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32 .\" @(#)rshd.8 8.1 (Berkeley) 6/4/93
40 .Nd remote shell server
50 routine and, consequently, for the
52 program. The server provides remote execution facilities
53 with authentication based on privileged port numbers from trusted hosts.
58 listens for service requests at the port indicated in
61 service specification; see
63 When a service request is received the following protocol
67 The server checks the client's source port.
68 If the port is not in the range 512-1023, the server
69 aborts the connection.
71 The server reads characters from the socket up
74 (`\e0') byte. The resultant string is
79 If the number received in step 2 is non-zero,
80 it is interpreted as the port number of a secondary
81 stream to be used for the
83 A second connection is then created to the specified
84 port on the client's machine. The source port of this
85 second connection is also in the range 512-1023.
87 The server checks the client's source address
88 and requests the corresponding host name (see
93 If the hostname cannot be determined or the hostname and address do
94 not match after verification,
95 the dot-notation representation of the host address is used.
97 A null terminated user name of at most 16 characters
98 is retrieved on the initial socket. This user name
99 is interpreted as the user identity on the
103 A null terminated user name of at most 16 characters
104 is retrieved on the initial socket. This user name
105 is interpreted as a user identity to use on the
109 A null terminated command to be passed to a
110 shell is retrieved on the initial socket. The length of
111 the command is limited by the upper bound on the size of
112 the system's argument list.
115 then validates the user using
121 file found in the user's home directory. The
125 from doing any validation based on the user's
128 unless the user is the superuser.
132 exists and the user is not the superuser,
133 the connection is closed.
134 The name of the nologin file may be overridden
135 using the nologin capability in
137 according to the local user's login class,
138 which may also be used to restrict
141 login time (times.allow and times.deny capabilities)
142 and remote host (hosts.allow and hosts.deny capabilities).
146 byte is returned on the initial socket
147 and the command line is passed to the normal login
148 shell of the user. The
149 shell inherits the network connections established
154 Transport-level keepalive messages are enabled unless the
157 The use of keepalive messages allows sessions to be timed out
158 if the client crashes or becomes unreachable.
162 option sets the TCP_NODELAY socket option which improves
163 performance of small back-to-back
164 writes at the expense of additional network traffic.
168 option causes all successful accesses to be logged to
174 Except for the last one listed below,
175 all diagnostic messages
176 are returned on the initial socket,
177 after which any network connections are closed.
178 An error is indicated by a leading byte with a value of
179 1 (0 is returned in step 10 above upon successful completion
180 of all the steps prior to the execution of the login shell).
181 .Bl -tag -width indent
182 .It Sy Locuser too long.
183 The name of the user on the client's machine is
184 longer than 16 characters.
185 .It Sy Ruser too long.
186 The name of the user on the remote machine is
187 longer than 16 characters.
188 .It Sy Command too long.
189 The command line passed exceeds the size of the argument
190 list (as configured into the system).
191 .It Sy Login incorrect.
192 No password file entry for the user name existed
193 or the authentication procedure described above failed.
194 .It Sy Remote directory.
197 function to the home directory failed.
198 .It Sy Logins not available right now.
200 was attempted outside the allowed hours defined in
202 for the local user's login class.
203 .It Sy Can't make pipe.
204 The pipe needed for the
207 .It Sy Can't fork; try again.
210 by the server failed.
211 .It Sy <shellname>: ...
212 The user's login shell could not be started. This message is returned
213 on the connection associated with the
215 and is not preceded by a flag byte.
220 .Xr gethostbyaddr 3 ,
233 .Bl -tag -width /etc/hosts -compact
235 .It Pa /etc/hosts.equiv
236 .It Pa /etc/login.conf
238 .It Pa Ev $HOME /.rhosts
240 .It Pa /var/run/nologin
243 The authentication procedure used here assumes the integrity
244 of each client machine and the connecting medium. This is
245 insecure, but is useful in an
249 A facility to allow all data exchanges to be encrypted should be
252 A more extensible protocol (such as Telnet) should be used.
254 IPv6 support was added by WIDE/KAME project.