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.

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.

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.

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 1PTR, 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.

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 United States.. 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.