All rights reserved.
This code is derived from software written and contributed
to Berkeley by William Jolitz.
%sccs.include.redist.man%
@(#)boot_i386.8 1.1 (Berkeley) 02/09/91
UNIX, an ordinary executable file, is placed into memory by bootstrap at location absolute zero, and entered at the executable's entry point (a_entry). Upon startup, the system reorganizes memory to suit the needs of the hardware configuration found, thus it is not designed to be restartable without being reloaded on reboot. Each time it is to be bootstrapped, it must be reloaded, usually from a disk file.
Rebooting a running system. When a UNIX is running and a reboot is desired, shutdown (8) is normally used. If there are no users then reboot can be used. Reboot causes the disks to be synced and allows the system to perform other shutdown activities such as resynchronizing hardware time-of-day clocks. A multi-user reboot (as described below) is then initiated. This causes a system to be booted and an automatic disk check to be performed. If all this succeeds without incident, the system is then brought up for many users.
Options to reboot are:
-n option avoids the sync. It can be used if a disk or the processor is on fire.
-q reboots quickly and ungracefully, without shutting down running processes first.
Reboot normally logs the reboot using syslog (8) and places a shutdown record in the login accounting file /var/log/wtmp. These actions are inhibited if the -n or -q options are present.
"Power fail and crash recovery." Normally, the system will reboot itself at power-up or after crashes. An automatic consistency check of the file systems will be performed as described in fsck (8). and unless this fails, the system will resume multi-user operations.
Cold starts. The 386 PC AT clones attempt to boot the floppy disk drive A (otherwise known as drive 0) first, and failing that, attempt to boot the hard disk C (otherwise known as hard disk controller 1, drive 0). The automatic boot will attempt to load vmunix from partition A of either the floppy or the hard disk. This boot may be aborted by typing any character on the keyboard repeatedly (four or five times at least) during the operating system load phase, after which the bootstrap will prompt for the file that you wish to load instead.
One exception to this is the 'd' key, which will not abort the load but instead silently force the DEBUG boot flags. The boot flags for an autoboot are 0, and 3 for the successive boot after an aborted autoboot sequence. No other provison is made for setting boot flags (yet). A specific device or bootstrap file may be used; for example,
The file specifications used for the boostrap when loaded with the \*(lqaskme\*(rq flag (e.g. an aborted autoboot) are of the form: device unit partition:where device is the type of the device, assumed to be on the ISA bus, to be searched, unit is the unit number of the disk or tape, and partition is the disk partition or tape file number. Normal line editing characters can be used when typing the file specification. The following list of supported devices may vary from installation to installation:
wd ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike controller fd 5 1/4" or 3 1/2" High density floppies
For example, to boot from a file system which starts at cylinder 0 of unit 0 of an IDE disk, type \*(lqwd0a:vmunix\*(rq to the boot prompt; \*(lqfd0a:vmunix\*(rq would specify a 3 1/2" floppy drive 0 .
In an emergency, the bootstrap methods described in the paper ``Installing and Operating 4.3BSD-Reno UNIX on the AT/386'' can be used to boot from a distribution tape.
/boot system bootstrap