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 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>  expan-
              sions 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) rou-
              tines 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 connec-
              tion.

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 tel-
              net 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  spe-
              cial 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 (wietseATwzv.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)