4.4BSD/usr/share/man/cat8/rexecd.0

REXECD(8)                 BSD System Manager's Manual                REXECD(8)

NNAAMMEE
     rreexxeeccdd - remote execution server

SSYYNNOOPPSSIISS
     rreexxeeccdd

DDEESSCCRRIIPPTTIIOONN
     RReexxeeccdd is the server for the rexec(3) routine.  The server provides re-
     mote execution facilities with authentication based on user names and
     passwords.

     RReexxeeccdd listens for service requests at the port indicated in the ``exec''
     service specification; see services(5).  When a service request is re-
     ceived the following protocol is initiated:

     1.   The server reads characters from the socket up to a NUL (`\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 _s_t_d_e_r_r. A
          second connection is then created to the specified port on the
          client's machine.

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

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

     5.   A NUL 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.   RReexxeeccdd 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 NUL 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 rreexxeeccdd.

DDIIAAGGNNOOSSTTIICCSS
     Except for the last one listed below, all diagnostic messages are re-
     turned 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 pri-
     or to the command execution).

     uusseerrnnaammee ttoooo lloonngg
             The name is longer than 16 characters.

     ppaasssswwoorrdd ttoooo lloonngg
             The password is longer than 16 characters.

     ccoommmmaanndd ttoooo lloonngg
             The command line passed exceeds the size of the argument list (as
             configured into the system).

     LLooggiinn iinnccoorrrreecctt..


             No password file entry for the user name existed.

     PPaasssswwoorrdd iinnccoorrrreecctt..
             The wrong was password supplied.

     NNoo rreemmoottee ddiirreeccttoorryy..
             The chdir command to the home directory failed.

     TTrryy aaggaaiinn..
             A fork by the server failed.

     <<sshheellllnnaammee>>:: ......
             The user's login shell could not be started.  This message is re-
             turned on the connection associated with the _s_t_d_e_r_r, and is not
             preceded by a flag byte.

SSEEEE AALLSSOO
     rexec(3)

BBUUGGSS
     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.

HHIISSTTOORRYY
     The rreexxeeccdd command appeared in 4.2BSD.

4.2 Berkeley Distribution        June 4, 1993                                2