_O_n_l_i_n_e _M_a_n_u_a_l        System Manager Commands             rshd(8c)



NNNNAAAAMMMMEEEE
     rshd - remote shell server

SSSSYYYYNNNNTTTTAAAAXXXX
     ////eeeettttcccc////rrrrsssshhhhdddd

DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
     _R_s_h_d is the server for the _r_c_m_d(3x) routine and, conse-
     quently, for the _r_s_h(1c) program.  The server provides
     remote execution facilities with authentication based on
     privileged port numbers from trusted hosts.

     _R_s_h_d listens for service requests at the port indicated in
     the ``cmd'' service specification; see _s_e_r_v_i_c_e_s(5).  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 ssssttttddddeeeerrrrrrrr.  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
          _g_e_t_h_o_s_t_b_y_a_d_d_r(3n), _h_o_s_t_s(5) and _n_a_m_e_d(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 cccclllliiiieeeennnntttt'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 sssseeeerrrrvvvveeeerrrr'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.

     8)   _R_s_h_d then validates the user according to the following
          steps.  The local (server-end) user name is looked up
          in the password file and a _c_h_d_i_r is performed to the
          user's home directory.  If either the lookup or _c_h_d_i_r
          fail, the connection is terminated.  If the user is not
          the super-user, (user id 0), the file /_e_t_c/_h_o_s_t_s._e_q_u_i_v






          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 ._r_h_o_s_t_s 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 _r_s_h_d.

DDDDIIIIAAAAGGGGNNNNOOOOSSSSTTTTIIIICCCCSSSS
     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).

     ````````llllooooccccuuuusssseeeerrrr ttttoooooooo lllloooonnnngggg''''''''
     The name of the user on the client's machine is longer than
     16 characters.

     ````````rrrreeeemmmmuuuusssseeeerrrr ttttoooooooo lllloooonnnngggg''''''''
     The name of the user on the remote machine is longer than 16
     characters.

     ````````ccccoooommmmmmmmaaaannnndddd ttttoooooooo lllloooonnnngggg ''''''''
     The command line passed exceeds the size of the argument
     list (as configured into the system).

     ````````LLLLooooggggiiiinnnn iiiinnnnccccoooorrrrrrrreeeecccctttt....''''''''
     No password file entry for the user name existed.

     ````````NNNNoooo rrrreeeemmmmooootttteeee ddddiiiirrrreeeeccccttttoooorrrryyyy....''''''''
     The _c_h_d_i_r command to the home directory failed.

     ````````PPPPeeeerrrrmmmmiiiissssssssiiiioooonnnn ddddeeeennnniiiieeeedddd....''''''''
     The authentication procedure described above failed.

     ````````CCCCaaaannnn''''tttt mmmmaaaakkkkeeee ppppiiiippppeeee....''''''''
     The pipe needed for the ssssttttddddeeeerrrrrrrr, wasn't created.

     ````````TTTTrrrryyyy aaaaggggaaaaiiiinnnn....''''''''
     A _f_o_r_k by the server failed.

     ````````<<<<sssshhhheeeellllllllnnnnaaaammmmeeee>>>>:::: ............''''''''
     The user's login shell could not be started.  This message
     is returned on the connection associated with the ssssttttddddeeeerrrrrrrr,
     and is not preceded by a flag byte.

SSSSEEEEEEEE AAAALLLLSSSSOOOO
     User Commands(1): rsh
     Library Functions(3): rcmd

LLLLIIIIMMMMIIIITTTTAAAATTTTIIIIOOOONNNNSSSS
     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.

December 1989                      TX System Manager's Reference