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