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

NAME

       rexecd - remote execution server

SYNOPSIS

       /usr/libexec/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(5).  When a  service  request
       is received the following protocol is initiated:

       1)     The  server reads characters from the socket up to a null (`') 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 direc-
	      tory, and establishes the user and group protections of the user.  If any of these steps fail the connection is aborted with a diag-
	      nostic 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 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(3)

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					 November 16, 1996							 REXECD(8)