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 %<let-
       ter> substitutions.  For the sake of backwards compatibility with  ear-
       lier 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.  Exam-
              ple:

                 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
              daemon  wrapper package; it is a wrapper around the regular fin-
              ger 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
              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  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(3) 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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