rshd(1M) — sysv — mips UMIPS RISC/os 4.52



RSHD(1M-SysV)       RISC/os Reference Manual        RSHD(1M-SysV)



NAME
     rshd - remote shell server

SYNOPSIS
     /etc/rshd

DESCRIPTION
     rshd is the server for the rcmd(3N) routine and, conse-
     quently, for the rsh(1C) program.  The server provides
     remote execution facilities with authentication based on
     privileged port numbers from trusted hosts.

     rshd listens for service requests at the port indicated in
     the ``cmd'' service specification; see services(4). When a
     service request is received the following protocol is ini-
     tiated:

     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 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 (see
          gethostbyname(3N), hosts(4) and named(8)).  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.



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     8)   rshd then validates the user according to the following
          steps.  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 either the lookup or chdir
          fail, the connection is terminated.  If the user is not
          the super-user, (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 authentication is considered success-
          ful.  If the lookup fails, or the user is the super-
          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.

     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 esta-
          blished by rshd.

DIAGNOSTICS
     Except for the last one listed below, all diagnostic mes-
     sages 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''
          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 argu-
          ment list (as configured into the system).

     ``Login incorrect.''
          No password file entry for the user name 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.




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     ``Try again.''
          A fork by the server failed.

     ``<shellname>: ...''
          The user's login shell could not be started.  This mes-
          sage is returned on the connection associated with the
          stderr, and is not preceded by a flag byte.

SEE ALSO
     rsh(1C) in the User's Reference Manual.
     rcmd(3N) in the Programmer's Reference Manual.

ERRORS
     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.

     A facility to allow all data exchanges to be encrypted
     should be present.

     A more extensible protocol should be used.


































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