REXECD(1M)          RISC/os Reference Manual           REXECD(1M)



NAME
     rexecd - remote execution server

SYNOPSIS
     /etc/rexecd

DESCRIPTION
     rexecd is the server for the rexec(3) routine.  The server
     provides remote execution facilities with authentication
     based on user names and passwords.

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

     1)   The server reads characters from the socket up to a
          null (`\0') byte.  The resultant string is interpreted
          as an ASCII number, base 10.

     2)   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.

     3)   A null terminated user name of at most 16 characters is
          retrieved on the initial socket.

     4)   A null terminated, unencrypted password of at most 16
          characters is retrieved on the initial socket.

     5)   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.

     6)   rexecd then validates the user as is done at login time
          and, if the authentication was successful, changes to
          the user's home directory, and establishes the user and
          group protections of the user.  If any of these steps
          fail the connection is aborted with a diagnostic mes-
          sage returned.

     7)   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 rexecd.

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



                        Printed 11/19/92                   Page 1

REXECD(1M)          RISC/os Reference Manual           REXECD(1M)



     leading byte with a value of 1 (0 is returned in step 7
     above upon successful completion of all the steps prior to
     the command execution).

     ``username too long''
          The name is longer than 16 characters.

     ``password too long''
          The password 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.

     ``Password incorrect.''
          The wrong was password supplied.

     ``No remote directory.''
          The chdir command to the home directory failed.

     ``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
     rexec(3)

ERRORS
     Indicating ``Login incorrect'' as opposed to ``Password
     incorrect'' is a security breach which allows people to
     probe a system for users with null passwords.

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














 Page 2                 Printed 11/19/92