NAME
	  rshd - The remote shell server

     SYNOPSIS
	  rshd [-aln]

     FLAGS
	  -a   The addresses for the hostname are requested, verifying
	       that the	name and address correspond.

	  -l   Prevents	the ruserok command from doing any validation
	       based on	the user's .rhosts file, unless	the user is
	       the superuser.

	  -n   Disables	transport-level, keep-alive messages.

     DESCRIPTION
	  The rshd daemon 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.

	  The rshd daemon listens for service requests at the port
	  indicated in the cmd service specification; see services(4).
	  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 to 1023, the server	aborts
	       the connection.

	  2.   The server reads	bytes 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 nonzero, it is
	       interpreted as the port number of a secondary stream to
	       be used for the stderr option.  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 to	1023.

	  4.   The server checks the client's source address and
	       requests	the corresponding hostname (see
	       gethostbyaddr(3), hosts(4), and named(8)).  If the
	       hostname	cannot be determined, the dot-notation
	       representation of the host address is used.  If the
	       hostname	is in the same domain as the server (according
	       to the last two components of the domain	name), or if
	       the -a flag 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 username of at	most 16	bytes is
	       retrieved on the	initial	socket.	 This username is
	       interpreted as the user identity	on the client 's
	       machine.

	  6.   A null-terminated username of at	most 16	bytes is
	       retrieved on the	initial	socket.	 This username 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.   The rshd	daemon 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 flag prevents ruserok(3) from doing any valida-
	       tion 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 esta-
	       blished by rshd.

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

     CAUTION
	  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.

     DIAGNOSTICS
	  Except for the last diagnostic message listed, all diagnos-
	  tic 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 characters.

	  Remuser too long.
	  The name of the user on the remote machine is	longer than 16
	  characters.

	  Command too long.
	  The command line passed exceeds the size of the argument
	  list (as configured into the system).

	  Login	incorrect.
	  No password file entry for the username existed.

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

	  Permission denied.
	  The authentication procedure previously described failed.

	  Can't	make pipe.
	  The pipe needed for the stderr option, but it	was not
	  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
	  stderroption,	and is not preceded by a flag byte.

     FILES
	  /usr/sbin/rshd
	       Specifies the command path

     RELATED INFORMATION
	  rsh(1), rcmd(3), ruserok(3)