.TH BOOT 8
.SH NAME
boot \- connect to the root file server
.SH SYNOPSIS
.B /boot
[
.B -fkm
]
[
.BI -u username
]
[
.IB method ! fs-addr
]
.SH DESCRIPTION
.PP
.I Boot
is the first program run after a kernel has been loaded.
It connects to the file server that will serve the
root, performs any authentication needed to
connect to that server, and
.IR exec (2)'s
the
.IR init (8)
program.
It is started by the kernel, never run directly by the user.  See
.IR booting (8)
for information about the process of loading the kernel (and
.IR boot )
into memory.
.PP
Once loaded, the kernel initializes its data structures and devices.
It sets the two environment variables
.B /env/cputype
and 
.B /env/terminal
to describe the processor.
It then binds a place-holder file server,
.IR root (3),
onto 
.B /
and crafts an initial process whose sole function is to
.IR exec (2)
.BR /boot ,
a binary which is compiled into
.IR root (3).
.PP
The command line passed depends
on the information passed from boot ROM
to kernel.
On the MIPS Magnum and SGI Power Series
the command line passed to
.I boot
is the same as that given to the ROM monitor.
.PP
On AT&T Gnots the command line is
.IP
.B /68020/9gnot
.IB method ! server
.PP
On the Nextstation , no information is passed from
the boot ROM or program.  The command line is
.IP
.EX
.B /68020/9nextstation
.EE
.PP
On the PC, each line in the DOS file
.B plan9.ini
of the form
.IB name = value
is passed to the boot program as an environment
variable with the same name and value.
The command line is
.IP
.B /386/9pc
.IB method ! server
.PP
.I Boot
must determine the file server to use
and a method with which to connect to it.
It must also set a user name to be used
as the owner of devices and all console
processes and an encryption key to be used
when challenged.
.I Boot
will prompt for these.
.PP
Method and address are prompted for first.
The prompt lists all valid methods, with the default in brackets.
.IP
.EX
root is from (il, tcp, hs, local)[il]:
.EE
.PP
A newline picks the default.
Other possible responses are
.I method
or
.IB method ! address\f1.
To aid in automatic reboot, the default is automatically
taken on CPU servers if nothing is typed within 15 seconds.
.PP
The other interactions depend on whether the system
is a
terminal or a CPU server.
.SS Terminal
.PP
The terminal must have a
.I username
to set.
If none is specified with the
.B -u
option,
.I boot
will prompt for one on the console:
.IP
.EX
user: 
.EE
.PP
The user will also be prompted for a password to
be used as an encryption key on each
.IR attach (5):
.IP
.EX
password: 
.EE
.PP
With most
.I methods
.I boot
can now connect to the file server.
However, with the serial line
.I methods
.B 9600
and
.BR 19200 ,
the actual mechanics of setting up the complete connection
are too varied to put into the boot program.
Instead
.I boot
lets the user set up the connection.
It prints a prompt on the console and then simulates
a dumb terminal between the user and the serial line:
.IP
.EX
Connect to file system now, type ctrl-d when done.
(Use the view or down arrow key to send a break)
.EE
.PP
The user can now type at a modem or a Datakit
.B "destination please:"
interface to set up the connection to a TSM8 card.
At Murray Hill, a user would type
.B nj/astro/plan85
at this point.
When the user types a control-D,
.I boot
stops simulating a terminal and starts the file
system protocol over the serial line.
.PP
Once connected,
.I boot
mounts
the root file system before
.B /
and makes the connection available as
.B #s/boot
for subsequent processes to
.B mount
(see
.IR bind (2)).
.I Boot
completes by
.IR exec (2)'ing
.B /$objtype/init
.BR -t .
If the
.B -m
option is given it is also passed as an option to
.IR init .
.PP
If the kernel has been built with the cache file system,
.IR cfs (4),
the local disk partition
.B /dev/[sh]d[01]cache
exists, and the root file system is from a remote server,
then the kernel will insert a user level cache
process between the remote server and the local namespace
that caches all remote accesses on the local partition.
The
.B -f
flag commands
.B cfs
to reformat the cache partition.
.SS CPU Servers
.PP
The user owning devices and console processes on CPU servers
and that user's domain and encryption key are
read from NVRAM on all machines except PC's.
PC's keep the information in the disk partition
.BR /dev/[sh]d[01]nvram .
If a
.B -k
option is given or if no stored information is found
.I boot
will prompt for all three items and store them.
.IP
.EX
password: 
authid: bootes
authdom: research.att.com
.EE
.PP
The key is used for mutual authentication of the server and its clients.
The domain and id identify the owner of the key.
.PP
Once connected,
.I boot
behaves as on the terminal except for
.IR exec (2)'ing
.B /$objtype/init -c\f1.
.SS Booting Methods
.PP
The methods available to any system depend on what was
compiled into the kernel.
The complete list of booting methods are listed below.
.TP 8
.B cyc
connect via a point-to-point fiber link using Cyclone boards.
If specified, the address must be the number
of the Cyclone board to be used, default 0.
.TP 8
.B il
connect via Ethernet using the IL protocol.
.TP 8
.B tcp
connect via Ethernet using the TCP protocol.
This method is used only if the initial file server
is on a Unix system.
.TP 8
.B hs
connect via Datakit using the high speed Datakit
card.
.TP 8
.B incon
connect via Datakit using the Incon interface.
.TP 8
.B 9600
connect via Datakit using the serial interface
at 9600 baud.
.TP 8
.B 19200
connect via Datakit using the serial interface
at 19200 baud.
.TP 8
.B local
connect to the local file system.
.PP
For the
.B il
and 
.B tcp
methods,
the address must be a numeric IP address.
If no address is specified,
a file server address will be found from another
system on the network using the BOOTP protocol and
the Plan 9 vendor-specific fields.
For the Datakit methods,
.BR hs ,
.BR 9600 ,
.BR 19200 ,
and
.BR incon ,
the address must be specified and must
be a relative path name to the file server.
If no address is specified, the address
.B Nfs
is used.
.SH FILES
.B #s/boot
.SH SOURCE
.B /sys/src/9/boot
.SH "SEE ALSO"
.IR root (3),
.IR bootp (8),
.IR init (8)
