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