i386 and amd64 ports use this flag to disable
247 .Xr acpi 4 .
248 .It Dv RB_MD3 Ta Li 0x40000000 Ta Fl 3 Ta
249 This flag is currently not used by any ports.
250 .It Dv RB_MD4 Ta Li 0x80000000 Ta Fl 4 Ta
251 This flag is currently not used by any ports.
252 .El
253 .
254 .Sh SEE ALSO
255 .\" sets boothowto
256 .Xr reboot 2 ,
257 .\" RB_KDB
258 .Xr ddb 4 ,
259 .\" RB_USERCONF
260 .Xr userconf 4 ,
261 .\" sysctl kern.boothowto
262 .Xr sysctl 7 ,
263 .\" sets boothowto
264 .Xr boot 8 ,
265 .\" .Xr crash 8 ,
266 .\" RB_SINGLE, RB_INITNAME
267 .Xr init 8 ,
268 .\" reboot/poweroff/halt calls reboot(2)
269 .Xr reboot 8 ,
270 .\" useful after RB_DUMP
271 .Xr savecore 8 ,
272 .\" RB_NOSYNC
273 .Xr sync 8 ,
274 .\" RB_NOSYNC, RB_HALT, RB_DUMP
275 .Xr cpu_reboot 9 ,
276 .\" aprint_*() functions use AB_* flags
277 .Xr kprintf 9
278 .Sh HISTORY
279 The
280 .Va boothowto
281 variable appeared in
282 .Bx 4.0 .
283 The
284 .Sy BOOT_FLAG
285 macro appeared in
286 .Nx 1.6 .
287 .Pp
288 The
289 .Dv RB_DFLTROOT
290 option is now
291 .Em obsolete .