REXECD(ADMN)                       UNIX System V



     Name
          rexecd - remote execution server


     Syntax
          /etc/rexecd


     Description
          rexecd is the  server  for  the  rexec(SLIB)  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(SFF).  When a
          service request  is  received,  the  following  protocol  is
          initiated:

          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)   Then, rexecd 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
               message 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
               established by rexecd.

          rexecd is started by the super-server inetd,  and  therefore
          must   have   an   entry   in   inetd's  configuration  file
          /etc/inetd.conf.


     Diagnostics
          Except  for  the  last  one  listed  below,  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 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
                    argument list (as configured into the system).

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

          ``Password incorrect.''
                    The wrong password was 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
                    message  is  returned on the connection associated
                    with the stderr, and is not  preceded  by  a  flag
                    byte.


     See Also
          rexec(SLIB), inetd(ADMN), inetd.conf(SFF), services(SFF).


     Notes
          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.


     (printed 8/17/89)                                  REXECD(ADMN)