man5/host.conf.5

   1 .\" Copyright (c) 1997 Martin Schulze (joey@infodrom.north.de)
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  24 .\" Much of the text is copied from the manpage of resolv+(8).
  25 .\"
  26 .\" 2003-08-23 Martin Schulze <joey@infodrom.org> Updated according to glibc 2.3.2
  27 .TH HOST.CONF 5 2003-08-23 "Linux" "Linux System Administration"
  28 .SH NAME
  29 host.conf \- resolver configuration file
  30 .SH DESCRIPTION
  31 The file
  32 .I /etc/host.conf
  33 contains configuration information specific to the resolver library.
  34 It should contain one configuration keyword per line, followed by
  35 appropriate configuration information.
  36 The keywords recognized are
  37 .IR order ", " trim ", " multi ", " nospoof ", " spoof ", and " reorder .
  38 These keywords are described below.
  39 .TP
  40 .I order
  41 This keyword specifies how host lookups are to be performed.
  42 It should be followed by one or more lookup methods, separated by commas.
  43 Valid methods are
  44 .IR bind ", " hosts ", and " nis .
  45 .TP
  46 .I trim
  47 This keyword may be listed more than once.
  48 Each time it should be
  49 followed by a list of domains, separated by colons (\(aq:\(aq), semicolons
  50 (\(aq;\(aq) or commas (\(aq,\(aq), with the leading dot.
  51 When set, the
  52 resolv+ library will automatically trim the given domain name from the
  53 end of any hostname resolved via DNS.
  54 This is intended for use with
  55 local hosts and domains.
  56 (Related note: trim will not affect hostnames
  57 gathered via NIS or the hosts file.
  58 Care should be taken to
  59 ensure that the first hostname for each entry in the hosts file is
  60 fully qualified or unqualified, as appropriate for the local
  61 installation.)
  62 .TP
  63 .I multi
  64 Valid values are
  65 .IR on " and " off .
  66 If set to
  67 .IR on ,
  68 the resolv+ library will return all valid addresses for a host that
  69 appears in the
  70 .I /etc/hosts
  71 file,
  72 instead of only the first.
  73 This is
  74 .I off
  75 by default, as it may cause a substantial performance loss at sites
  76 with large hosts files.
  77 .TP
  78 .I nospoof
  79 Valid values are
  80 .IR on " and " off .
  81 If set to
  82 .IR on ,
  83 the resolv+ library will attempt to prevent hostname spoofing to
  84 enhance the security of
  85 .BR rlogin " and " rsh .
  86 It works as follows: after performing a host address lookup, resolv+
  87 will perform a hostname lookup for that address.
  88 If the two hostnames
  89 do not match, the query will fail.
  90 The default value is
  91 .IR off .
  92 .TP
  93 .I spoofalert
  94 Valid values are
  95 .IR on " and " off .
  96 If this option is set to
  97 .I on
  98 and the
  99 .I nospoof
 100 option is also set, resolv+ will log a warning of the error via the
 101 syslog facility.
 102 The default value is
 103 .IR off .
 104 .TP
 105 .I spoof
 106 Valid values are
 107 .IR off ", " nowarn " and " warn .
 108 If this option is set to
 109 .IR off ,
 110 spoofed addresses are permitted and no warnings will be emitted
 111 via the syslog facility.
 112 If this option is set to
 113 .IR warn ,
 114 resolv+ will attempt to prevent hostname spoofing to
 115 enhance the security and log a warning of the error via the syslog
 116 facility.
 117 If this option is set to
 118 .IR nowarn ,
 119 the resolv+ library will attempt to prevent hostname spoofing to
 120 enhance the security but not emit warnings via the syslog facility.
 121 Setting this option to anything else is equal to setting it to
 122 .IR nowarn .
 123 .TP
 124 .I reorder
 125 Valid values are
 126 .IR on " and " off .
 127 If set to
 128 .IR on ,
 129 resolv+ will attempt to reorder host addresses so that local addresses
 130 (i.e., on the same subnet) are listed first when a
 131 .BR gethostbyname (3)
 132 is performed.
 133 Reordering is done for all lookup methods.
 134 The default value is
 135 .IR off .
 136 .SH ENVIRONMENT
 137 There are six environment variables that can be used to allow users to
 138 override the behavior which is configured in
 139 .IR /etc/host.conf .
 140 .TP
 141 .B RESOLV_HOST_CONF
 142 If set this variable points to a file that should be read instead of
 143 .IR /etc/host.conf .
 144 .TP
 145 .B RESOLV_SERV_ORDER
 146 Overrides the
 147 .I order
 148 command.
 149 .TP
 150 .B RESOLV_SPOOF_CHECK
 151 Overrides the
 152 .IR nospoof ", " spoofalert " and " spoof
 153 commands in the same way as the
 154 .I spoof
 155 command is parsed.
 156 Valid values are
 157 .IR off ", " nowarn " and " warn .
 158 .TP
 159 .B RESOLV_MULTI
 160 Overrides the
 161 .I multi
 162 command.
 163 .TP
 164 .B RESOLV_REORDER
 165 Overrides the
 166 .I reorder
 167 command.
 168 .TP
 169 .B RESOLV_ADD_TRIM_DOMAINS
 170 A list of domains,  separated by colons (\(aq:\(aq), semicolons (\(aq;\(aq) or
 171 commas (\(aq,\(aq), with the leading dot, which will be added to the list of
 172 domains that should be trimmed.
 173 .TP
 174 .B RESOLV_OVERRIDE_TRIM_DOMAINS
 175 A list of domains,  separated by colons (\(aq:\(aq), semicolons (\(aq;\(aq) or
 176 commas (\(aq,\(aq), with the leading dot, which will replace the list of
 177 domains that should be trimmed.
 178 Overrides the
 179 .I trim
 180 command.
 181 .SH FILES
 182 .TP
 183 .I /etc/host.conf
 184 Resolver configuration file
 185 .TP
 186 .I /etc/resolv.conf
 187 Resolver configuration file
 188 .TP
 189 .I /etc/hosts
 190 Local hosts database
 191 .SH NOTES
 192 The following differences exist compared to the original implementation.
 193 A new command
 194 .I spoof
 195 and a new environment variable
 196 .B RESOLV_SPOOF_CHECK
 197 can take arguments like
 198 .IR off ", " nowarn " and " warn .
 199 Line comments can appear anywhere and not only at the beginning of a line.
 200 .SH SEE ALSO
 201 .BR gethostbyname (3),
 202 .BR hostname (7),
 203 .BR named (8),
 204 .BR resolv+ (8)