RSHD(8c,C) AIX TCP/IP User's Guide RSHD(8c,C) ------------------------------------------------------------------------------- rshd PURPOSE Provides the server function for remote command execution. SYNTAX /etc/rshd --------| DESCRIPTION The rshd command is the server for the rcmd routine and, consequently, for the rsh program. The server provides remote execution facilities with verification based on privileged port numbers from trusted hosts. The rshd command listens for service requests at the port indicated in the cmd service specification (see "services"). 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 breaks the connection. 2. The server reads characters from the socket up to a null (\0) byte. The resultant 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 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. 4. The server checks the client's source address and requests the corresponding host name (refer to gethostbyaddr in the AIX Operating System Technical Reference, "hosts" and "named"). If the hostname cannot be determined, the dot-notation representation of the host address is used. 5. 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. 6. 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. 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. Processed October 29, 1990 RSHD(8c,C) 1 RSHD(8c,C) AIX TCP/IP User's Guide RSHD(8c,C) 8. The rshd command then validates the user according to the following steps. o The local (server-end) user name is looked up in the password file and a chdir is performed to the user's home directory. If the lookup fails, the connection is terminated. o If the user is not the superuser, (user ID 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 verification is considered successful. If the lookup fails, or the user is the superuser, 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. o If this lookup fails, the connection is terminated. 9. A null byte is returned on the initial socket and the command line is passed to the normal login shell of the user. The shell inherits the network connections established by rshd. Note: The verification procedure used here assumes the integrity of each client machine and the connecting medium. This is insecure, but is useful in an open environment. MESSAGES All diagnostic messages are returned on the initial socket, 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 execution of the login shell). locuser too long Explanation: The name of the user on the client's machine is longer than 16 characters. remuser too long Explanation: The name of the user on the remote machine is longer than 16 characters. command too long Explanation: The command line passed exceeds the size of the argument list (as configured into the system). login incorrect Explanation: No password file entry for the user name existed. Processed October 29, 1990 RSHD(8c,C) 2 RSHD(8c,C) AIX TCP/IP User's Guide RSHD(8c,C) no remote directory Explanation: The chdir command to the home directory failed. permission denied Explanation: The verification procedure described above failed. can't make pipe Explanation: The pipe needed for the stderr wasn't created. Try again Explanation: A fork by the server failed. FILES /etc/hosts.equiv /etc/services $HOME/.rhost RELATED INFORMATION In this book: "rsh, remsh" gethostbyaddr, refer to AIX Operating System Technical Reference Processed October 29, 1990 RSHD(8c,C) 3