.TH BOOT 8
.SH NAME
boot \- connect to the root file server
.SH SYNOPSIS
.B /boot/boot
[
.B -fkm
]
[
.BI -u username
]
[
.IB method ! fs-addr
]
[
.I args
]
.SH DESCRIPTION
.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/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.
Machines that boot directly from ROM (that is, most machines other than PCs)
pass the boot line given to the ROM directly to
.IR boot .
.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 /386/9dos
.IB method ! server
.PP
(The first argument is ignored by
.IR boot .)
.I Boot
must determine the file
.I server
to use
and a
.I method
with which to connect to it.
Typically this will name a file server on the network,
or state that the root file system is on local disk and name the partition.
The complete list of methods is given below.
.PP
.I Boot
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, for example:
.IP
.EX
bootargs is (tcp, local!device)[/dev/sdC0/fscache]:
.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
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 the modem to
dial the number.  What is typed depends on
the modem and is beyond this discussion.
.PP
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 /$objtype/init
.BR -t .
If the
.B -m
option is given it is also passed as an option to
.IR init .
If the environment variable
.B init
is set (via
.IR plan9.ini (8)),
it is used as a command line to exec instead.
.PP
If the kernel has been built with the cache file system,
.IR cfs (4),
the local disk partition
.BI /dev/sd XX /cache
(where
.B XX
is a unit specifier)
exists, and the root file system is from a remote server,
then the kernel will insert a user level cache
process between the remote server and the local namespace
that caches all remote accesses on the local partition.
The
.B -f
flag commands
.B cfs
to reformat the cache partition.
.SS CPU Servers
The user owning devices and console processes on CPU servers
and that user's domain and encryption key are
read from NVRAM on all machines except PC's.
PC's keep the information in the disk partition
.BI /dev/sd XX /nvram\f1.
If a
.B -k
option is given or if no stored information is found
.I boot
will prompt for all three items and store them.
.IP
.EX
password: 
authid: bootes
authdom: research.bell-labs.com
.EE
.PP
The key is used for mutual authentication of the server and its clients.
The domain and id identify the owner of the key.
.PP
Once connected,
.I boot
behaves as on the terminal except for
.IR exec (2)'ing
.B /$objtype/init
.BR -c .
.SS Booting Methods
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
.BR tcp
connect via Ethernet using the TCP protocol.
The
.I args
are passed to
.IR ipconfig (8)
when configuring the IP stack.
The 
.IR plan9.ini (8)
variables
.B fs
and
.B auth
override the file server and authentication server IP addresses
obtained (if any) from DHCP during
.IR ipconfig (8).
.TP 8
.B local
connect to the local file system.
The first argument is a disk holding a file system.
.I Boot
inspects the disk.
.I Boot
will configure the IP stack by passing
.IR args ,
if any, to
.IR ipconfig (8).
.RE
.PP
For the
.B tcp
method,
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.
.SH EXAMPLES
On PCs, the default arguments to boot are constructed using
the 
.B bootargs
variable in
.IR plan9.ini (8).
.PP
Start 
.IR cwfs (4)
in config mode:
.IP
.EX
bootargs=local!/dev/sdC0/fscache -c
.EE
.LP
Use an IP stack on an alternate ethernet interface
with a static address and fixed file server and authentication
server addresses.
.IP
.EX
fs=192.168.0.2
auth=192.168.0.3
bootargs=tcp!-g 192.168.0.1 ether /net/ether1 \e
    192.168.0.50 255.255.255.0
.EE
.LP
(The 
.B bootargs
line is split only for presentation; it is one line in the file.)
.SH FILES
.B #s/boot
.br
.B #//boot/boot
.SH SOURCE
.B /sys/src/9/boot
.SH "SEE ALSO"
.IR root (3),
.IR dhcpd (8),
.IR init (8)
.SH BUGS
The use of
.B bootargs
in general is odd.