1HOST.CONF(5) Linux System Administration HOST.CONF(5)
2
6 host.conf - resolver configuration file
7
9 The file /etc/host.conf contains configuration information specific to
10 the resolver library. It should contain one configuration keyword per
11 line, followed by appropriate configuration information. The keywords
12 recognized are trim, multi, nospoof, spoof, and reorder. These key‐
13 words are described below.
14 trim This keyword may be listed more than once. Each time it should
16 be followed by a list of domains, separated by colons (':'),
17 semicolons (';') or commas (','), with the leading dot. When
18 set, the resolv+ library will automatically trim the given
19 domain name from the end of any hostname resolved via DNS. This
20 is intended for use with local hosts and domains. (Related
21 note: trim will not affect hostnames gathered via NIS or the
22 hosts file. Care should be taken to ensure that the first host‐
23 name for each entry in the hosts file is fully qualified or
24 unqualified, as appropriate for the local installation.)
25 multi Valid values are on and off. If set to on, the resolv+ library
27 will return all valid addresses for a host that appears in the
28 /etc/hosts file, instead of only the first. This is off by
29 default, as it may cause a substantial performance loss at sites
30 with large hosts files.
31 nospoof
33 Valid values are on and off. If set to on, the resolv+ library
34 will attempt to prevent hostname spoofing to enhance the secu‐
35 rity of rlogin and rsh. It works as follows: after performing a
36 host address lookup, resolv+ will perform a hostname lookup for
37 that address. If the two hostnames do not match, the query will
38 fail. The default value is off.
39 spoofalert
41 Valid values are on and off. If this option is set to on and
42 the nospoof option is also set, resolv+ will log a warning of
43 the error via the syslog facility. The default value is off.
44 spoof Valid values are off, nowarn and warn. If this option is set to
46 off, spoofed addresses are permitted and no warnings will be
47 emitted via the syslog facility. If this option is set to warn,
48 resolv+ will attempt to prevent hostname spoofing to enhance the
49 security and log a warning of the error via the syslog facility.
50 If this option is set to nowarn, the resolv+ library will
51 attempt to prevent hostname spoofing to enhance the security but
52 not emit warnings via the syslog facility. Setting this option
53 to anything else is equal to setting it to nowarn.
54 reorder
56 Valid values are on and off. If set to on, resolv+ will attempt
57 to reorder host addresses so that local addresses (i.e., on the
58 same subnet) are listed first when a gethostbyname(3) is per‐
59 formed. Reordering is done for all lookup methods. The default
60 value is off.
61
63 There are six environment variables that can be used to allow users to
64 override the behavior which is configured in /etc/host.conf.
65 RESOLV_HOST_CONF
67 If set this variable points to a file that should be read
68 instead of /etc/host.conf.
69 RESOLV_SPOOF_CHECK
71 Overrides the nospoof, spoofalert and spoof commands in the same
72 way as the spoof command is parsed. Valid values are off,
73 nowarn and warn.
74 RESOLV_MULTI
76 Overrides the multi command.
77 RESOLV_REORDER
79 Overrides the reorder command.
80 RESOLV_ADD_TRIM_DOMAINS
82 A list of domains, separated by colons (':'), semicolons (';')
83 or commas (','), with the leading dot, which will be added to
84 the list of domains that should be trimmed.
85 RESOLV_OVERRIDE_TRIM_DOMAINS
87 A list of domains, separated by colons (':'), semicolons (';')
88 or commas (','), with the leading dot, which will replace the
89 list of domains that should be trimmed. Overrides the trim com‐
90 mand.
91
93 /etc/host.conf
94 Resolver configuration file
95 /etc/resolv.conf
97 Resolver configuration file
98 /etc/hosts
100 Local hosts database
101
103 The following differences exist compared to the original implementa‐
104 tion. A new command spoof and a new environment variable
105 RESOLV_SPOOF_CHECK can take arguments like off, nowarn and warn. Line
106 comments can appear anywhere and not only at the beginning of a line.
107
109 gethostbyname(3), hostname(7), named(8), resolv+[22m(8)
110
112 This page is part of release 3.53 of the Linux man-pages project. A
113 description of the project, and information about reporting bugs, can
114 be found at http://www.kernel.org/doc/man-pages/.
115Linux 2003-08-23 HOST.CONF(5)