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RSHD(8)			  BSD System Manager's Manual		       RSHD(8)

     rshd -- remote shell server

     rshd [-?DLaln]

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

     The rshd utility 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 NUL (`\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 cor-
	  responding host name (see gethostbyaddr(3), hosts(5) and named(8)).
	  If the hostname cannot be determined or the hostname and address do
	  not match after verification,	the dot-notation representation	of the
	  host address is used.

     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 iden-
	  tity 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 iden-
	  tity 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 up-
	  per bound on the size	of the system's	argument list.

     8.	  The rshd utility 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 NUL	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.

     The options are as	follows:

     -?	     Display the usage message,	and exit.

     -D	     Sets the TCP_NODELAY socket option, which improves	the perfor-
	     mance of small back-to-back writes	at the expense of additional
	     network traffic.

     -L	     Causes all	successful accesses to be logged to syslogd(8) as messages.

     -a	     This flag is ignored, and is present for compatability purposes.

     -l	     Do	not use	the user's .rhosts file	for authentication, unless the
	     user is the superuser.

     -n	     Turn off transport	level keepalive	messages.  This	will prevent
	     sessions from timing out if the client crashes or becomes un-

     Except for	the last one listed below, all diagnostic messages are re-
     turned 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 10 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

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

     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 user name existed or the authenti-
	     cation procedure described	above failed.

     Remote directory.
	     The chdir(2) function to the home directory failed.

     Logins not	available right	now.
	     The rsh(1)	utility	was attempted outside the allowed hours	de-
	     fined in /etc/login.conf for the local user's login class.

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

     Can't fork; try again.
	     A fork(2) by the server failed.

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

     rlogin(1),	rsh(1),	gethostbyaddr(3), rcmd(3), ruserok(3), auth.conf(5),
     hosts(5), hosts.equiv(5), login.conf(5), services(5), named(8),
     rlogind(8), syslogd(8)


     /etc/pam.conf     rshd uses /etc/pam.conf entries with service name
		       "rsh".  Authentication modules requiring	passwords
		       (such as	pam_unix) are not supported.

     The authentication	procedure used here assumes the	integrity of each
     client machine and	the connecting medium.	This is	insecure, but is use-
     ful 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.

     IPv6 support was added by WIDE/KAME project.

BSD				 June 4, 1993				   BSD


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