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NAME
reboot - bootstrapping procedures
SYNOPSIS
/etc/reboot [ -s ] [ -n ] [ -a ] [ -d ]
/etc/halt [ -n ]
DESCRIPTION
UNIX is started by placing it in memory at location zero and
transferring to zero. Since the system is not reenterable,
it is necessary to read it in from disk each time it is to
be bootstrapped.
Rebooting a running system
The preferred way to reboot is to log in on the console,
invoke kill 1 to take the system to single user, unmount
filesystems with /etc/umount -a and halt and restart the
system as described below under Console boots.
If access to the console is difficult, /etc/reboot may be
used to restart a running system. It normally syncs the
disks (see sync(8)), then causes a system boot and an auto-
matic disk check. If all this succeeds, the system is
brought up multi-user.
The options to reboot are:
-s Come up single-user after the reboot, without checking
the disks.
-n Don't sync the disks before performing the reboot.
-a Ask on the console for the name of the file to be
booted.
-d Write a crash dump to the swap area before rebooting.
/etc/halt syncs the disks and stops the CPU. If the -n
option is enabled, the disk sync is not performed.
Power fail and crash recovery
The system will normally reboot itself at power-up or after
crashes if the auto-restart is enabled on the machine front
panel. An automatic consistency check of the file systems
is performed. Unless this fails the system will resume
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multi-user operations.
Console boots: VAX-11/750
Sync the disks if necessary and possible. To recover con-
trol of the console (normally it is running as an ordinary
Unix terminal), type a control-P. This will halt the CPU
and yield a `>>>' prompt from the VAX console subsystem
(sic). (Under undocumented conditions, this may fail. If
so, hit the white button on the front panel.) The command
>>> B
will cause a normal automatic reboot. Use
>>> B/3
to come up single-user. This also will prompt (with `:')
for the name of the file to boot. The format of the file
name is
disk(m, n)file
where disk is `ra' for UDA50 disks with 4KB filesystems,
`sa' for UDA50 disks with 1KB filesystems, `up' for UNIBUS
SMD disks, `hp' for Massbus SMD disks; m is the drive number
(usually 0); n is the file system number on the drive (usu-
ally 0); and file is the Unix name of the file on the disk.
If the root disk is curdled, the bootstrap program /boot can
be read from another disk, say RA drive 1, by
>>> B/3 DUA1
To the console subsystem, the RA's are called DU; the Emulex
disks are EM. Note that regardless how a system is boot-
strapped, it will use drive 0 for the root disk.
Console boots: VAX-11/780
To halt a 780, type control-P, then issue the command
>>> H
to halt the CPU.
Rebooting a 780 is like a 750 except for the format of the B
command.
>>> B
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initiates automatic reboot.
>>> B ANY
comes up single user. Replace `ANY' by `HPS' for hp disk
single user reboot, `RPS' for rp reboot, and `UPS' for ra
reboot.
Generating system core images
If the system crashes, it attempts to save a copy of its
physical memory to the swap area, to be copied to the file
system after reboot (see savecore(8)). To save a core image
for a hung system, type on the console (after control-P if
necessary):
>>> I
>>> S C00
This resets the bus and jumps to the start of the dumping
code. The system will reboot automatically.
Examining system core images
Savecore saves in the dump directory two files: the copy of
physical memory, called vmcore.n, and a copy of the kernel
binary unix.n, where n is a sequence counter. To recover a
stack traceback at the time of the crash, type
$ adb unix.n vmcore.n
$<crash
$c
Pi(9.1) can examine kernel core dumps.
FILES
/unix default Unix kernel binary
/boot system bootstrap
SEE ALSO
fsck(8), init(8), rc(8)
BUGS
Our homemade boot ROM for Emulex disks always boots from
drive 0, no matter what you tell it.