boot, bootrc – connect to the root file server
is the first program run after a kernel has been loaded. It
a compressed filesystem contained in
sets up the
environment and executes
passing on its arguments.
connects to the file server that will serve the root, performs any
authentication needed to connect to that server, and executes the
are started by the kernel, never run directly by the user.
for information about the process of loading the kernel (and
Once loaded, the kernel initializes its data structures and devices.
It sets the two environment variables
to describe the processor.
It then binds a place-holder file server,
and crafts an initial process whose sole function is to
a binary which is compiled into
The command line passed depends
on the information passed from boot ROM
Machines that boot directly from ROM (that is, most machines other than PCs)
pass the boot line given to the ROM directly to
On the PC, each line in the file
of the form
is passed to the boot program as an environment
variable with the same name and value.
passed its execution to
it must determine the fileserver to use and a
with which to connect to it.
will name a local disk partition or ethernet interface.
The complete list of methods is given below.
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
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
breaks into the
Other possible responses are
The other interactions depend on whether the system
terminal or a CPU server.
A terminal must have a
If not specified with the
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
the root file system before
and makes the connection available as
for subsequent processes to
option is given it is also passed as an option to
If the environment variable
is set (via
it is used as an argument to
has been built with the cache file system,
the local disk partition
is a unit specifier)
exists, and the root file system is from a remote server,
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 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
The key is used for mutual authentication of the server and its clients.
The domain and id identify the owner of the key.
behaves as on the terminal except for
The methods available to any system depend on what was
compiled into the kernel.
The complete list of booting methods are listed below.
connect via Ethernet using the TCP protocol.
are passed to
when configuring the IP stack.
override the file server and authentication servers
obtained (if any) from DHCP during
the same as
but uses the IL protocol to connect to the fileserver.
connect to the local file system.
is a disk partition file holding a file system.
inspects the disk partition with
to determine the file system type and starts the
appropriate server with
On PCs, the default arguments to boot are constructed using
in config mode:
Use an IP stack on an alternate ethernet interface
with a static address and fixed file server and authentication
bootargs=tcp!-g 192.168.0.1 ether /net/ether1 \
line is split only for presentation; it is one line in the file.)
The use of
in general is odd.
first appeared in Plan 9 from Bell Labs. It was rewritten
for 9front (April, 2011).