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NetBSD 6.1.5 - man page for hosts_options (netbsd section 5)


       hosts_options - host access control language extensions

       This   document	 describes   optional	extensions  to	the  language  described  in  the
       hosts_access(5) document.  The extensions are enabled at program build time.  For example,
       by editing the Makefile and turning on the PROCESS_OPTIONS compile-time option.

       The extensible language uses the following format:

	  daemon_list : client_list : option : option ...

       The  first  two fields are described in the hosts_access(5) manual page.  The remainder of
       the rules is a list of zero or more options.  Any ":" characters within options should  be
       protected with a backslash.

       An option is of the form "keyword" or "keyword value".  Options are processed in the spec-
       ified order.  Some options are subjected to %letter substitutions.  For the sake of  back-
       wards compatibility with earlier versions, an "=" is permitted between keyword and value.

       severity mail.info

       severity notice
	      Change  the severity level at which the event will be logged.  Facility names (such
	      as mail) are optional, and are not supported on systems with older syslog implemen-
	      tations.	 The  severity	option	can  be  used  to emphasize or to ignore specific


       deny   Grant (deny) service.  These options must appear at the end of a rule.

       The allow and deny keywords make it possible to keep all access	control  rules	within	a
       single file, for example in the hosts.allow file.

       To permit access from specific hosts only:

	  ALL: .friendly.domain: ALLOW

       To permit access from all hosts except a few trouble makers:

	  ALL: .bad.domain: DENY

       Notice the leading dot on the domain name patterns.

       spawn shell_command
	      Execute,	in  a  child  process,	the specified shell command, after performing the
	      %letter expansions described in the hosts_access(5) manual page.	 The  command  is
	      executed	with  stdin,  stdout  and stderr connected to the null device, so that it
	      won't mess up the conversation with the client host.  Example:

		 spawn (/some/where/safe_finger -l @%h | /usr/ucb/mail root)

	      executes, in a background child process, the shell command "safe_finger  -l  @%h	|
	      mail root" after replacing %h by the name or address of the remote host.

	      The example uses the "safe_finger" command instead of the regular "finger" command,
	      to limit possible damage from data sent by the finger  server.   The  "safe_finger"
	      command  is  part of the daemon wrapper package; it is a wrapper around the regular
	      finger command that filters the data sent by the remote host.

       twist shell_command
	      Replace the current process by an instance of the specified  shell  command,  after
	      performing  the  %letter	expansions  described in the hosts_access(5) manual page.
	      Stdin, stdout and stderr are connected to the client  process.   This  option  must
	      appear at the end of a rule.

	      To  send	a customized bounce message to the client instead of running the real ftp

		 in.ftpd : ... : twist /bin/echo 421 Some bounce message

	      For an alternative way to talk to client processes, see the banners option below.

	      To run /some/other/in.telnetd without  polluting	its  command-line  array  or  its
	      process environment:

		 in.telnetd : ... : twist PATH=/some/other; exec in.telnetd

	      Warning:	 in  case of UDP services, do not twist to commands that use the standard
	      I/O or the read(2)/write(2) routines to communicate with the  client  process;  UDP
	      requires other I/O primitives.

	      Causes  the server to periodically send a message to the client.	The connection is
	      considered broken when the client does not respond.  The keepalive  option  can  be
	      useful  when  users turn off their machine while it is still connected to a server.
	      The keepalive option is not useful for datagram (UDP) services.

       linger number_of_seconds
	      Specifies how long the kernel will try to deliver not-yet delivered data after  the
	      server process closes a connection.

       rfc931 [ timeout_in_seconds ]
	      Look  up	the  client  user  name with the RFC 931 (TAP, IDENT, RFC 1413) protocol.
	      This option is silently ignored in case of services based on transports other  than
	      TCP.   It requires that the client system runs an RFC 931 (IDENT, etc.)  -compliant
	      daemon, and may cause noticeable delays with  connections  from  non-UNIX  clients.
	      The  timeout period is optional.	If no timeout is specified a compile-time defined
	      default value is taken.

       banners /some/directory
	      Look for a file in `/some/directory' with the same name as the daemon process  (for
	      example  in.telnetd  for	the telnet service), and copy its contents to the client.
	      Newline characters are replaced by carriage-return newline, and  %letter	sequences
	      are expanded (see the hosts_access(5) manual page).

	      The tcp wrappers source code distribution provides a sample makefile (Banners.Make-
	      file) for convenient banner maintenance.

	      Warning: banners are supported for connection-oriented (TCP) network services only.

       nice [ number ]
	      Change the nice value of the process (default 10).  Specify  a  positive	value  to
	      spend more CPU resources on other processes.

       setenv name value
	      Place a (name, value) pair into the process environment.	The value is subjected to
	      %letter expansions and may contain whitespace (but leading and trailing blanks  are
	      stripped off).

	      Warning:	many  network  daemons reset their environment before spawning a login or
	      shell process.

       umask 022
	      Like the umask command that is built into the shell.  An umask of 022 prevents  the
	      creation of files with group and world write permission.	The umask argument should
	      be an octal number.

       user nobody

       user nobody.kmem
	      Assume the privileges of the "nobody" userid (or user "nobody", group "kmem").  The
	      first  form  is  useful  with inetd implementations that run all services with root
	      privilege.  The second form is useful for services that need special  group  privi-
	      leges only.

       When  a syntax error is found in an access control rule, the error is reported to the sys-
       log daemon; further options will be ignored, and service is denied.

       hosts_access(3) hosts_access(5), the default access control language

       Wietse Venema (wietse@wzv.win.tue.nl)
       Department of Mathematics and Computing Science
       Eindhoven University of Technology
       Den Dolech 2, P.O. Box 513,
       5600 MB Eindhoven, The Netherlands


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