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1.1 root 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.
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