BOOT(8) BOOT(8)
NAME
boot, bootrc - connect to the root file server
SYNOPSIS
/boot/boot
DESCRIPTION
Boot is the first program run after a kernel has been
loaded. It mounts bootfs.paq, a compressed filesystem con-
tained in root(3), sets up the rc(1) environment and exe-
cutes bootrc passing on its arguments. Bootrc connects to
the file server that will serve the root, performs any
authentication needed to connect to that server, and exe-
cutes the init(8) program. Both boot and bootrc are 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/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 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.
After boot passed its execution to bootrc, it must determine
the fileserver to use and a method with which to connect to
it. Typically device will name a local disk partition or
ethernet interface. The complete 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 exam-
ple:
bootargs is (tcp, il, local!device) [local!/dev/sdC0/fscache]
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BOOT(8) BOOT(8)
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, 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:
Once connected, boot mounts the root file system at /root
(with the optional mount spec argument from $rootspec) and
makes the connection available as #s/boot for subsequent
processes to mount (see bind(2)). It then binds /root (or
the value specified by $rootdir) after the / directory.
Boot completes by exec(2)'ing /$cputype/init -t. If the -m
option is given it is also passed as an option to init. If
the environment variable init is set (via plan9.ini(8)), it
is used as an argument 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 names-
pace that caches all remote accesses on the local 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.
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.
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BOOT(8) BOOT(8)
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.
tcp connect via Ethernet using the TCP protocol. The
device and args are passed to ipconfig(8) when con-
figuring the IP stack. The plan9.ini(8) variables
fs and auth override the file server and authentica-
tion servers obtained (if any) from DHCP and IPv6
router advertisements during ipconfig(8).
il the same as tcp but uses the IL protocol to connect
to the fileserver.
tls makes an authenticated and encrypted connection to
the fileserver via srvtls using t9fs service (see
srv(4)). the arguments are the same as tcp.
local connect to the local file system. The device is a
disk partition file holding a file system. Bootrc
inspects the disk partition with fstype(1) to deter-
mine the file system type and starts the appropriate
server with args.
reboot starts another kernel. The device is of the form
bootfile [ ! method ] where bootfile is the path to
the kernel and method is any of the above boot meth-
ods that connects to the fileserver on where the
bootfile is located.
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 address 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
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BOOT(8) BOOT(8)
#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.
Filenames passed to 9bootfat must be specified in DOS 8.3
format. 9bootfat does not support long file names.
HISTORY
Boot first appeared in Plan 9 from Bell Labs. It was rewrit-
ten in rc for 9front (April, 2011).
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