173 lines
6.5 KiB
Groff
173 lines
6.5 KiB
Groff
.TH HOSTS_OPTIONS 5
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.SH NAME
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hosts_options \- host access control language extensions
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.SH DESCRIPTION
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This document describes optional extensions to the language described
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in the hosts_access(5) document. The extensions are enabled at program
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build time. For example, by editing the Makefile and turning on the
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PROCESS_OPTIONS compile-time option.
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.PP
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The extensible language uses the following format:
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.sp
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.ti +3
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daemon_list : client_list : option : option ...
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.PP
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The first two fields are described in the hosts_access(5) manual page.
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The remainder of the rules is a list of zero or more options. Any ":"
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characters within options should be protected with a backslash.
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.PP
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An option is of the form "keyword" or "keyword value". Options are
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processed in the specified order. Some options are subjected to
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%<letter> substitutions. For the sake of backwards compatibility with
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earlier versions, an "=" is permitted between keyword and value.
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.SH LOGGING
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.IP "severity mail.info"
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.IP "severity notice"
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Change the severity level at which the event will be logged. Facility
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names (such as mail) are optional, and are not supported on systems
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with older syslog implementations. The severity option can be used
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to emphasize or to ignore specific events.
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.SH ACCESS CONTROL
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.IP "allow"
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.IP "deny"
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Grant (deny) service. These options must appear at the end of a rule.
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.PP
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The \fIallow\fR and \fIdeny\fR keywords make it possible to keep all
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access control rules within a single file, for example in the
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\fIhosts.allow\fR file.
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.sp
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To permit access from specific hosts only:
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.sp
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.ne 2
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.ti +3
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ALL: .friendly.domain: ALLOW
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.ti +3
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ALL: ALL: DENY
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.sp
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To permit access from all hosts except a few trouble makers:
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.sp
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.ne 2
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.ti +3
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ALL: .bad.domain: DENY
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.ti +3
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ALL: ALL: ALLOW
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.sp
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Notice the leading dot on the domain name patterns.
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.SH RUNNING OTHER COMMANDS
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.IP "spawn shell_command"
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Execute, in a child process, the specified shell command, after
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performing the %<letter> expansions described in the hosts_access(5)
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manual page. The command is executed with stdin, stdout and stderr
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connected to the null device, so that it won\'t mess up the
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conversation with the client host. Example:
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.sp
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.nf
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.ti +3
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spawn (/some/where/safe_finger -l @%h | /usr/ucb/mail root) &
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.fi
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.sp
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executes, in a background child process, the shell command "safe_finger
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-l @%h | mail root" after replacing %h by the name or address of the
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remote host.
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.sp
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The example uses the "safe_finger" command instead of the regular
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"finger" command, to limit possible damage from data sent by the finger
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server. The "safe_finger" command is part of the daemon wrapper
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package; it is a wrapper around the regular finger command that filters
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the data sent by the remote host.
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.IP "twist shell_command"
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Replace the current process by an instance of the specified shell
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command, after performing the %<letter> expansions described in the
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hosts_access(5) manual page. Stdin, stdout and stderr are connected to
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the client process. This option must appear at the end of a rule.
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.sp
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To send a customized bounce message to the client instead of
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running the real ftp daemon:
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.sp
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.nf
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.ti +3
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in.ftpd : ... : twist /bin/echo 421 Some bounce message
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.fi
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.sp
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For an alternative way to talk to client processes, see the
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\fIbanners\fR option below.
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.sp
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To run /some/other/in.telnetd without polluting its command-line
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array or its process environment:
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.sp
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.nf
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.ti +3
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in.telnetd : ... : twist PATH=/some/other; exec in.telnetd
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.fi
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.sp
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Warning: in case of UDP services, do not twist to commands that use
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the standard I/O or the read(2)/write(2) routines to communicate with
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the client process; UDP requires other I/O primitives.
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.SH NETWORK OPTIONS
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.IP "keepalive"
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Causes the server to periodically send a message to the client. The
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connection is considered broken when the client does not respond. The
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keepalive option can be useful when users turn off their machine while
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it is still connected to a server. The keepalive option is not useful
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for datagram (UDP) services.
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.IP "linger number_of_seconds"
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Specifies how long the kernel will try to deliver not-yet delivered
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data after the server process closes a connection.
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.SH USERNAME LOOKUP
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.IP "rfc931 [ timeout_in_seconds ]"
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Look up the client user name with the RFC 931 (TAP, IDENT, RFC 1413)
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protocol. This option is silently ignored in case of services based on
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transports other than TCP. It requires that the client system runs an
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RFC 931 (IDENT, etc.) -compliant daemon, and may cause noticeable
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delays with connections from non-UNIX clients. The timeout period is
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optional. If no timeout is specified a compile-time defined default
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value is taken.
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.SH MISCELLANEOUS
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.IP "banners /some/directory"
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Look for a file in `/some/directory' with the same name as the daemon
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process (for example in.telnetd for the telnet service), and copy its
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contents to the client. Newline characters are replaced by
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carriage-return newline, and %<letter> sequences are expanded (see
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the hosts_access(5) manual page).
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.sp
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The tcp wrappers source code distribution provides a sample makefile
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(Banners.Makefile) for convenient banner maintenance.
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.sp
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Warning: banners are supported for connection-oriented (TCP) network
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services only.
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.IP "nice [ number ]"
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Change the nice value of the process (default 10). Specify a positive
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value to spend more CPU resources on other processes.
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.IP "setenv name value"
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Place a (name, value) pair into the process environment. The value is
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subjected to %<letter> expansions and may contain whitespace (but
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leading and trailing blanks are stripped off).
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.sp
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Warning: many network daemons reset their environment before spawning a
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login or shell process.
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.IP "umask 022"
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Like the umask command that is built into the shell. An umask of 022
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prevents the creation of files with group and world write permission.
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The umask argument should be an octal number.
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.IP "user nobody"
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.IP "user nobody.kmem"
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Assume the privileges of the "nobody" userid (or user "nobody", group
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"kmem"). The first form is useful with inetd implementations that run
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all services with root privilege. The second form is useful for
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services that need special group privileges only.
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.SH DIAGNOSTICS
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When a syntax error is found in an access control rule, the error
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is reported to the syslog daemon; further options will be ignored,
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and service is denied.
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.SH SEE ALSO
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hosts_access(5), the default access control language
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.SH AUTHOR
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.na
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.nf
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Wietse Venema (wietse@wzv.win.tue.nl)
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Department of Mathematics and Computing Science
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Eindhoven University of Technology
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Den Dolech 2, P.O. Box 513,
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5600 MB Eindhoven, The Netherlands
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\" @(#) hosts_options.5 1.10 94/12/28 17:42:28
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