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HOSTS_OPTIONS(5)	      File Formats Manual	      HOSTS_OPTIONS(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 pro-
       cessed  in the specified	order. Some options are	subjected to %<letter>
       substitutions. For the sake of  backwards  compatibility	 with  earlier
       versions, an "="	is permitted between keyword and value.


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


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

       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 regu-
	      lar "finger" command, to limit possible damage from data sent by
	      the finger server. The "safe_finger" command is part of the dae-
	      mon 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 daemon:

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

	      For an alternative way to	talk to	client processes, see the ban-
	      ners 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	commu-
	      nicate with the client process; UDP requires  other  I/O	primi-

	      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	deliv-
	      ered 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 ser-
	      vices 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 spec-
	      ified 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.Makefile) 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 implementa-
	      tions that run all services with root privilege. The second form
	      is useful	for services that need special group privileges	only.

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

       hosts_access(5),	the default access control language

       Wietse Venema (
       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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