V8/usr/man/man8/reboot.8

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.TH REBOOT 8
.SH NAME
reboot \- bootstrapping procedures
.SH SYNOPSIS
.B /etc/reboot
[
.B \-s
] [
.B \-n
] [
.B \-a
] [
.B \-d
]
.PP
.B /etc/halt
[
.B \-n
]
.SH DESCRIPTION
.PP
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.
.SS
.B Rebooting a running system
.PP
The preferred way to reboot is to log in on the console,
invoke
.B kill 1
to take the system to single user,
unmount filesystems with
.B /etc/umount \-a
and halt and restart the system
as described below under
.BR "Console boots" .
.PP
If access to the console is difficult,
.I /etc/reboot
may be used to
restart a running system.
It normally syncs the disks
(see
.IR sync (8)),
then causes a system
boot and an automatic disk check.  If all this succeeds,
the system is brought up multi-user.
.PP
The options to
.I reboot
are:
.TP
.B \-s
Come up single-user after the reboot, without checking the disks.
.TP
.B \-n
Don't sync the disks before performing the reboot.
.TP
.B \-a
Ask on the console for the name of the file to be booted.
.TP
.B \-d
Write a crash dump to the swap area
before rebooting.
.PP
.I /etc/halt
syncs the disks and stops the CPU.
If the
.B \-n
option is enabled, the disk sync is not performed.
.SS
.B Power fail and crash recovery
.PP
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 multi-user operations.
.SS
.B Console boots: VAX-11/750
.PP
Sync the disks if necessary and possible.
To recover control 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
.IP
>>> B
.PP
will cause a normal automatic reboot. Use
.IP
>>> B/3
.PP
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
.IP
disk(m, n)file
.PP
where
.I 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;
.I m
is the drive number (usually 0);
.I n
is the file system number on the drive (usually 0); and
.I file
is the Unix name of the file on the disk.
.PP
If the root disk is curdled, the bootstrap program
.I /boot
can be read from another
disk, say RA drive 1, by
.IP
>>> B/3 DUA1
.PP
To the console subsystem, the RA's are called DU;
the Emulex disks are EM.
Note that regardless how a system is bootstrapped, it will use drive 0 for the
root disk.
.SS
.B Console boots: VAX-11/780
.PP
To halt a 780,
type control-P,
then issue the command
.IP
>>> H
.PP
to halt the CPU.
.PP
Rebooting a 780 is like a 750 except for the format of the B command.
.IP
>>> B
.PP
initiates automatic reboot.
.IP
>>> B ANY
.PP
comes up single user.
Replace `ANY' by `HPS' for hp disk single user reboot, `RPS' for rp reboot,
and `UPS' for ra reboot.
.SS
.B Generating system core images
.PP
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
.IR savecore (8)).
To save a core image for a hung system, type on the console (after control-P
if necessary):
.nf
.IP
>>> I
>>> S C00
.fi
.PP
This resets the bus and jumps to the start of the dumping code.
The system will reboot automatically.
.SS
.B Examining system core images
.PP
.I Savecore
saves in the dump directory two files: the copy of physical memory, called
.IR vmcore.n ,
and a copy of the kernel binary
.IR unix.n ,
where
.I n
is a sequence counter.
To recover a stack traceback at the time of the crash, type
.nf
.IP
$ adb unix.\f2n\fP vmcore.\f2n\fP
$<crash
$c
.fi
.PP
.IR Pi (9.1)
can examine kernel core dumps.
.SH FILES
.ta \w'/usr/mdec/mboot   'u
/unix	default Unix kernel binary
.br
/boot	system bootstrap
.SH "SEE ALSO"
fsck(8), init(8), rc(8)
.SH BUGS
Our homemade boot ROM for Emulex disks
always boots from drive 0,
no matter what you tell it.