1HOST.CONF(5) Linux System Administration HOST.CONF(5)
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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 following
12 keywords are recognized:
13 trim This keyword may be listed more than once. Each time it should
15 be followed by a list of domains, separated by colons (':'),
16 semicolons (';') or commas (','), with the leading dot. When
17 set, the resolver library will automatically trim the given
18 domain name from the end of any hostname resolved via DNS. This
19 is intended for use with local hosts and domains. (Related
20 note: trim will not affect hostnames gathered via NIS or the
21 hosts(5) file. Care should be taken to ensure that the first
22 hostname for each entry in the hosts file is fully qualified or
23 unqualified, as appropriate for the local installation.)
24 multi Valid values are on and off. If set to on, the resolver library
26 will return all valid addresses for a host that appears in the
27 /etc/hosts file, instead of only the first. This is off by
28 default, as it may cause a substantial performance loss at sites
29 with large hosts files.
30 reorder
32 Valid values are on and off. If set to on, the resolver library
33 will attempt to reorder host addresses so that local addresses
34 (i.e., on the same subnet) are listed first when a gethostby‐
35 name(3) is performed. Reordering is done for all lookup meth‐
36 ods. The default value is off.
37
39 The following environment variables can be used to allow users to over‐
40 ride the behavior which is configured in /etc/host.conf:
41 RESOLV_HOST_CONF
43 If set, this variable points to a file that should be read
44 instead of /etc/host.conf.
45 RESOLV_MULTI
47 Overrides the multi command.
48 RESOLV_REORDER
50 Overrides the reorder command.
51 RESOLV_ADD_TRIM_DOMAINS
53 A list of domains, separated by colons (':'), semicolons (';')
54 or commas (','), with the leading dot, which will be added to
55 the list of domains that should be trimmed.
56 RESOLV_OVERRIDE_TRIM_DOMAINS
58 A list of domains, separated by colons (':'), semicolons (';')
59 or commas (','), with the leading dot, which will replace the
60 list of domains that should be trimmed. Overrides the trim com‐
61 mand.
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64 /etc/host.conf
65 Resolver configuration file
66 /etc/resolv.conf
68 Resolver configuration file
69 /etc/hosts
71 Local hosts database
72
74 The following differences exist compared to the original implementa‐
75 tion. A new command spoof and a new environment variable
76 RESOLV_SPOOF_CHECK can take arguments like off, nowarn, and warn. Line
77 comments can appear anywhere and not only at the beginning of a line.
78 Historical
80 The nsswitch.conf(5) file is the modern way of controlling the order of
81 host lookups.
82 In glibc 2.4 and earlier, the following keyword is recognized:
84 order This keyword specifies how host lookups are to be performed. It
86 should be followed by one or more lookup methods, separated by
87 commas. Valid methods are bind, hosts, and nis.
88 RESOLV_SERV_ORDER
90 Overrides the order command.
91 Since glibc 2.0.7, the following keywords and environment variable have
93 been recognized but never implemented:
94 nospoof
96 Valid values are on and off. If set to on, the resolver library
97 will attempt to prevent hostname spoofing to enhance the secu‐
98 rity of rlogin and rsh. It works as follows: after performing a
99 host address lookup, the resolver library will perform a host‐
100 name lookup for that address. If the two hostnames do not
101 match, the query fails. The default value is off.
102 spoofalert
104 Valid values are on and off. If this option is set to on and
105 the nospoof option is also set, the resolver library will log a
106 warning of the error via the syslog facility. The default value
107 is off.
108 spoof Valid values are off, nowarn, and warn. If this option is set
110 to off, spoofed addresses are permitted and no warnings will be
111 emitted via the syslog facility. If this option is set to warn,
112 the resolver library will attempt to prevent hostname spoofing
113 to enhance the security and log a warning of the error via the
114 syslog facility. If this option is set to nowarn, the resolver
115 library will attempt to prevent hostname spoofing to enhance the
116 security but not emit warnings via the syslog facility. Setting
117 this option to anything else is equal to setting it to nowarn.
118 RESOLV_SPOOF_CHECK
120 Overrides the nospoof, spoofalert, and spoof commands in the
121 same way as the spoof command is parsed. Valid values are off,
122 nowarn, and warn.
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125 gethostbyname(3), hosts(5), nsswitch.conf(5), resolv.conf(5), host‐
126 name(7), named(8)
127
129 This page is part of release 4.16 of the Linux man-pages project. A
130 description of the project, information about reporting bugs, and the
131 latest version of this page, can be found at
132 https://www.kernel.org/doc/man-pages/.
133Linux 2017-09-15 HOST.CONF(5)