HOSTS_OPTIONS(5)    UNIX Programmer's Manual	 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 processed 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 supported on systems with older syslog imple-
	  mentations. The severity 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:


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	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 com-
	  mand, after performing the %<letter> expansions
	  described in the hosts_access(5) manual page.  The com-
	  mand is executed with stdin, stdout and stderr con-
	  nected 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 com-
	  mand "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 daemon:

	     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 com-
	  mands 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.


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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 delivered 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 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.

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 new-
	  line, 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 environ-
	  ment. The value is subjected to %<letter> expansions
	  and may contain whitespace (but leading and trailing
	  blanks are stripped off).


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	  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 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


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