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HOSTS_OPTIONS(5)					      HOSTS_OPTIONS(5)

NAME
       hosts_options - host access control language extensions

DESCRIPTION
       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.

LOGGING
       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  sup‐
	      ported  on systems with older syslog implementations. The sever‐
	      ity option can be	 used  to  emphasize  or  to  ignore  specific
	      events.

ACCESS CONTROL
       allow

       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
	  ALL: ALL: DENY

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

	  ALL: .bad.domain: DENY
	  ALL: ALL: ALLOW

       Notice the leading dot on the domain name patterns.

RUNNING OTHER COMMANDS
       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‐
	      tives.

NETWORK OPTIONS
       keepalive
	      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.

USERNAME LOOKUP
       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.

MISCELLANEOUS
       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.

DIAGNOSTICS
       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.

SEE ALSO
       hosts_access(5), the default access control language

AUTHOR
       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

							      HOSTS_OPTIONS(5)
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