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@(#)boot_tahoe.8 6.2 (Berkeley) 10/29/88
UNIX is started by placing it in memory at location zero and transferring to the entry point. Since the system is not reenterable, it is necessary to read it in from disk or tape each time it is to be bootstrapped.
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 /etc/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 /usr/adm/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. These are processor-type dependent. On the CCI Power 6/32 and related processors, the system will do a standard autoboot from drive 0 upon power-up or reset. This automatic boot may be cancelled by typing a \*(lq#\*(rq in the first few seconds after reset. This enters console mode; the console prompt is \*(lq>\*(rq or \*(lq#>\*(rq. The boot flags can be set to any hexadecimal value n with the command
#> p23 n.The default device may be examined or set; see the Diagnostics and Debugging manual for the processor for details on device naming and syntax. After setting the boot flags and/or device, a bootstrap sequence can be initiated with
#> fbA specific device or bootstrap file may be used; for example,
#> fb xfd(1,0)would boot from the `a' partition on XFD drive 1.
The file specifications used for the boostrap when loaded with the \*(lqaskme\*(rq flag (register 23 set to 1 or 3) are of the form:
device(adaptor,controller,unit,minor)where device is the type of the device to be searched, adaptor is number of the VERSAbus (or VMEbus) to which the device is attached, controller is the unit number of the controller on that buss, unit is the unit number of the disk or tape, and minor is the disk partition or tape file number. Leading adaptor or controller numbers default to 0. Normal line editing characters can be used when typing the file specification. The following list of supported devices may vary from installation to installation:
dk SMD or ESDI disks on VDDC or SMD-E cy tape on Ciprico Tapemaster controller
For example, to boot from a file system which starts at cylinder 0 of unit 0 of an SMD-E disk, type \*(lqdk(0,0)vmunix\*(rq to the boot prompt; \*(lqdk(2,1,0)vmunix\*(rq would specify drive 1 on SMD-E controller 2.
In an emergency, the bootstrap methods described in the paper ``Installing and Operating 4.3BSD-tahoe UNIX on the Tahoe'' can be used to boot from a distribution tape.
/boot system bootstrap