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RedHat 9 (Linux i386) - man page for hosts_options (redhat section 5)

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       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 speci-
       fied 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 events.


       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(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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