BOOT(8) BOOT(8)
NAME
boot - connect to the root file server
SYNOPSIS
/boot [ -fkm ] [ -uusername ] [ method!fs-addr ]
DESCRIPTION
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 exec(2)'s the init(8) program. It is started by
the kernel, never run directly by the user. See booting(8)
for information about the process of loading the kernel (and
boot) into memory.
Once loaded, the kernel initializes its data structures and
devices. It sets the two environment variables /env/cputype
and /env/terminal to describe the processor. It then binds
a place-holder file server, root(3), onto / and crafts an
initial process whose sole function is to exec(2) /boot, a
binary which is compiled into root(3).
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 boot.
On the PC, each line in the DOS file plan9.ini of the form
name=value is passed to the boot program as an environment
variable with the same name and value. The command line is
/386/9dos method!server
(The first argument is ignored by boot.) Boot must determine
the file server to use and a 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.
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. Boot will prompt for these.
Method and address are prompted for first. The prompt lists
all valid methods, with the default in brackets, for exam-
ple:
root is from (il, local!#S/sdC0/fs)[il]:
A newline picks the default. Other possible responses are
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BOOT(8) BOOT(8)
method or method!address. To aid in automatic reboot, the
default is automatically taken on CPU servers if nothing is
typed within 15 seconds.
The other interactions depend on whether the system is a
terminal or a CPU server.
Terminal
The terminal must have a username to set. If none is speci-
fied with the -u option, boot will prompt for one on the
console:
user:
The user will also be prompted for a password to be used as
an encryption key on each attach(5):
password:
With most methods boot can now connect to the file server.
However, with the serial line methods 9600 and 19200, the
actual mechanics of setting up the complete connection are
too varied to put into the boot program. Instead 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:
Connect to file system now, type ctrl-d when done.
(Use the view or down arrow key to send a break)
The user can now type at the modem to dial the number. What
is typed depends on the modem and is beyond this discussion.
When the user types a control-D, boot stops simulating a
terminal and starts the file system protocol over the serial
line.
Once connected, boot mounts the root file system before /
and makes the connection available as #s/boot for subsequent
processes to mount (see bind(2)). Boot completes by
exec(2)'ing /$objtype/init -t. If the -m option is given it
is also passed as an option to init.
If the kernel has been built with the cache file system,
cfs(4), the local disk partition /dev/sdXX/cache (where XX
is a unit specifier) exists, and the root file system is
from a remote server, then the kernel will insert a user
level cache process between the remote server and the local
namespace that caches all remote accesses on the local par-
tition. The -f flag commands cfs to reformat the cache par-
tition.
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BOOT(8) BOOT(8)
CPU Servers
The user owning devices and console processes on CPU servers
and that user's domain and encryption key are read from
NVRAM on all machines except PC's. PC's keep the informa-
tion in the disk partition /dev/sdXX/nvram. If a -k option
is given or if no stored information is found boot will
prompt for all three items and store them.
password:
authid: bootes
authdom: research.bell-labs.com
The key is used for mutual authentication of the server and
its clients. The domain and id identify the owner of the
key.
Once connected, boot behaves as on the terminal except for
exec(2)'ing /$objtype/init -c.
Booting Methods
The methods available to any system depend on what was com-
piled into the kernel. The complete list of booting methods
are listed below.
il connect via Ethernet using the IL protocol.
tcp connect via Ethernet using the TCP protocol. This
method is used only if the initial file server is on
a Unix system.
local connect to the local file system.
For the il and 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.
FILES
#s/boot
SOURCE
/sys/src/9/boot
SEE ALSO
root(3), dhcpd(8), init(8)
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