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BSD 2.11 - man page for rexecd (bsd section 8)

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REXECD(8)										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 specifi-
       cation;	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  resul-
	      tant 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  cre-
	      ated 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 estab-
	      lished 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 lead-
       ing 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 sys-
       tem).

       ``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)
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