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hosts_options (5)
  • >> hosts_options (5) ( Solaris man: Форматы файлов )
  • hosts_options (5) ( FreeBSD man: Форматы файлов )
  • hosts_options (5) ( Linux man: Форматы файлов )
         hosts_options - host access control language extensions
         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
         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.
         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.
         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.
         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
              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.
              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
         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
         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).
              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.
         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.
         hosts_access(5), the default access control language
         Wietse Venema (
         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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