rshd(8c) — AIX PS/2 1.2.1



RSHD(8c,C)                  AIX TCP/IP User's Guide                  RSHD(8c,C)



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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

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