RSHD(8)
NAME
rshd − remote Shell server
USAGE
/etc/rshd
DESCRIPTION
Rshd is the server for the rcmd(3X) routine and, consequently, for the rsh(1) program. The server provides remote execution facilities with authentication based on privileged port numbers.
Rshd listens for service requests at the port indicated in the “cmd” service specification. 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 0-1023, the server aborts the connection.
2)The server reads characters from the socket up to a null (‘\0’) byte. The resulting string is interpreted as an ASCII number, base 10.
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 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.
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 database, the server aborts the connection.
5)The server retrieves a null terminated username (maximum 16 characters) on the initial socket. This name is interpreted as a user account to be used on the server’s machine.
6)The server retrieves a null terminated username (maximum 16 characters) on the initial socket. This name is interpreted as a user account to be used on the client’s machine.
7)The server interprets the next string, up to a null character, as a command to be passed to the Shell. The upper bound on the size of the system’s argument list limits the length of the command.
8)Rshd then validates the user according to the following steps. The remote username is looked up in the password file and a chdir is performed to the user’s home directory. If either the lookup or chdir fail, the connection is terminated. If the user is not the super-user (user ID zero), 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 searched for the machine name and identity of the user on the client’s machine. If this lookup fails, the connection is terminated.
9)A null byte is returned on the connection associated with the stderr and the command line is passed to the normal log-in Shell of the user. The Shell inherits the network connections established by rshd.
NOTES
The authentication procedure used here assumes the integrity of each client machine and the connecting medium.
DIAGNOSTICS
All 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 (zero is returned in step 9 above 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 username existed.
No remote directory.
The chdir command to the home directory failed.
Permission denied.
The authentication procedure described above failed.
Can’t make pipe.
The pipe needed for the stderr wasn’t created.
Try again.
A fork by the server failed.
/bin/sh: ...
The user’s log-in Shell could not be started.