NAME

nslookup − query name servers interactively

SYNOPSIS

nslookup [ − option ]... host [ server ]

nslookup [ − option ]... − [ server ]

nslookup

DESCRIPTION

nslookup sends queries to Internet domain name servers.  It has two modes: interactive and non-interactive.  Interactive mode allows the user to contact servers for information about various hosts and domains or to display a list of hosts in a domain.  Non-interactive mode is used to display just the name and requested information for a host or domain. 

OPTIONS

−option Set the permissible options, as shown in the following list.  These are the same options that the set command supports in interactive mode (see set in the Commands section for more complete descriptions). 

all List the current settings

class=classname Restrict search according to the specified class

d2 Set exhaustive debug mode on

nod2 Set exhaustive debug mode off

debug Set debug mode on

nodebug Set debug mode off

defname Set domain-appending mode on

nodefname Set domain-appending mode off

domain=string Establish the appendable domain

ignoretc Set it to ignore packet truncation errors

noignoretc Set it to acknowledge packet truncation errors

OPERANDS

host Inquires about the specified host. In this non-interactive command format, nslookup Does not prompt for additional commands. 

− Causes nslookup to prompt for more information, such as host names, before sending one or more queries. 

server Directs inquiries to the name server specified here in the command line rather than the one read from the /etc/resolv.conf file (see resolv.conf(4)).  server can be either a name or an Internet address.  If the specified host cannot be reached, nslookup resorts to using the name server specified in /etc/resolv.conf. 

USAGE

Non-interactive Mode

Non-interactive mode is selected when the name or Internet address of the host to be looked up is given as the first argument. 

Within non-interactive mode, space-separated options can be specified. They must be entered before the host name, to be queried.  Each option must be prefixed with a hyphen. 

For example, to request extensive host information and to set the timeout to 10 seconds when inquiring about gypsy, enter:

example% nslookup −query=hinfo −timeout=10 gypsy

To avoid repeated entry of an option that you almost always use, place a corresponding set command in a .nslookuprc file located inside your home directory. (See Commands for more information about set.)  The .nslookuprc file can contain several set commands if each is followed by a RETURN. 

Entering and Leaving Interactive Mode

Interactive mode is selected when

• No arguments are supplied. 

• A `−´ (hyphen) character is supplied as the host argument. 

To exit from an interactive nslookup session, type Control-d or type the command exit followed by RETURN . 

Supported Command Interactions

The commands associated with interactive mode are subject to various limitations and run-time conventions. 

The maximum length of a command line is 255 characters.  When the RETURN key is pressed, command-line execution begins.  While a command is running, its execution can be interrupted by typing Control-c. 

The first word entered on the command line must be the name of a nslookup command unless you wish to enter the name of a host to inquire about.  Any unrecognized command is handled as a host name to inquire about.  To force a command to be treated as a host name to be inquired about, precede it with a backslash character. 

Commands

exit Exit the nslookup program. 

help

? Display a brief summary of commands. 

host [ server ] Look up information for host using the current default server, or using server if it is specified. 

If the host supplied is an Internet address and the query type is A or PTR, the name of the host is returned.  If the host supplied is a name and it does not have a trailing period, the default domain name is appended to the name.  (This behavior depends on the state of the set options domain, srchlist, defname, and search). 

To look up a host that is not in the current domain, append a period to the name. 

finger [ name ] [ >> filename ]
Connect with the finger server on the current host, which is defined by the most recent successful host lookup.

If no name value is specified, a list of login account names on the current host is generated. 

Similar to a shell command interpreter, output can be redirected to a file using the usual redirection symbols: > and >>. 

ls [ −options ] domain [  >> filename ]
List the information available for domain, optionally creating or appending to filename. The default output contains host names and their Internet addresses.

Output can be redirected to filename using the > and >> redirection symbols.  When output is directed to a file, hash marks are shown for every 50 records received from the server.  The permissible values for options are:

a Lists aliases of hosts in the domain.  This is a synonym for the command ls −t CNAME. 

d Lists all records for the domain.  This is a synonym for the command ls −t ANY. 

h Lists CPU and operating system information for the domain.  This is a synonym for the command ls −t HINFO. 

s Lists well-known services of hosts in the domain.  This is a synonym for the command ls −t WKS. 

t querytype-value
lists all records of the specified type (see querytype within the discussion of the set command). 

set token=value

set keyword Establish a preferred mode of search operation.  Permissible token and keyword values are:

all Display the current values of frequently-used options.  Information about the current default server and host is also displayed. 

cl[ass]=classname
Limit the search according to the protocol group (classname) for which lookup information is desired.
Permissible classname values are:

ANY A wildcard selecting all classes

IN The Internet class (the default)

CHAOS The Chaos class. 

HESIOD The MIT Athena Hesiod class. 

d2

nod2 Enable or disable exhaustive debugging mode.  Essentially all fields of every packet are displayed.  By default, this option is disabled. 

deb[ug]

nodeb[ug]
Enable or disable debugging mode. When debugging mode is enabled, much more information is produced about the packet sent to the server and the resulting answer. By default, this option is disabled.

def[name]

nodef[name]
Enable or disable appending the default domain name to a single-component lookup request (one that lacks a dot). By default, this option is enabled for nslookup.  The default value for the domain name is the value given in /etc/resolv.conf, unless: there is an environmental value for LOCALDOMAIN when nslookup is run; a recent value has been specified through the srchlist command or the set domain command. 

do[main]=string
Change the default domain name to be appended to all lookup requests to string.  For this option to have any effect, the defname option must also be enabled and the search option must be set in a compatible way. 

The domain search list contains the parents of the default domain if it has at least two components in its name.  For example, if the default domain is CC.Berkeley.EDU, the search list is CC.Berkeley.EDU and Berkeley.EDU. Use the set srchlist command to specify a different list.  Use the set all command to display the list. 

ignoretc

noignoretc
Ignore packet truncation errors. By default, this option is disabled.

srch[list]=name1/name2/...
Change the default domain name to name1 and the domain search list to name1, name2, etc.  A maximum of 6 names can be specified, along with slash characters to separate them.  For example,

example% set srchlist=lcs.MIT.EDU/ai.MIT.EDU/MIT.EDU

sets the domain to lcs.MIT.EDU and the search list to all three names.  This command overrides the default domain name and search list of the set domain command.  Use the set all command to display the list. 

search

nosearch
Enable or disable having the domain names in the domain search list appended to the request, generating a series of lookup queries if necessary until an answer is received. To take effect, the lookup request must contain at least one dot (period); yet it must not contain a trailing period. By default, this option is enabled.

po[rt]=value
Specify the default TCP/UDP name server port.  By default, this value is 53. 

q[uerytype]=value

ty[pe]=value
Change the type of information returned from a query to one of:

A The Internet address of the host

CNAME The canonical name for an alias

HINFO The host CPU and operating system type

MD The mail destination

MX The mail exchanger

MB The mailbox domain name

MG The mail group member

MINFO The mailbox or mail list information

NS The name server

PTR The host name if the query is in the form of an Internet address; otherwise the pointer to other information

SOA The domain’s start-of-authority information

TXT The text information

UINFO The user information

WKS The supported well-known services

(Other types specified in the RFC 1035 document are valid, but they are not as useful.) 

recurse

norecurse
Enable or disable having to query other name servers before abandoning a search. By default, this feature is enabled.

ret[ry]=count
Set the maximum number of times to retry a request before abandoning a search. When a reply to a request is not received within a certain amount of time (changed with set timeout), the timeout period is doubled and the request is resent.  The retry value controls how many times a request is resent before the request is aborted.  The default for count is 4. 

ro[ot]=host
Change the name of the root server to host. This affects the root command.  The default root server is ns.internet.net. 

t[timeout]=interval
Change the amount of time to wait for a reply to interval seconds.  Each retry doubles the timeout period.  The default interval is 5 seconds. 

vc

novc
Enable or disable the use of a virtual circuit when sending requests to the server. By default, this feature is disabled.

root
Change the default server to the server for the root of the domain name space. Currently, the host ns.internic.net is used; this command is a synonym for server ns.internic.net.  The name of the root server can be changed with the set root command. 

server domain

lserver domain
Change the default server to domain. lserver uses the initial server to look up information about domain while server uses the current default server.  If an authoritative answer can not be found, the names of servers that might have the answer are returned. 

view filename
Sort the output of previous ls command(s) and display it one text screenful at a time, similar to more(1). 

EXAMPLES

To effectively search the Internet domain namespace, it helps to know its structure. At present, the Internet domain name-space is tree-structured, with one top level domain for each country except the U.S.A. There are also some traditional top level domains, not explicitly tied to any particular country.  These include:

COM Commercial establishments

EDU Educational institutions

ORG Not-for-profit organizations

GOV Government agencies

MIL MILNET hosts

If you are looking for a specific host, you need to know something about the host’s organization in order to determine the top-level domain that it belongs to.  For instance, if you want to find the Internet address of a machine at UCLA , do the following:

• Connect with the root server using the root command.  The root server of the name space has knowledge of the top-level domains. 

• Since UCLA is a university, its domain name is ucla.edu.  Connect with a server for the ucla.edu domain with the command server ucla.edu.  The response produces the names of hosts that act as servers for that domain.  Note: the root server does not have information about ucla.edu, but knows the names and addresses of hosts that do.  Once located by the root server, all future queries will be sent to the UCLA name server. 

• To request information about a particular host in the domain (for instance, locus), just type the host name.  To request a listing of hosts in the UCLA domain, use the ls command.  The ls command requires a domain name (in this case, ucla.edu) as an argument. 

If you are connected with a name server that handles more than one domain, all lookups for host names must be fully specified with its domain.  For instance, the domain harvard.edu is served by seismo.css.gov, which also services the css.gov and cornell.edu domains. A lookup request for the host aiken in the harvard.edu domain must be specified as aiken.harvard.edu.  However, the

set domain=name

and

set defname

commands can be used to automatically append a domain name to each request. 

After a successful lookup of a host, use the finger(1) command to see who is on the system, or to finger a specific person.  (finger requires the type to be A.) 

To get other information about the host, use the

set querytype=value

command to change the type of information desired and request another lookup. 

ENVIRONMENT

HOSTALIASES References the file containing host aliases

LOCALDOMAIN Overrides default domain

EXIT STATUS

The process returns the following values:

0On success. 

1On failure. 

FILES

/etc/resolv.conf initial domain name and name server addresses

$HOME/.nslookuprc initial option commands

/usr/lib/nslookup.help
summary of commands

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Availability	SUNWcsu

SEE ALSO

finger(1), more(1), in.named(1M), nstest(1M), resolver(3N), resolv.conf(4), attributes(5)

Mockapetris, Paul, Domain Names - Concepts and Facilities, RFC 1034, Network Information Center, SRI International, Menlo Park, Calif., November 1987. 

Mockapetris, Paul, Domain Names - Implementation and Specification, RFC 1035, Network Information Center, SRI International, Menlo Park, Calif., November 1987. 

DIAGNOSTICS

If the lookup request is successful, an error message is produced.  Possible errors are:

Timed out The server did not respond to a request after a certain amount of time (changed with set timeout=value) and a certain number of retries (changed with set retry=value). 

No response from server
No name server is running on the server machine.

No records The server does not have resource records of the current query type for the host, although the host name is valid.  The query type is specified with the set querytype command. 

Non-existent domain
The host or domain name does not exist.

Connection refused

Network is unreachable
The connection to the name or finger server can not be made at the current time. This error commonly occurs with ls and finger requests. 

Server failure The name server found an internal inconsistency in its database and could not return a valid answer. 

Refused The name server refused to service the request. 

Format error The name server found that the request packet was not in the proper format.  This may indicate an error in nslookup. 

SunOS 5.6  —  Last change: 7 Jan 1997