boot(8) boot(8)
NAME
boot - bootstrap procedures
DESCRIPTION
Bootstrapping is the process of loading and executing a standalone
program. For the purpose of this discussion, bootstrapping means the
process of loading and executing the bootable operating system, but
any standalone program can be booted instead.
The bootstrap procedure on the Atari TT consists of the following
basic phases.
First, the machine is either turned on, or brought down to firmware
mode in any of a number of ways (hardware reset button, a shutdown or
init command, etc.). On powerup, the boot process is typically :
The TOS roms detect a bootable disk. The first sector of this disk is
loaded, then executed. This sector is called the rootsector.
The rootsector examines the ST partition table, also found in the
first sector, for a bootable ST partition. The first sector of this
ST partition is loaded and executed. This sector is called the
bootsector.
The bootsector obtains the disk's VTOC, locates the V_BOOT partition,
and loads and executes the unix bootstrap.
The bootstrap supports a standard device-file specification syntax of
the form:
device(controller,unit, slice)filename [options]
where
device
is a string specifying the device or driver name. Always hd.
controller and unit
specify the SCSI target and Logical Unit number to be used and
are passed to the kernel in the bootargs structure.
slice specifies the partition number,
filename
specifies the name of the file to be loaded, and
options
specifies an option string.
On startup, the boot displays the default specification. There is
then a pause during which the user may break in to interactive mode
by typing any character other than <CR>. Typing <CR> aborts the
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delay and causes the default file to be loaded immediately.
Once in interactive mode, the user may type in a device-file
specification. Any of the fields may be omitted, resulting in the
default values being used. When a value for any field is specified,
it becomes the new default. For example, if the file specified by
the filename field is not found, it is only necessary to type in
another filename to load that file from the same device. If only two
numeric arguments are supplied within the parentheses, they are
interpreted as controller and drive; if only one argument is
supplied, as controller. To specify drive or slice while leaving the
controller or drive as default, the leading commas must be typed.
The bootstrap recognizes two types of boot: an ``auto boot'' and a
``demand'' boot. In an auto boot, the EDT probe programs are run and
the date of the /stand/system file is checked. If there is a
mismatch between the devices supported by the kernel and those found
by probing, or if the system file has been changed, the file
/stand/mUNIX is loaded and the system will run cunix(1M) to rebuild
/stand/unix when it comes up. In a demand boot, no such checking is
performed.
If the initial kernel name is unix , an auto boot is performed;
otherwise, a demand boot. If interactive mode is entered, a demand
boot is assumed unless otherwise requested (see options below).
The following option flags are recognized in the options field of a
device-file specification:
-d force a demand boot - that is, do not reconfigure (this is the
default in interactive mode)
-m enter magic mode: the file is loaded but not executed
-n inhibit running of the EDT probe programs
-r request a reconfiguration, if flagged by the EDT probe process
or if the /stand/system file has been touched
-Dn set the level of debugging to n, a number in the range zero to
nine (0-9). The bootstrap starts in debug level zero - that
is, no debugging. Higher values cause the printing of
increasing amounts of detail. If n is omitted, a level of 1 is
assumed.
-R<device-file>
Specifies the root device that the kernel should use. Only the
hd
specification may be omitted. The kernel must be configured
with ROOTDEV set to NODEV for this option to have an effect.
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E.g. from a bootstrap loaded from disk 0, to load a kernel from
disk 3 lun 0 slice 3, with a root of disk 3, lun 0 and slice 1,
type:
hd(3,0,3)unix -R(3,0,1)
The bootable operating system file is /stand/unix. The /stand
partition is defined in the disk's VTOC table.
A copy of the rootsector is kept in /etc/T0boot.
A copy of the bootsector is kept in /etc/U0boot.
Both these bootstraps are installed using partinit(1m ).
A copy of the unix bootstrap is kept in /etc/v4boot. This is
installed on a new disk using newboot(1m ) .
SEE ALSO
init(1M), newboot(1M), partinit(1M), shutdown(1M), inittab(4),
vfstab(4).
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