REXECD(1M)                                             REXECD(1M)



     NAME
          rexecd - remote execution server

     SYNOPSIS
          /usr/etc/rexecd

     DESCRIPTION
          Rexecd is the server for the rexec(3N) 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
          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)   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
               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.

     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



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     REXECD(1M)                                             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 argument
          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 message
          is returned on the connection associated with the stderr,
          and is not preceded by a flag byte.

     SEE ALSO
          rexec(3N)

     BUGS
          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.

     ORIGIN
          U.C. Berkeley, with changes from Silicon Graphics, Inc.











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