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3 .\" Modified for Solaris to to add the Solaris stability classification,
4 .\" and to add a note about source availability.
5 .\"
6 .TH HOSTS_OPTIONS 4 "Sep 15, 2011"
7 .SH NAME
8 hosts_options \- host access control language extensions
9 .SH DESCRIPTION
10 This document describes optional extensions to the language described
11 in the hosts_access(4) document. The extensions are enabled at program
12 build time. For example, by editing the Makefile and turning on the
13 PROCESS_OPTIONS compile-time option.
14 .PP
15 The extensible language uses the following format:
16 .sp
17 daemon_list : client_list : option : option ...
18 .PP
19 The first two fields are described in the hosts_access(4) manual page.
20 The remainder of the rules is a list of zero or more options. Any ":"
21 characters within options should be protected with a backslash.
22 .PP
23 An option is of the form "keyword" or "keyword value". Options are
24 processed in the specified order. Some options are subjected to
25 %<letter> substitutions. For the sake of backwards compatibility with
26 earlier versions, an "=" is permitted between keyword and value.
27 .SH LOGGING
28 .IP "severity mail.info"
29 .IP "severity notice"
30 Change the severity level at which the event will be logged. Facility
31 names (such as mail) are optional, and are not supported on systems
32 with older syslog implementations. The severity option can be used
33 to emphasize or to ignore specific events.
34 .SH ACCESS CONTROL
35 .IP "allow"
36 .IP "deny"
37 Grant (deny) service. These options must appear at the end of a rule.
38 .PP
39 The \fIallow\fR and \fIdeny\fR keywords make it possible to keep all
40 access control rules within a single file, for example in the
41 \fIhosts.allow\fR file.
42 .sp
43 To permit access from specific hosts only:
44 .sp
45 .ne 2
46 ALL: .friendly.domain: ALLOW
47 ALL: ALL: DENY
48 .sp
49 To permit access from all hosts except a few trouble makers:
50 .sp
51 .ne 2
52 ALL: .bad.domain: DENY
53 ALL: ALL: ALLOW
54 .sp
55 Notice the leading dot on the domain name patterns.
56 .SH RUNNING OTHER COMMANDS
57 .IP "spawn shell_command"
58 Execute, in a child process, the specified shell command, after
59 performing the %<letter> expansions described in the hosts_access(4)
60 manual page. The command is executed with stdin, stdout and stderr
61 connected to the null device, so that it won\'t mess up the
62 conversation with the client host. Example:
63 .sp
64 .nf
65 spawn (/some/where/safe_finger -l @%h | /usr/ucb/mail root) &
66 .fi
67 .sp
68 executes, in a background child process, the shell command "safe_finger
69 -l @%h | mail root" after replacing %h by the name or address of the
70 remote host.
71 .sp
72 The example uses the "safe_finger" command instead of the regular
73 "finger" command, to limit possible damage from data sent by the finger
74 server. The "safe_finger" command is part of the daemon wrapper
75 package; it is a wrapper around the regular finger command that filters
76 the data sent by the remote host.
77 .IP "twist shell_command"
78 Replace the current process by an instance of the specified shell
79 command, after performing the %<letter> expansions described in the
80 hosts_access(4) manual page. Stdin, stdout and stderr are connected to
81 the client process. This option must appear at the end of a rule.
82 .sp
83 To send a customized bounce message to the client instead of
84 running the real ftp daemon:
85 .sp
86 .nf
87 in.ftpd : ... : twist /bin/echo 421 Some bounce message
88 .fi
89 .sp
90 For an alternative way to talk to client processes, see the
91 \fIbanners\fR option below.
92 .sp
93 To run /some/other/in.telnetd without polluting its command-line
94 array or its process environment:
95 .sp
96 .nf
97 in.telnetd : ... : twist PATH=/some/other; exec in.telnetd
98 .fi
99 .sp
100 Warning: in case of UDP services, do not twist to commands that use
101 the standard I/O or the read(2)/write(2) routines to communicate with
102 the client process; UDP requires other I/O primitives.
103 .SH NETWORK OPTIONS
104 .IP "keepalive"
105 Causes the server to periodically send a message to the client. The
106 connection is considered broken when the client does not respond. The
107 keepalive option can be useful when users turn off their machine while
108 it is still connected to a server. The keepalive option is not useful
109 for datagram (UDP) services.
110 .IP "linger number_of_seconds"
111 Specifies how long the kernel will try to deliver not-yet delivered
112 data after the server process closes a connection.
113 .SH USERNAME LOOKUP
114 .IP "rfc931 [ timeout_in_seconds ]"
115 Look up the client user name with the RFC 931 (TAP, IDENT, RFC 1413)
116 protocol. This option is silently ignored in case of services based on
117 transports other than TCP. It requires that the client system runs an
118 RFC 931 (IDENT, etc.) -compliant daemon, and may cause noticeable
119 delays with connections from non-UNIX clients. The timeout period is
120 optional. If no timeout is specified a compile-time defined default
121 value is taken.
122 .SH MISCELLANEOUS
123 .IP "banners /some/directory"
124 Look for a file in `/some/directory' with the same name as the daemon
125 process (for example in.telnetd for the telnet service), and copy its
126 contents to the client. Newline characters are replaced by
127 carriage-return newline, and %<letter> sequences are expanded (see
128 the hosts_access(4) manual page).
129 .sp
130 The tcp wrappers source code distribution provides a sample makefile
131 (Banners.Makefile) for convenient banner maintenance.
132 .sp
133 Warning: banners are supported for connection-oriented (TCP) network
134 services only.
135 .IP "nice [ number ]"
136 Change the nice value of the process (default 10). Specify a positive
137 value to spend more CPU resources on other processes.
138 .IP "setenv name value"
139 Place a (name, value) pair into the process environment. The value is
140 subjected to %<letter> expansions and may contain whitespace (but
141 leading and trailing blanks are stripped off).
142 .sp
143 Warning: many network daemons reset their environment before spawning a
144 login or shell process.
145 .IP "umask 022"
146 Like the umask command that is built into the shell. An umask of 022
147 prevents the creation of files with group and world write permission.
148 The umask argument should be an octal number.
149 .IP "user nobody"
150 .IP "user nobody.kmem"
151 Assume the privileges of the "nobody" userid (or user "nobody", group
152 "kmem"). The first form is useful with inetd implementations that run
153 all services with root privilege. The second form is useful for
154 services that need special group privileges only.
155 .SH DIAGNOSTICS
156 When a syntax error is found in an access control rule, the error
157 is reported to the syslog daemon; further options will be ignored,
158 and service is denied.
159 .SH SEE ALSO
160 hosts_access(4), the default access control language
161 .SH AUTHOR
162 .na
163 .nf
164 Wietse Venema (wietse@wzv.win.tue.nl)
165 Department of Mathematics and Computing Science
166 Eindhoven University of Technology
167 Den Dolech 2, P.O. Box 513,
168 5600 MB Eindhoven, The Netherlands
169 \" @(#) hosts_options.5 1.10 94/12/28 17:42:28
170 .\" Begin Sun update
171 .SH ATTRIBUTES
172 See
173 .BR attributes (5)
174 for descriptions of the following attributes:
175 .sp
176 .TS
177 box;
178 c | c
179 l | l .
180 ATTRIBUTE TYPE ATTRIBUTE VALUE
181 =
182 Interface Stability Committed
183 .TE
184 .\" End Sun update