rshd(1Mtcp)
rshd --
remote shell server
Synopsis
in.rshd host.port
Description
The rshd command is the server for the
rcp(1tcp)
and
rsh(1tcp)
programs.
The server provides remote execution facilities
with authentication based on privileged port numbers.
Files
/etc/hosts.equiv-
Diagnostics
The following diagnostic messages are returned on the connection
associated with the 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 below upon successful completion
of all the steps prior to the command execution).
locuser too long
-
The name of the user on the client's machine is
longer than 16 characters.
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).
Hostname for your address unknown.
-
No entry in the host name database existed for
the client's machine.
Login incorrect.
-
No password file entry for the user name existed.
Permission denied.
-
The authentication procedure described below failed.
Can't make pipe.
-
The pipe needed for the stderr was not created.
Try again.
-
A fork by the server failed.
Usage
rshd is invoked by
inetd(1Mtcp)
each time a shell service is requested, and executes the
following protocol:
-
The server checks the client's source port.
If the port is not in the range
0-1023, the server
aborts the connection.
The clients host address (in hex)
and port number (in decimal) are the argument passed to rshd.
-
The server reads characters from the socket up
to a null (\0) byte.
The resultant string is
interpreted as an
ASCII
number, base 10.
-
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 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.
-
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
hosts(4tcp)),
the server aborts the connection.
-
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.
-
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.
-
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.
-
rshd then validates the user according to the following steps.
The remote user name is looked up in the password file and a
chdir is performed to the user's home directory.
If the lookup or
fails, the connection is terminated.
If the chdir fails, it does a chdir to / (root).
If the user is not root (UID is 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 a privileged 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.
-
A null byte is returned on the connection associated
with the stderr
and the command line is passed to the normal login
shell of the user.
The shell inherits the network connections established by rshd.
References
inetd(1Mtcp),
inetd.conf(4tcp),
rcp(1tcp),
rsh(1tcp)
Notices
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.
If a remote user does not have a
home directory, the root directory (/) becomes
the user's home directory.
A facility to allow all data exchanges
to be encrypted should be present.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004