.TH CPU 1
.SH NAME
cpu \- connection to CPU server
.SH SYNOPSIS
.B cpu
[
.B -p
] [
.B -h
.I server
] [
.B -u
.I user
] [
.B -a
.I auth-method
] [
.B -P
.I patternfile
] [
.B -e
.I encryption-hash-algs
] [
.B -k
.I keypattern
] [
.B -c
.I cmd args ...
]
.PP
.B cpu
[
.B -n
] [
.B -A
.I address
] [
.B -R
|
.B -O
]
.SH DESCRIPTION
.I Cpu
starts an
.IR rc (1)
running on the
.I server
machine, or the machine named in the
.B $cpu
environment variable if there is no
.B -h
option.
.IR Rc 's
standard input, output, and error files will be
.B /dev/cons
in the name space where the
.I cpu
command was invoked.
Normally,
.I cpu
is run in an
.IR rio (1)
window on a terminal, so
.IR rc
output goes to that window, and input comes from the keyboard
when that window is current.
.IR Rc 's
current directory is
the working directory of the
.I cpu
command itself.
.PP
The name space for the new
.I rc
is an analogue of the name space where the
.I cpu
command was invoked:
it is the same except for architecture-dependent bindings such as
.B /bin
and the use of fast paths to file servers, if available.
.PP
If a
.B -u
argument is present,
.I cpu
uses the argument as the remote user id.
.PP
If a
.B -c
argument is present, the remainder of the command line is executed by
.I rc
on the server, and then
.I cpu
exits.
.PP
If a
.B -P
argument is present, the
.I patternfile
is passed to
.IR exportfs (4)
to control how much of the local name space will be exported to
the remote system.
.PP
The
.B -a
command allows the user to specify the authentication mechanism used
when connecting to the remote system.  The two possibilities for
.I auth-method
are:
.TF netkey
.TP
.B p9
This is the default.  Authentication is done using the standard Plan 9
mechanisms, (see
.IR authsrv (6)).
No user interaction is required.
.TP
.B netkey
Authentication is done using challenge/response and a hand held
authenticator or the
.I netkey
program
(see
.IR passwd (1)).
The user must encrypt the challenge and type the encryption
back to
.IR cpu .
This is used if the local host is in a different protection domain than
the server or if the user wants to log into the server as a different
user.
.TP
.B none
This skips authentication. This requires the
.IR -n
flag to be specified on the remote side.
.PD
.PP
The
.B -e
option specifies an encryption and/or hash algorithm to
use for the connection.  If both are specified, they must
be space separated and comprise a single argument, so they
must be quoted if in a shell command.  The default is
.L rc4_256
encryption and
.L sha1
hashing.  See
.IR ssl (3)
for details on possible algorithms.  The argument
.L clear
specifies no encryption algorithm and can be used to talk
to older versions of the
.I cpu
service.
.PP
The
.B -k
flag specifies a key pattern to use to restrict the keys
selected by the
.I auth_proxy
call used for authentication.
.PP
The name space is built by running
.B /usr/$user/lib/profile
with the root of the invoking name space bound to
.BR /mnt/term .
The
.B service
environment variable is set to
.BR cpu ;
the
.B cputype
and
.B objtype
environment variables reflect the server's architecture.
.PP
The
.B -R
flag causes
.I cpu
to run the server (remote) side of the protocol.
It is run from service files such as
.BR /bin/service/tcp17010 .
The
.B -O
flag is similar but simulates the pre-9P2000 version
of the 
.I cpu
protocol.
The
.B -n
option allows using the
.B none
authentication method for incoming connections and must be
specified before the
.B -R
and
.B -O
flags.
.PP
The
.B -p
flag pushes the
.IR aan (8)
filter onto the connection to protect against temporary
network outages.
.PP
The
.B -A
flag sets the announce-string
.I address
to use for
.IR aan (8)
connections, if requested by the initial protocol.
.SH FILES
The name space of the terminal side of the
.I cpu
command is mounted, via
.IR exportfs (4),
on the CPU side on directory
.BR /mnt/term .
The files such as
.B /dev/cons
are bound to their standard locations from there.
.SH SOURCE
.B /sys/src/cmd/cpu.c
.SH SEE ALSO
.IR rc (1) ,
.IR rio (1) ,
.IR exportfs (4) ,
.IR aan (8)
.SH BUGS
Binds and mounts done after the terminal
.B lib/profile
is run are not reflected in the new name space.
.PP
By default, the entire namespace of the local system is
exported to the remote system. Use of the
.B -P
option in conjunction with a customized patternfile can
limit this exposure, but also limits the usefulness of
.B /mnt/term.