term% cat index.txt BOOT(8) System Manager's Manual BOOT(8)
NAME
boot, bootrc - connect to the root file server
SYNOPSIS
/boot/boot [ -fkm ] [ -uusername ] [ method!device ] [ args ]
DESCRIPTION
Boot is the first program run after a kernel has been loaded. It mounts
bootfs.paq, a compressed filesystem contained in root(3), sets up the
rc(1) environment and executes bootrc passing on its arguments. Bootrc
connects to the file server that will serve the root, performs any au‐
thentication needed to connect to that server, and executes the init(8)
program. Both boot and bootrc are started by the kernel, never run di‐
rectly 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/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 ma‐
chines other than PCs) pass the boot line given to the ROM directly to
boot.
On the PC, each line in the file plan9.ini(8) 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
/boot/boot method!device
After boot passed its execution to bootrc, it must determine the file‐
server to use and a method with which to connect to it. Typically de‐
vice will name a local disk partition or ethernet interface. The com‐
plete list of methods is given below.
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.
Bootrc will prompt for these.
Method and device are prompted for first. The prompt lists all valid
methods, with the default in brackets, for example:
bootargs is (tcp, il, local!device) [local!/dev/sdC0/fscache]
A newline picks the default. Entering !rc breaks into the rc(1) shell.
Other possible responses are method, method!device or method!device
args.
The other interactions depend on whether the system is a terminal or a
CPU server.
Terminal
A terminal must have a username set. If not specified with the user=
plan9.ini(8) parameter or 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 encryp‐
tion key on each attach(5):
password:
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 /$cputype/init -t. If the -m
option is given it is also passed as an option to init. If the envi‐
ronment variable init is set (via plan9.ini(8)), it is used as an argu‐
ment to exec(2) instead.
If the bootfs.paq has been built with the cache file system, cfs(4),
the local disk partition /dev/sdXX/cache (where XX is a unit specifier)
exists, and the root file system is from a remote server, then bootrc
will insert a user level cache process between the remote server and
the local namespace that caches all remote accesses on the local parti‐
tion. The -f flag commands cfs(4) to reformat the cache partition.
CPU Servers
The user owning devices and console processes on CPU servers and that
user's domain and encryption key are read from NVRAM on all machines
except PCs. PCs keep the information in the disk partition
/dev/sdXX/nvram. If a -k option is given or if no stored information
is found boot will prompt for all three items and store them.
password:
authid: bootes
authdom: research.bell-labs.com
The key is used for mutual authentication of the server and its
clients. The domain and id identify the owner of the key.
Once connected, boot behaves as on the terminal except for exec(2)'ing
/$cputype/init -c.
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.
tcp connect via Ethernet using the TCP protocol. The device and
args are passed to ipconfig(8) when configuring the IP stack.
The plan9.ini(8) variables fs and auth override the file server
and authentication servers obtained (if any) from DHCP during
ipconfig(8).
il the same as tcp but uses the IL protocol to connect to the
fileserver.
local connect to the local file system. The device is a disk parti‐
tion file holding a file system. Bootrc inspects the disk par‐
tition with fstype(1) to determine the file system type and
starts the appropriate server with args.
EXAMPLES
On PCs, the default arguments to boot are constructed using the
bootargs variable in plan9.ini(8).
Start cwfs(4) in config mode:
bootargs=local!/dev/sdC0/fscache -c
Use an IP stack on an alternate ethernet interface with a static ad‐
dress and fixed file server and authentication server addresses.
fs=192.168.0.2
auth=192.168.0.3
bootargs=tcp!-g 192.168.0.1 ether /net/ether1 \
192.168.0.50 255.255.255.0
(The bootargs line is split only for presentation; it is one line in
the file.)
FILES
#s/boot
#//boot/boot
#//boot/bootfs.paq
SOURCE
/sys/src/9/boot
SEE ALSO
root(3), dhcpd(8), init(8)
BUGS
The use of bootargs in general is odd.
HISTORY
Boot first appeared in Plan 9 from Bell Labs. It was rewritten in rc
for 9front (April, 2011).
BOOT(8)