NAME

nslookup − Queries Internet name servers interactively

SYNOPSIS

nslookup [−option ...] [host-to-find | [−server] ]

DESCRIPTION

The nslookup command is a program that is used to query Internet domain name servers.  The nslookup command has two modes: interactive and noninteractive. 

Noninteractive mode
Noninteractive mode is used to print just the name and requested information for a host or domain.  Noninteractive mode is invoked when the name or Internet address of the host to be looked up is given as the first argument. The optional second argument specifies the hostname or address of a name server.

Interactive mode
Interactive mode allows the user to query name servers for information about various hosts and domains or to print a list of hosts in a domain.  Interactive mode is invoked when you specify nslookup without arguments (the default name server will be used), or when the first argument you specify is a - (dash) and the second argument is the hostname or Internet address of a name server. 

The options listed under the set command can be specified in the .nslookuprc file in the user’s home directory if they are listed one per line. Options can also be specified on the command line if they precede the arguments and are prefixed with a - (dash).  For example, to change the default query type to host information, and the initial time-out to 10 seconds, enter:

nslookup −query=hinfo  −timeout=10

Interactive Commands

Commands may be interrupted at any time by entering <Ctrl-c>. To exit, enter <Ctrl-d> (EOF) or type exit. The command line length must be less than 256 characters.  To treat a built-in command as a hostname, precede it with an escape character \ (backslash). Note that an unrecognized command will be interpreted as a hostname. 

host [server]
Looks up information for host using the current default server or using server if specified.  If host is an Internet address and the query type is A or PTR, the name of the host is returned. If host is a name and 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 not in the current domain, append a . (dot) to the name. 

server domain

lserver domain
Changes 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 cannot be found, the names of servers that might have the answer are returned. 

root
Changes 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 lserver ns.internic.net.) The name of the root server can be changed with the set root command. 

finger [name] [> filename]

finger [name] [>> filename]
Connects with the finger server on the current host. The current host is defined when a previous lookup for a host was successful and returned address information (see the set querytype=A command).  name is optional. The> and >> (redirection symbols) can be used to redirect output in the usual manner. 

ls [option] domain [> filename]

ls [option] domain [>> filename]
Lists the information available for domain, optionally creating or appending to filename. The default output contains hostnames and their Internet addresses.  option can be one of the following:

−t querytype
Lists all records of the specified type (see querytype later in this reference page). 

−aLists aliases of hosts in the domain.  This option is a synonym for −t CNAME. 

−dLists all records for the domain.  This option is a synonym for -t ANY. 

−hLists CPU and operating system information for the domain. This option is a synonym for -t HINFO. 

−sLists well-known services of hosts in the domain. This option is a synonym for -t WKS.  When output is directed to a file, # (number signs) are printed for every 50 records received from the server. 

view filename
Sorts and lists the output of previous ls command(s) with more. 

help

?Prints a brief summary of commands. 

exitExits the program. 

set keyword[=value]
This command is used to change state information that affects the lookups. Valid keywords are:

allPrints the current values of the frequently used options to set. Information about the  current default server and host is also printed. 

class=value
Changes the query class to one of:

INThe Internet class. 

CHAOS
The Chaos class.

HESIOD
The MIT Athena Hesiod class.

ANY
Wildcard (any of the above). The class specifies the protocol group of the information. (Default = IN, abbreviation = cl)

[no]debug
Turns debugging mode on. A lot more information is printed about the packet sent to the server and the resulting answer. (Default = nodebug, abbreviation = [no]deb)

[no]d2Turns exhaustive debugging mode on. Essentially all fields of every packet are printed. (Default = nod2)

domain=name
Changes the default domain name to name.  The default domain name is appended to a lookup request depending on the state of the defname and search options. 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. (Default = value from hostname, /etc/resolv.conf or LOCALDOMAIN, abbreviation = do)

srchlist=name1/name2/...
Changes the default domain name to name1 and the domain search list to name1, name2, and so on. A maximum of 6 names separated by / (slashes) can be specified: For example:

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

sets the domain to lcs.MIT.EDU and the search list to the 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. (Default = value based on hostname, /etc/resolv.conf or LOCALDOMAIN, abbreviation = srchl)

[no]defname
If set, appends the default domain name to a single-component lookup request (that is, one that does not contain a dot). (Default = defname, abbreviation = [no]def)

[no]search
If the lookup request contains at least one . (dot) but does not end with a trailing dot, appends the domain names in the domain search list to the request until an answer is received. (Default = search, abbreviation = [no]sea)

port=value
Changes the default TCP/UDP name server port to value.  (Default = 53, abbreviation = po)

querytype=value

type=value
Changes the type of information query to one of:

AThe host’s IPv4 address. 

AAAA
The host’s IPv6 address.

CNAME
The canonical name for an alias.

HINFO
The host CPU and operating system type.

MINFO
The mailbox or mail list information.

MXThe mail exchanger. 

NAPTR
The Naming AUthority PoinTeR that contains rules for mapping parts of Uniform Resource Identifiers (URIs) to domain names.

NSThe name server for the named zone. 

PTR
The hostname if the query is an Internet address; otherwise the pointer to other information.

SOA
The domain’s start-of-authority information.

SRV
The host that can provide a specific resolution service.

TXT
The text information.

UINFO
The user information.

WKS
The supported well-known services. Other types (ANY, AXFR, MB, MD, MF, NULL) are described in the RFC1035 document. (Default = A, abbreviations = q, ty)

[no]recurse
Tells the name server to query other servers if it does not have the information.  (Default = recurse, abbreviation = [no]rec)

retry=number
Sets the number of retries to number. When a reply to a request is not received within a certain amount of time (changed with set time-out), the timeout period is doubled and the request is resent. The retry value controls how many times a request is resent before giving up. (Default = 4, abbreviation = ret)

root=host
Changes the name of the root server to host.  This affects the root command. (Default = ns.internic.net., abbreviation = ro)

timeout=number
Changes the initial timeout interval for waiting for a reply to number seconds. Each retry doubles the timeout period. (Default = 5 seconds, abbreviation = ti)

[no]vcAlways use a virtual circuit when sending requests to the server. (Default = novc, abbreviation = [no]v)

[no]ignoretc
Ignore packet truncation errors. (Default = noignoretc, abbreviation = [no]ig)

EXIT STATUS

In noninteractive mode, nslookup can return the following values:

0A match was found. 

1No match was found, or an error occurred. 

ERRORS

If the lookup request was not successful, an error message is printed.  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 hostname is valid. The query type is specified with the set querytype command. 

Nonexistent domain
The host or domain name does not exist.

Connection refused

Network is unreachable
The connection to the name or finger server could 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. It may indicate an error in nslookup. 

FILES

/usr/bin/nslookup
Specifies the command path

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

$HOME/.nslookuprc
User’s initial options

/usr/share/misc/nslookup.help
Summary of commands

SEE ALSO

Commands: named(8)

Functions: resolver(4)

Files: resolv.conf(4)

Specifications:  RFC1034, RFC1035