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53 .\" $Id: host.1,v 8.2 1997/03/14 02:29:44 vixie Exp $
61 .Nd look up host names using domain server
71 looks for information about Internet hosts. It gets this information
72 from a set of interconnected servers that are spread across the
73 country. By default, it simply converts between host names and
74 Internet addresses. However, with the
78 options, it can be used
79 to find all of the information about this host that is maintained
82 The arguments can be either host names or host numbers. The program
83 first attempts to interpret them as host numbers. If this fails,
84 it will treat them as host names. A host number consists of
85 four decimal numbers separated by dots, e.g. 128.6.4.194
86 A host name consists of names separated by dots, e.g. topaz.rutgers.edu.
87 Unless the name ends in a dot, the local domain
88 is automatically tacked on the end. Thus, a Rutgers user can say
92 and it will actually look up "topaz.rutgers.edu".
93 If this fails, the name is tried unchanged (in this case, "topaz").
94 This same convention is used for mail and other network utilities.
95 The actual suffix to tack on the end is obtained
96 by looking at the results of a
97 .Xr hostname @CMD_EXT@
98 call, and using everything
99 starting at the first dot. (See below for a description of
100 .Sx CUSTOMIZING HOST NAME LOOKUP . )
102 The first argument is the host name you want to look up.
103 If this is a number, an
105 is done, i.e. the domain
106 system looks in a separate set of databases used to convert numbers
109 The second argument is optional. It
110 allows you to specify a particular server to query. If you don't
111 specify this argument, the default server (normally the local machine)
114 If a name is specified, you may see output of three different kinds.
115 Here is an example that shows all of them:
118 .Dl sun4.rutgers.edu is a nickname for ATHOS.RUTGERS.EDU
119 .Dl ATHOS.RUTGERS.EDU has address 128.6.5.46
120 .Dl ATHOS.RUTGERS.EDU has address 128.6.4.4
121 .Dl ATHOS.RUTGERS.EDU mail is handled by ARAMIS.RUTGERS.EDU
123 The user has typed the command
125 The first line indicates that the name
126 .Dq Li sun4.rutgers.edu
127 is actually a nickname. The official host name is
128 .Dq Li ATHOS.RUTGERS.EDU .
129 The next two lines show the
130 address. If a system has more than one network interface, there
131 will be a separate address for each. The last line indicates
133 .Li ATHOS.RUTGERS.EDU
134 does not receive its own mail. Mail for
136 .Li ARAMIS.RUTGERS.EDU .
137 There may be more than one
138 such line, since some systems have more than one other system
139 that will handle mail for them. Technically, every system that
140 can receive mail is supposed to have an entry of this kind. If
141 the system receives its own mail, there should be an entry
142 the mentions the system itself; for example,
144 .D1 Li XXX mail is handled by XXX
146 However, many systems that receive
147 their own mail do not bother to mention that fact. If a system
149 .Dq Li mail is handled by
150 entry, but no address, this indicates
151 that it is not really part of the Internet, but a system that is
152 on the network will forward mail to it. Systems on Usenet, Bitnet,
153 and a number of other networks have entries of this kind.
155 There are a number of options that can be used before the
156 host name. Most of these options are meaningful only to the
157 staff who have to maintain the domain database.
161 this is equivalent to
162 .Dq Fl v Fl t Cm any .
166 to look for non-Internet data.
168 Turn on debugging. Network transactions are shown in detail.
170 List a complete domain; e.g.:
172 .D1 Ic host -l rutgers.edu
174 will give a listing of all hosts in the rutgers.edu domain. The
176 option is used to filter what information is presented, as you
177 would expect. The default is address information, which also
178 include PTR and NS records. The command
180 .D1 Ic host -l -v -t any rutgers.edu
182 will give a complete download of the zone data for rutgers.edu,
183 in the official master file format. (However the SOA record is
184 listed twice, for arcane reasons.)
189 doing a complete zone transfer and then filtering out the information
190 that you have asked for. This command should be used only if it
191 is absolutely necessary.
193 Turn off recursion in the request.
194 This means that the name server will return only data it has in
195 its own database. It will not ask other servers for more
197 .It Fl t Ar querytype
198 Allows you to specify a particular
201 to be looked up. The arguments are defined in the man page for
202 .Xr @INDOT@named @SYS_OPS_EXT@ .
203 Currently-supported types include:
223 Additionally, the wildcard, which may be written
228 can be used to specify any (all) of the above types.
229 Types must be given in lower case.
230 Note that the default is to look first for
234 except that if the verbose option is turned on, the default is only
238 option is particularly useful for filtering information returned by
240 see the explanation of the
242 option for more information.
244 Use "verbose" format for printout. This
245 is the official domain master file format, which is documented
247 .Xr @INDOT@named @SYS_OPS_EXT@ .
248 Without this option, output still follows
249 this format in general terms, but some attempt is made to make it
250 more intelligible to normal users. Without
252 any "a", "mx", and "cname" records
253 are written out as "has address", "mail is handled by", and
254 "is a nickname for" (respectively), and TTL and class fields are not shown.
258 to wait forever for a response. Normally
259 it will time out after approximate one minute.
260 .Sh CUSTOMIZING HOST NAME LOOKUP
261 In general, if the name supplied by the user does not
262 have any dots in it, a default domain is appended to the end.
263 This domain can be defined in
264 .Pa /etc/resolv.conf ,
265 but is normally derived
266 by taking the local hostname after its first dot. The user can override
267 this, and specify a different default domain, using the environment
270 In addition, the user can supply his own abbreviations for host names.
271 They should be in a file consisting of one line per abbreviation.
272 Each line contains an abbreviation, a space, and then the full
273 host name. The name file must be contained in the
275 environment variable.
277 .Bl -tag -width "/etc/resolv.conf " -compress
279 Name of file containing
280 .Pq Ar host alias , full hostname
284 .Bl -tag -width "/etc/resolv.conf " -compress
285 .It Pa /etc/resolv.conf
287 .Xr resolver @FORMAT_EXT@ .
289 Name of file containing
290 .Pq Ar host alias , full hostname
294 .Xr @INDOT@named @SYS_OPS_EXT@ ,
295 .Xr resolver @FORMAT_EXT@ .
297 Unexpected effects can happen when you type a name that is not
298 part of the local domain. Please always keep in mind the
299 fact that the local domain name is tacked onto the end of every
300 name, unless it ends in a dot. Only if this fails is the name
305 option only tries the first name server listed for the
306 domain that you have requested. If this server is dead, you
307 may need to specify a server manually. E.g., to get a listing
308 of foo.edu, you could try
310 .D1 Ic host -t ns foo.edu
312 to get a list of all the name servers for foo.edu, and then try
314 .D1 Ic host -l foo.edu xxx
318 on the list of name servers, until you find one that works.