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ATTACH(5)                     File Formats Manual                    ATTACH(5)

       attach, session, nop - messages to initiate activity

       Tnop      tag[2]
       Rnop      tag[2]

       Tsession  tag[2] chal[8]
       Rsession  tag[2] chal[8] authid[28] authdom[48]

       Tattach   tag[2] fid[2] uid[28] aname[28] ticket[72] auth[13]
       Rattach   tag[2] fid[2] qid[8] rauth[13]

       The  nop  request does nothing overt but may be used to synchronize the
       channel between two service hosts initially.

       The 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 session requests  is  called  a  session.   The
       host's user name (authid) and its authentication domain (authdom) iden-
       tify the key  to  be  used  when  authenticating  to  this  host.   The
       exchanged  challenges  (chal) are used in the authentication algorithm.
       If authid is a null string no authentication is performed in this  ses-

       The tag should be NOTAG (value 0xFFFF) for a nop or session message.

       The  attach  message  serves as a fresh introduction from a user on the
       client machine to a server.  The message identifies the user (uid)  and
       may  select the file tree to access (aname).  The ticket and auth argu-
       ments contains authorization data derived from the exchanged challenges
       of the session message; see auth(6).

       As  a  result of the attach transaction, the client will have a connec-
       tion to the root directory of the desired  file  tree,  represented  by
       fid.  An error is returned if fid is already in use.  The server's idea
       of the root of the file tree is represented by the returned qid.

       An attach  transaction  will  be  generated  for  kernel  devices  (see
       intro(3))  when  a  system  call  evaluates  a file name beginning with
       Pipe(2) generates an attach on the kernel device  pipe(3).   The  mount
       system  call  (see  bind(2)) generates an attach messages to the remote
       file server.  When the kernel boots, an attach  is  made  to  the  root
       device,  root(3),  and  then  an  attach  is made to the requested file
       server machine.