HOSTS_OPTIONS(5)          FreeBSD File Formats 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 implementations. 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:

        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 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 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.

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 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 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

                                                              HOSTS_OPTIONS(5)