4.3BSD - /usr/man/cat8/rexecd.0

REXECD(8C)                                                          REXECD(8C)


NAME
       rexecd - remote execution server

SYNOPSIS
       /etc/rexecd

DESCRIPTION
       Rexecd  is  the  server for the rexec(3X) 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(5).   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 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  con‐
       figured 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(3X)

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.


4.2 Berkeley Distribution         May 9, 1986                       REXECD(8C)