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