boot - connect to the root file server
/boot [ -fkm ] [ -uusername ] [ method!fs-addr ]
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. On the
MIPS Magnum and SGI Power Series the command line passed to boot is the same as that given
to the ROM monitor.
On AT&T Gnots the command line is
On the Nextstation , no information is passed from the boot ROM or program. The command
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
Boot must determine the file server to use and a method with which to connect to it. It
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.
root is from (il, tcp, hs, local)[il]:
A newline picks the default. Other possible responses are 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.
The terminal must have a username to set. If none is specified with the -u option, boot
will prompt for one on the console:
The user will also be prompted for a password to be used as an encryption key on each
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 a modem or a Datakit destination please: interface to set up the
connection to a TSM8 card. At Murray Hill, a user would type nj/astro/plan85 at this
point. 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 avail-
able as #s/boot for subsequent processes to mount (see bind(2)). Boot completes by
exec(2)'ing /$objtype/init -t. If the -m option is given it is also passed as an option
If the kernel has been built with the cache file system, cfs(4), the local disk partition
/dev/[sh]dcache exists, and the root file system is from a remote server, then the
kernel will insert a user level cache process between the remote server and the local
namespace that caches all remote accesses on the local partition. The -f flag commands
cfs to reformat the cache partition.
The user owning devices and console processes on CPU servers and that user's domain and
encryption key are read from NVRAM on all machines except PC's. PC's keep the information
in the disk partition /dev/[sh]dnvram. If a -k option is given or if no stored infor-
mation is found boot will prompt for all three items and store them.
The key is used for mutual authentication of the server and its clients. The domain and
id identify the owner of the key.
Once connected, boot behaves as on the terminal except for exec(2)'ing /$objtype/init -c.
The methods available to any system depend on what was compiled into the kernel. The com-
plete list of booting methods are listed below.
cyc connect via a point-to-point fiber link using Cyclone boards. If specified, the
address must be the number of the Cyclone board to be used, default 0.
il connect via Ethernet using the IL protocol.
tcp connect via Ethernet using the TCP protocol. This method is used only if the ini-
tial file server is on a Unix system.
hs connect via Datakit using the high speed Datakit card.
incon connect via Datakit using the Incon interface.
9600 connect via Datakit using the serial interface at 9600 baud.
19200 connect via Datakit using the serial interface at 19200 baud.
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. For the Datakit methods, hs,
9600, 19200, and incon, the address must be specified and must be a relative path name to
the file server. If no address is specified, the address Nfs is used.
root(3), bootp(8), init(8)