.TH ATTACH 5 
.SH NAME
attach, session, nop \- messages to initiate activity
.SH SYNOPSIS
.ta \w'\fLTsession 'u
.B Tnop	
.IR tag [2]
.br
.B Rnop	
.IR tag [2]
.PP
.B
Tsession	
.IR tag [2]
.IR chal [8]
.br
.B
Rsession	
.IR tag [2]
.IR chal [8]
.IR authid [28]
.IR authdom [48]
.PP
.B
Tattach	
.IR tag [2]
.IR fid [2]
.IR uid [28]
.IR aname [28]
.IR ticket [72]
.IR auth [13]
.br
.B
Rattach	
.IR tag [2]
.IR fid [2]
.IR qid [8]
.IR rauth [13]
.SH DESCRIPTION
The
.B nop
request does nothing overt but may be used to synchronize the
channel between two service hosts initially.
.PP
The
.B session
request is used to initialize a connection between a client and a server.
All outstanding I/O on the connection is aborted.
The set of messages between
.B session
requests is called a
.IR session .
The host's user name
.RI ( authid )
and its authentication domain 
.RI ( authdom )
identify the key to be used when authenticating to this host.
The exchanged challenges
.RI ( chal )
are used in the authentication algorithm.
If
.I authid
is a null string no authentication is performed in this session.
.PP
The
.I tag
should be
.B NOTAG
(value
.BR 0xFFFF )
for a
.B nop
or
.B session
message.
.PP
The
.B attach
message serves as a fresh introduction from a user on
the client machine to a server.
The message identifies the user
.RI ( uid )
and may select
the file tree to access
.RI ( aname ).
The
.I ticket
and
.I auth
arguments contains authorization data
derived from the exchanged challenges
of the
.B session
message; see
.IR auth (6).
.PP
As a result of the
.B attach
transaction, the client will have a connection to the root
directory of the desired file tree,
represented by
.IR fid .
An error is returned if
.I fid
is already in use.
The server's idea of the root of the file tree is represented by the returned
.BR qid .
.SH ENTRY POINTS
An
.B attach
transaction will be generated for kernel devices
(see
.IR intro (3))
when a system call evaluates a file name
beginning with
.LR # .
.IR Pipe (2)
generates an attach on the kernel device
.IR pipe (3).
The
.I mount
system call
(see
.IR bind (2))
generates an
.B attach
messages to the remote file server.
When the kernel boots, an
.I attach
is made to the root device,
.IR root (3),
and then an
.B attach
is made to the requested file server machine.
.SH SEE ALSO
.IR auth (6)