1HOST.CONF(5) Linux System Administration HOST.CONF(5)
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6 host.conf - resolver configuration file
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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 on by
28 default. On systems with DNS, hosts files are much smaller and
29 the performance loss of multiple search is negligible. On sites
30 with large hosts files, turning it on may cause a substantial
31 performance loss.
32 reorder
34 Valid values are on and off. If set to on, the resolver library
35 will attempt to reorder host addresses so that local addresses
36 (i.e., on the same subnet) are listed first when a gethostby‐
37 name(3) is performed. Reordering is done for all lookup meth‐
38 ods. The default value is off.
39
41 The following environment variables can be used to allow users to over‐
42 ride the behavior which is configured in /etc/host.conf:
43 RESOLV_HOST_CONF
45 If set, this variable points to a file that should be read
46 instead of /etc/host.conf.
47 RESOLV_MULTI
49 Overrides the multi command.
50 RESOLV_REORDER
52 Overrides the reorder command.
53 RESOLV_ADD_TRIM_DOMAINS
55 A list of domains, separated by colons (':'), semicolons (';')
56 or commas (','), with the leading dot, which will be added to
57 the list of domains that should be trimmed.
58 RESOLV_OVERRIDE_TRIM_DOMAINS
60 A list of domains, separated by colons (':'), semicolons (';')
61 or commas (','), with the leading dot, which will replace the
62 list of domains that should be trimmed. Overrides the trim com‐
63 mand.
64
66 /etc/host.conf
67 Resolver configuration file
68 /etc/resolv.conf
70 Resolver configuration file
71 /etc/hosts
73 Local hosts database
74
76 The following differences exist compared to the original implementa‐
77 tion. A new command spoof and a new environment variable
78 RESOLV_SPOOF_CHECK can take arguments like off, nowarn, and warn. Line
79 comments can appear anywhere and not only at the beginning of a line.
80 Historical
82 The nsswitch.conf(5) file is the modern way of controlling the order of
83 host lookups.
84 In glibc 2.4 and earlier, the following keyword is recognized:
86 order This keyword specifies how host lookups are to be performed. It
88 should be followed by one or more lookup methods, separated by
89 commas. Valid methods are bind, hosts, and nis.
90 RESOLV_SERV_ORDER
92 Overrides the order command.
93 Since glibc 2.0.7, and up through glibc 2.24, the following keywords
95 and environment variable have been recognized but never implemented:
96 nospoof
98 Valid values are on and off. If set to on, the resolver library
99 will attempt to prevent hostname spoofing to enhance the secu‐
100 rity of rlogin and rsh. It works as follows: after performing a
101 host address lookup, the resolver library will perform a host‐
102 name lookup for that address. If the two hostnames do not
103 match, the query fails. The default value is off.
104 spoofalert
106 Valid values are on and off. If this option is set to on and
107 the nospoof option is also set, the resolver library will log a
108 warning of the error via the syslog facility. The default value
109 is off.
110 spoof Valid values are off, nowarn, and warn. If this option is set
112 to off, spoofed addresses are permitted and no warnings will be
113 emitted via the syslog facility. If this option is set to warn,
114 the resolver library will attempt to prevent hostname spoofing
115 to enhance the security and log a warning of the error via the
116 syslog facility. If this option is set to nowarn, the resolver
117 library will attempt to prevent hostname spoofing to enhance the
118 security but not emit warnings via the syslog facility. Setting
119 this option to anything else is equal to setting it to nowarn.
120 RESOLV_SPOOF_CHECK
122 Overrides the nospoof, spoofalert, and spoof commands in the
123 same way as the spoof command is parsed. Valid values are off,
124 nowarn, and warn.
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127 gethostbyname(3), hosts(5), nsswitch.conf(5), resolv.conf(5), host‐
128 name(7), named(8)
129
131 This page is part of release 4.15 of the Linux man-pages project. A
132 description of the project, information about reporting bugs, and the
133 latest version of this page, can be found at
134 https://www.kernel.org/doc/man-pages/.
135Linux 2017-09-15 HOST.CONF(5)