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NetBSD 6.1.5 - man page for boothowto (netbsd section 9)

BOOTHOWTO(9)			  BSD Kernel Developer's Manual 		     BOOTHOWTO(9)

     boothowto, BOOT_FLAG -- flags passed to kernel during boot or shutdown

     #include <sys/reboot.h>
     #include <sys/systm.h>

     extern int boothowto;

     #include <sys/boot_flag.h>

     #define BOOT_FLAG(arg, retval) ...

     The boothowto variable contains flags passed to the kernel by the boot loader (see boot(8)),
     or the reboot(2) system call.  The value is interpreted as a bit mask, with bits defined by
     the ``RB_*'' and ``AB_*'' symbols in <sys/reboot.h>.  The value is made available via the
     sysctl(7) variable kern.boothowto.

     The BOOT_FLAG macro defined in <sys/boot_flag.h> is used by many boot loaders to convert
     command line options into boothowto flags.  Note that not all boot loaders use this macro,
     and some boot loaders may have incompatible options.

     Where possible, flags set by the reboot(2) system call will be passed to the new kernel
     after a reboot; the extent to which this is possible is machine dependent.

     In the following tables, each flag is listed with its symbolic name, the corresponding
     numeric value defined in <sys/reboot.h>, and the option letter (if any) understood by the
     BOOT_FLAG macro.

   Flags that affect booting or shutting down
     The following flags affect actions taken during system boot or shutdown.

     RB_AUTOBOOT     0			 The default if no other flags are set.  Causes the sys-
					 tem to boot in the normal way.
     RB_ASKNAME      0x00000001    -a	 This flag causes various parts of the system to prompt:
					 o   The boot loader may prompt for the name or location
					     of the kernel to be booted.
					 o   The kernel will prompt for the root file system
					 o   The kernel will prompt for the root file system
					 o   The kernel will prompt for the location of the dump
					 o   The kernel will prompt for the path to the init(8)
					 Some subsystems set this flag when they are unable to
					 automatically make a decision.
     RB_SINGLE	     0x00000002    -s	 Boot in single-user mode.  If this flag is set, the ker-
					 nel passes the -s option to init(8).
     RB_NOSYNC	     0x00000004 	 If this flag is set, then some parts of the shutdown
					 process will be less graceful than usual:
					 o   Disks will not be synced (see sync(2) and
					 o   Devices will not be detached (see autoconf(9)).
					 o   File systems will not be unmounted (see
					     cpu_reboot(9), and vfs_shutdown(9)).
					 o   The time of day clock will not be set (see
     RB_HALT	     0x00000008    -b	 If this flag is set, then reboot(2) will cause the sys-
					 tem to halt instead of rebooting.  This flag may be set
					 at boot time, and cannot be cleared by reboot(2).
     RB_INITNAME     0x00000010 	 This flag is obsolete.  It was previously used to cause
					 the kernel to prompt for the name of the init(8) pro-
					 gram, but that function is now controlled by the
					 RB_ASKNAME flag.
     RB_KDB	     0x00000040    -d	 Gives control to a kernel debugger early in the boot
					 sequence.  See ddb(4), ``options KGDB'' in options(4),
					 and ipkdb(9).
     RB_RDONLY	     0x00000080 	 This flag is deprecated.  It previously caused the ker-
					 nel to mount the root file system in read-only mode, but
					 now that is the default, and this flag has no effect.
     RB_DUMP	     0x00000100 	 Causes the kernel to dump memory to the dump device dur-
					 ing shutdown.	See savecore(8), cpu_reboot(9), and
     RB_MINIROOT     0x00000200    -m	 This flag informs the kernel that a mini-root file sys-
					 tem is present in memory.  See md(4), and mdsetimage(8).
     RB_STRING	     0x00000400 	 This flag indicates that a boot string is present.  The
					 string may be provided by reboot(2) and will be passed
					 to the boot loader if possible.
     RB_POWERDOWN    (RB_HALT|0x800)	 This flag is used in conjunction with RB_HALT.  If this
					 flag is set, then then system will be powered down if
					 possible.  If powerdown is not supported, then the sys-
					 tem will halt.
     RB_USERCONF     0x00001000    -c	 This flag causes the kernel to invoke the userconf(4)
					 device configuration manager early in the boot sequence.

   Flags that affect verbosity
     The following flags affect the verbosity of messages printed by the kernel.  These flags are
     used by several functions described in kprintf(9) to control whether output is sent to the
     console, the system log, both, or neither.  The use of flags that increase verbosity simul-
     taneously with the use of flags that decrease verbosity, is not well defined.

     AB_NORMAL	     0			 The default, if none of the other AB_* flags is set, is
					 that ordinary kernel messages are sent both to the con-
					 sole and to the system log.
     AB_QUIET	     0x00010000    -q	 Boot quietly.	Ordinary kernel messages are sent to the
					 system log, but not to the console.  Messages printed
					 with aprint_naive(9) are sent to the console, but not to
					 the system log.
     AB_VERBOSE      0x00020000    -v	 Boot verbosely.  Some messages will be printed that
					 would otherwise not be printed.  Both ordinary kernel
					 messages, and messages printed with aprint_verbose(9),
					 will be sent both to the console and to the system log.
					 If this flag is not set, then messages printed with
					 aprint_verbose(9) will be sent only to the system log.
     AB_SILENT	     0x00040000    -z	 Boot silently.  Most kernel messages will be sent only
					 to the system log, not to the console.  The aprint_*()
					 functions display a spinning symbol on the console.
     AB_DEBUG	     0x00080000    -x	 Boot with debug messages.

   Machine-dependent flags
     The following flags have machine-dependent meanings.

     RB_MD1	     0x10000000    -1	 Some ports use this flag to disable multiprocessor mode,
					 making them use only a single CPU.  The zaurus port uses
					 this flag to enable the serial console.
     RB_MD2	     0x20000000    -2	 The i386 and amd64 ports use this flag to disable
     RB_MD3	     0x40000000    -3	 This flag is currently not used by any ports.
     RB_MD4	     0x80000000    -4	 This flag is currently not used by any ports.

     reboot(2), ddb(4), userconf(4), sysctl(7), boot(8), crash(8), init(8), reboot(8),
     savecore(8), sync(8), cpu_reboot(9), kprintf(9)

     The boothowto variable appeared in 4.0BSD.  The BOOT_FLAG macro appeared in NetBSD 1.6.

     The RB_DFLTROOT option is now obsolete.

BSD					September 11, 2009				      BSD

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