ref: 5a93b4fe2d4b76815ce06ba411f80a49fe26b3a1
dir: /sys/man/8/boot/
.TH BOOT 8
.SH NAME
boot, bootrc \- connect to the root file server
.SH SYNOPSIS
.B /boot/boot
.SH DESCRIPTION
.I Boot
is the first program run after a kernel has been loaded. It
mounts
.BR bootfs.paq ,
a compressed filesystem contained in
.IR root (3),
sets up the
.IR rc (1)
environment and executes
.I bootrc
passing on its arguments.
.I Bootrc
connects to the file server that will serve the root, performs any
authentication needed to connect to that server, and executes the
.IR init (8)
program. Both
.I boot
and
.I bootrc
are 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 file
.IR plan9.ini (8)
of the form
.IB name = value
is passed to the boot program as an environment
variable with the same name and value.
.PP
After
.I boot
passed its execution to
.I bootrc,
it must determine the fileserver to use and a
.I method
with which to connect to it.
Typically
.I device
will name a local disk partition or ethernet interface.
The complete list of methods is given below.
.PP
.I Bootrc
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 Bootrc
will prompt for these.
.PP
Method and device are prompted for first.
The prompt lists all valid methods, with the default in brackets, for example:
.IP
.EX
bootargs is (tcp, il, local!device) [local!/dev/sdC0/fscache]
.EE
.PP
A newline picks the default. Entering
.B !rc
breaks into the
.IR rc (1)
shell.
Other possible responses are
.IR method ,
.IB method ! device
or
.IB method ! device
.IR args .
.PP
The other interactions depend on whether the system
is a
terminal or a CPU server.
.SS Terminal
A terminal must have a
.I username
set.
If not specified with the
.B user=
.IR plan9.ini (8)
parameter,
.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
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 /$cputype/init
.BR -t .
If the
.B -m
option is given it is also passed as an option to
.IR init .
If the environment variable
.B init
is set (via
.IR plan9.ini (8)),
it is used as an argument to
.IR exec (2)
instead.
.PP
If the
.I bootfs.paq
has been built with the cache file system,
.IR cfs (4),
the local disk partition
.BI /dev/sd XX /cache
(where
.B XX
is a unit specifier)
exists, and the root file system is from a remote server,
then
.I bootrc
will insert a user level cache
process between the remote server and the local namespace
that caches all remote accesses on the local partition.
.SS CPU Servers
The user owning devices and console processes on CPU servers
and that user's domain and encryption key are
read from NVRAM on all machines except PCs.
PCs keep the information in the disk partition
.BI /dev/sd XX /nvram.
.IP
.EX
password:
authid: bootes
authdom: research.bell-labs.com
.EE
.PP
The key is used for mutual authentication of the server and its clients.
The domain and id identify the owner of the key.
.PP
Once connected,
.I boot
behaves as on the terminal except for
.IR exec (2)'ing
.B /$cputype/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 device
and
.I args
are passed to
.IR ipconfig (8)
when configuring the IP stack.
The
.IR plan9.ini (8)
variables
.B fs
and
.BR auth
override the file server and authentication servers
obtained (if any) from DHCP during
.IR ipconfig (8).
.TP 8
.BR il
the same as
.B tcp
but uses the IL protocol to connect to the fileserver.
.TP 8
.BR local
connect to the local file system.
The
.I device
is a disk partition file holding a file system.
.I Bootrc
inspects the disk partition with
.IR fstype (1)
to determine the file system type and starts the
appropriate server with
.IR args .
.RE
.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
.br
.B #//boot/bootfs.paq
.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.
.SH HISTORY
.I Boot
first appeared in Plan 9 from Bell Labs. It was rewritten
in
.I rc
for 9front (April, 2011).