rshd man page on Xenix

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RSHD(8)								       RSHD(8)

NAME
       rshd - remote shell server

SYNOPSIS
       rshd [-aln]

DESCRIPTION
       Rshd  is	 the server for the rcmd(3) routine and, consequently, for the
       rsh(1) program.	The server provides remote execution  facilities  with
       authentication based on privileged port numbers from trusted hosts.

       Rshd  listens for service requests at the port indicated in the ``cmd''
       service specification; see services(5).	 When  a  service  request  is
       received the following protocol is initiated:

       1)     The  server checks the client's source port.  If the port is not
	      in the range 512-1023, the server aborts the connection.

       2)     The server reads characters from the socket up to a null	(`\0')
	      byte.   The  resultant string is interpreted as an ASCII number,
	      base 10.

       3)     If the number received in step 2 is non-zero, it is  interpreted
	      as  the  port  number  of	 a secondary stream to be used for the
	      stderr.  A second connection is then created  to	the  specified
	      port  on	the  client's machine.	The source port of this second
	      connection is also in the range 512-1023.

       4)     The server checks the client's source address and	 requests  the
	      corresponding  host  name	 (see  gethostbyaddr(3),  hosts(5) and
	      named(8)).  If the hostname cannot be determined, the  dot-nota‐
	      tion  representation  of the host address is used.  If the host‐
	      name is in the same domain as the server (according to the  last
	      two  components  of  the	domain	name),	or if the -a option is
	      given, the addresses for the hostname are	 requested,  verifying
	      that  the	 name and address correspond.  If address verification
	      fails, the  connection  is  aborted  with	 the  message,	``Host
	      address mismatch.''

       5)     A	 null  terminated  user	 name  of  at  most  16	 characters is
	      retrieved on the initial socket.	This user name is  interpreted
	      as the user identity on the client's machine.

       6)     A	 null  terminated  user	 name  of  at  most  16	 characters is
	      retrieved on the initial socket.	This user name is  interpreted
	      as a user identity to use on the server's machine.

       7)     A	 null  terminated command to be passed to a shell is retrieved
	      on the initial socket.  The length of the command is limited  by
	      the upper bound on the size of the system's argument list.

       8)     Rshd  then  validates  the user using ruserok(3), which uses the
	      file ``/etc/hosts.equiv'' and the ``.rhosts'' file found in  the
	      user's  home  directory.	The -l option prevents ruserok(3) from
	      doing any validation  based  on  the  user's  ``.rhosts''	 file,
	      unless the user is the superuser.

       9)     A	 null  byte  is returned on the initial socket and the command
	      line is passed to the normal login shell of the user.  The shell
	      inherits the network connections established by rshd.

       Transport-level	keepalive messages are enabled unless the -n option is
       present.	 The use of keepalive messages allows sessions to be timed out
       if the client crashes or becomes unreachable.

DIAGNOSTICS
       Except  for  the	 last  one  listed  below, all diagnostic messages are
       returned on the initial socket, after which any network connections are
       closed.	 An  error is indicated by a leading byte with a value of 1 (0
       is returned in step 9 above upon successful completion of all the steps
       prior to the execution of the login shell).

       ``locuser too long''
       The  name of the user on the client's machine is longer than 16 charac‐
       ters.

       ``remuser too long''
       The name of the user on the remote machine is longer  than  16  charac‐
       ters.

       ``command too long ''
       The  command line passed exceeds the size of the argument list (as con‐
       figured into the system).

       ``Login incorrect.''
       No password file entry for the user name existed.

       ``No remote directory.''
       The chdir command to the home directory failed.

       ``Permission denied.''
       The authentication procedure described above failed.

       ``Can't make pipe.''
       The pipe needed for the stderr, wasn't created.

       ``Can't fork; try again.''
       A fork by the server failed.

       ``<shellname>: ...''
       The user's login shell could not be started.  This message is  returned
       on  the connection associated with the stderr, and is not preceded by a
       flag byte.

SEE ALSO
       rsh(1), rcmd(3), ruserok(3)

BUGS
       The authentication procedure used here assumes the  integrity  of  each
       client  machine	and  the  connecting medium.  This is insecure, but is
       useful in an ``open'' environment.

       A facility to allow all	data  exchanges	 to  be	 encrypted  should  be
       present.

       A more extensible protocol (such as Telnet) should be used.

4.2 Berkeley Distribution	 June 24, 1990			       RSHD(8)
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