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RSHD(1M)							      RSHD(1M)

NAME    [Toc]    [Back]

     rshd - remote shell server

SYNOPSIS    [Toc]    [Back]

     /usr/etc/rshd [-alnL]

DESCRIPTION    [Toc]    [Back]

     Rshd is the server	for the	rcmd(3N) routine and, consequently, for	the
     rsh(1C) program.  The server provides remote execution facilities with
     authentication based on privileged	port numbers from trusted hosts.  The
     -a	option verifies	the remote host	name and address match on all incoming
     connections.  Normally this check is performed only for connections from
     hosts in the local	domain.	 The -l	option disables	validation using
     .rhosts files.  Transport-level keep-alive	messages are enabled unless
     the -n option is present.	The use	of keep-alive messages allows sessions
     to	be timed out if	the client crashes or becomes unreachable.  The	-L
     option causes all successful accesses to be logged	to syslogd(1M) as
     auth.info messages.  These	options	should specified in the
     /etc/inetd.conf file (see inetd(1M)).

     Rshd 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 512-1023, 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 in
	 the range 513-1023.

     4)	 The server checks the client's	source address and requests the
	 corresponding host name (see gethostbyaddr(3N), hosts(4) and
	 named(1M)).  If the hostname cannot be	determined, 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
	 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.

									Page 1

RSHD(1M)							      RSHD(1M)

     8)	 Rshd then validates the user according	to the following steps.	 The
	 local (server-end) user name is looked	up in the password file.  If
	 the lookup fails, the connection is terminated.  Rshd then tries to
	 validate the user using ruserok(3N), which uses the file
	 /etc/hosts.equiv and the .rhosts file found in	the user's home
	 directory.  If	the user is not	the super-user,	(user id 0), the file
	 /etc/hosts.equiv is consulted for a list of hosts considered
	 ``equivalent''.  If the client's host name is present in this file,
	 the authentication is considered successful.  If the lookup fails, or
	 the user is the super-user, then the file .rhosts in the home
	 directory of the remote user is checked for the machine name and
	 identity of the user on the client's machine.	If this	lookup fails,
	 the connection	is terminated.	The -l option prevents ruserok(3N)
	 from doing any	validation based on the	user's ``.rhosts'' file,
	 unless	the user is the	superuser.

	 Under Trusted IRIX/CMW, only the first	field of the /etc/hosts.equiv
	 and $HOME/.rhosts files is relevant to	the system.  The second	field
	 is ignored as a comment.  This	behavior places	a restriction on the
	 rsh and rlogin	programs, which	do not allow unchallenged access
	 (access without demanding a password) unless the remote user name and
	 user ID are exactly identical to the local user name and user ID.  If
	 a different name or user ID is	used, the user is prompted for a
	 password that authenticates the user's	identity in the	usual manner.
	 The MAC label of the $HOME/.rhosts file must be dominated by the MAC
	 label of the login session, otherwise the user	will be	prompted for a
	 password.  It is recommended that the $HOME/.rhosts file be labeled
	 such that it is dominated by all other	labels that the	user can login

     9)	 If the	file /etc/nologin exists and the user is not the super-user,
	 the connection	is closed.

     10) 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.

SHARE II ACTIONS    [Toc]    [Back]

     If	the Share II system is installed and enabled, then the following
     privilege and resource checks are made immediately	after validation
     checks are	passed but before the shell is started:

     1.	 If your nologin flag is set, or you already have another connection
	 and your onelogin flag	is set,	then you are denied connection.

     2.	 If a disk usage exceeds its soft disk limit in	any of your domains,
	 then a	message	is printed and you are given a warning.	 If you
	 accumulate too	many warnings, further connection attempts are denied
	 and you must see your subadministrator	to rectify the situation.
	 Whenever you connect with no disk usages in excess of any soft
	 limits, all your accumulated warnings are cleared.

									Page 2

RSHD(1M)							      RSHD(1M)

     3.	 If you	do not have permission to use an rsh connection, as determined
	 by the	terminal permission flag terminal.flag.rsh, then you are
	 denied	connection.

     4.	 Some installations place limits on terminal connect-time, which apply
	 equally to connection by way of rsh.  If you have already reached
	 your connect-time limit, then you are denied connection.  Otherwise,
	 if you	have a limit, your remaining connect-time is printed.

     If	all of these checks are	passed,	rshd proceeds normally.

     For each new instance of a	remotely initiated process, rshd first reads
     the configuration file /etc/default/rshd.	Currently the only switch in
     this file is SVR4_SIGNALS,	which indicates	if SVR4	signal defaults	should
     be	used, and defaults to `YES'. This means	that processes spawned by rshd
     will run with the SIGXFSZ and SIGXCPU signals disabled (i.e. ignored).
     For CPU and filesize resource limiting to work correctly, this file
     should be edited and SVR4_SIGNALS set to `NO', so that these signal
     retain their default behaviour, which is to terminate the process.

FILES    [Toc]    [Back]

     /etc/limconf	 The compiled Share II configuration file (machine

     /etc/default/rshd	 Default behaviour configuration file

SEE ALSO    [Toc]    [Back]

     login(1), rsh(1C),	rexecd(1M), rcmd(3N), ruserok(3N), share(5)

DIAGNOSTICS    [Toc]    [Back]

     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 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

     ``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 user name existed.	(Logged	to the
     syslogd(1M) daemon	as an auth.notice message.)

									Page 3

RSHD(1M)							      RSHD(1M)

     ``No remote directory.''
     The chdir command to the home directory failed.  (Logged as an
     auth.notice message.)

     ``Permission denied.''
     The authentication	procedure described above failed.  (Logged as an
     auth.notice message.)

     ``Connection received using IP options (ignored)''
     The remote	host tried to use explicit IP source routing.

     ``Connection from <host> on illegal port''
     The remote	host used a nonprivileged port.

     ``Can't find name for <address>''
     No	hostname was found for the IP address.	The authentication procedure
     described above will use the IP address.

     ``Host addr <x> not listed	for host <y>''
     The remote	host's name and	address	did not	match.	The authentication
     procedure described above will use	the IP address instead of the name.

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

     ``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

     The Share II specific diagnostic messages are listed as follows:

     ``Warning <X> of <Y>: soft	disk limit exceeded.''
     One of your domains has a disk usage in excess of its soft	limit.

     ``Connection denied.  Too many warnings.''
     You have reached your warning limit.  See your subadministrator.

     ``Connection denied.  Already logged in - only one	login allowed.''
     You are already connected to the system and your onelogin flag is set.

     ``Connection denied.  Currently barred from logging in.''
     Your nologin flag is set.

     ``Connection denied.  No permission to use	this terminal.''
     You are not allowed to log	in at this terminal because of a clear
     terminal.flag.rsh flag.

									Page 4

RSHD(1M)							      RSHD(1M)

     ``You have	a remaining terminal connect-time of <Y>.''
     You may use this connection until you have	used up	your remaining
     connect-time, at which point you are forced to disconnect.

     ``Connection denied.  Terminal connect-time limit exceeded.''
     You have already reached your terminal connect-time limit.

     ``Share not configured - no limit checks.''
     The configuration file is unreadable for some reason, so terminal
     privileges, connect-time limits and disk space limits could not be

BUGS    [Toc]    [Back]

     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	should be used.

NOTES    [Toc]    [Back]

     rshd will set the LANG environment	variable if it is specified in

									PPPPaaaaggggeeee 5555
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