[unix-history] / usr / man / man8 / rshd.8c

.TH RSHD 8C "4 March 1983"
.UC 4
.SH NAME
rshd \- remote shell server
.SH SYNOPSIS
.B /etc/rshd
.SH DESCRIPTION
.I Rshd
is the server for the 
.IR rcmd (3X)
routine and, consequently, for the
.IR rsh (1C)
program.  The server provides remote execution facilities
with authentication based on privileged port numbers.
.PP
.I Rshd
listens for service requests at the port indicated in
the ``cmd'' service specification; see
.IR services (5).
When a service request is received the following protocol
is initiated:
.IP 1)
The server checks the client's source port.
If the port is not in the range 0-1023, the server
aborts the connection.
.IP 2)
The server reads characters from the socket up
to a null (`\e0') byte.  The resultant string is
interpreted as an ASCII number, base 10.
.IP 3)
If the number received in step 1 is non-zero,
it is interpreted as the port number of a secondary
stream to be used for the 
.BR 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 0-1023.
.IP 4)
The server checks the client's source address.
If the address is associated with a host for which no
corresponding entry exists in the host name data base (see
.IR hosts (5)),
the server aborts the connection.
.IP 5)
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
.BR server 's
machine.
.IP 6)
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
.BR client 's
machine.
.IP 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.  
.IP 8)
.I Rshd
then validates the user according to the following steps.
The remote user name is looked up in the password file
and a
.I chdir
is performed to the user's home directory.  If either
the lookup or 
.I chdir
fail, the connection is terminated.
If the user is not the super-user, (user id 0), the file 
.I /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
.I .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.
.IP 9)
A null byte is returned on the connection associated
with the
.B stderr 
and the command line is passed to the normal login
shell of the user.  The
shell inherits the network connections established
by
.IR rshd .
.SH DIAGNOSTICS
All diagnostic messages are returned on the connection
associated with the
.BR stderr ,
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 command execution).
.PP
.B ``locuser too long''
.br
The name of the user on the client's machine is
longer than 16 characters.
.PP
.B ``remuser too long''
.br
The name of the user on the remote machine is
longer than 16 characters.
.PP
.B ``command too long ''
.br
The command line passed exceeds the size of the argument
list (as configured into the system).
.PP
.B ``Hostname for your address unknown.''
.br
No entry in the host name database existed for
the client's machine.
.PP
.B ``Login incorrect.''
.br
No password file entry for the user name existed.
.PP
.B ``No remote directory.''
.br
The 
.I chdir
command to the home directory failed.
.PP
.B ``Permission denied.''
.br
The authentication procedure described above failed.
.PP
.B ``Can't make pipe.''
.br
The pipe needed for the 
.BR stderr ,
wasn't created.
.PP
.B ``Try again.''
.br
A
.I fork
by the server failed.
.PP
.B ``/bin/sh: ...''
.br
The user's login shell could not be started.
.SH SEE ALSO
rsh(1C),
rcmd(3X)
.SH 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.
.PP
A facility to allow all data exchanges to be encrypted should be
present.
Commit	Line	Data
ccea61f9 C	1	.TH RSHD 8C "4 March 1983"
	2	.UC 4
	3	.SH NAME
	4	rshd \- remote shell server
	5	.SH SYNOPSIS
	6	.B /etc/rshd
	7	.SH DESCRIPTION
	8	.I Rshd
	9	is the server for the
	10	.IR rcmd (3X)
	11	routine and, consequently, for the
	12	.IR rsh (1C)
	13	program. The server provides remote execution facilities
	14	with authentication based on privileged port numbers.
	15	.PP
	16	.I Rshd
	17	listens for service requests at the port indicated in
	18	the ``cmd'' service specification; see
	19	.IR services (5).
	20	When a service request is received the following protocol
	21	is initiated:
	22	.IP 1)
	23	The server checks the client's source port.
	24	If the port is not in the range 0-1023, the server
	25	aborts the connection.
	26	.IP 2)
	27	The server reads characters from the socket up
	28	to a null (`\e0') byte. The resultant string is
	29	interpreted as an ASCII number, base 10.
	30	.IP 3)
	31	If the number received in step 1 is non-zero,
	32	it is interpreted as the port number of a secondary
	33	stream to be used for the
	34	.BR stderr .
	35	A second connection is then created to the specified
	36	port on the client's machine. The source port of this
	37	second connection is also in the range 0-1023.
	38	.IP 4)
	39	The server checks the client's source address.
	40	If the address is associated with a host for which no
	41	corresponding entry exists in the host name data base (see
	42	.IR hosts (5)),
	43	the server aborts the connection.
	44	.IP 5)
	45	A null terminated user name of at most 16 characters
	46	is retrieved on the initial socket. This user name
	47	is interpreted as a user identity to use on the
	48	.BR server 's
	49	machine.
	50	.IP 6)
	51	A null terminated user name of at most 16 characters
	52	is retrieved on the initial socket. This user name
	53	is interpreted as the user identity on the
	54	.BR client 's
	55	machine.
	56	.IP 7)
	57	A null terminated command to be passed to a
	58	shell is retrieved on the initial socket. The length of
	59	the command is limited by the upper bound on the size of
	60	the system's argument list.
	61	.IP 8)
	62	.I Rshd
	63	then validates the user according to the following steps.
	64	The remote user name is looked up in the password file
65	and a
66	.I chdir
67	is performed to the user's home directory. If either
68	the lookup or
69	.I chdir
70	fail, the connection is terminated.
71	If the user is not the super-user, (user id 0), the file
72	.I /etc/hosts.equiv
73	is consulted for a list of hosts considered ``equivalent''.
74	If the client's host name is present in this file, the
75	authentication is considered successful. If the lookup
76	fails, or the user is the super-user, then the file
77	.I .rhosts
78	in the home directory of the remote user is checked for
79	the machine name and identity of the user on the client's
80	machine. If this lookup fails, the connection is terminated.
81	.IP 9)
82	A null byte is returned on the connection associated
83	with the
84	.B stderr
85	and the command line is passed to the normal login
86	shell of the user. The
87	shell inherits the network connections established
88	by
89	.IR rshd .
90	.SH DIAGNOSTICS
91	All diagnostic messages are returned on the connection
92	associated with the
93	.BR stderr ,
94	after which any network connections are closed.
95	An error is indicated by a leading byte with a value of
96	1 (0 is returned in step 9 above upon successful completion
97	of all the steps prior to the command execution).
98	.PP
99	.B ``locuser too long''
100	.br
101	The name of the user on the client's machine is
102	longer than 16 characters.
103	.PP
104	.B ``remuser too long''
105	.br
106	The name of the user on the remote machine is
107	longer than 16 characters.
108	.PP
109	.B ``command too long ''
110	.br
111	The command line passed exceeds the size of the argument
112	list (as configured into the system).
113	.PP
114	.B ``Hostname for your address unknown.''
115	.br
116	No entry in the host name database existed for
117	the client's machine.
118	.PP
119	.B ``Login incorrect.''
120	.br
121	No password file entry for the user name existed.
122	.PP
123	.B ``No remote directory.''
124	.br
125	The
126	.I chdir
127	command to the home directory failed.
128	.PP
129	.B ``Permission denied.''
130	.br
131	The authentication procedure described above failed.
132	.PP
133	.B ``Can't make pipe.''
134	.br
135	The pipe needed for the
136	.BR stderr ,
137	wasn't created.
138	.PP
139	.B ``Try again.''
140	.br
141	A
142	.I fork
143	by the server failed.
144	.PP
145	.B ``/bin/sh: ...''
146	.br
147	The user's login shell could not be started.
148	.SH SEE ALSO
149	rsh(1C),
150	rcmd(3X)
151	.SH BUGS
152	The authentication procedure used here assumes the integrity
153	of each client machine and the connecting medium. This is
154	insecure, but is useful in an ``open'' environment.
155	.PP
156	A facility to allow all data exchanges to be encrypted should be
157	present.