nslookup - Queries Internet name servers interactively
Noninteractive Mode
nslookup [-option ...] host-to-find [server]
Interactive Mode [Toc] [Back]
nslookup [-option ...] [- server]
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 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 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 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 [Toc] [Back]
Commands may be interrupted at any time by entering <Ctrlc>.
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.
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. 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. 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. 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. 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:
Lists all records of the specified type (see
querytype later in this reference page). Lists aliases of
hosts in the domain. This option is a synonym for -t
CNAME. Lists all records for the domain. This option is
a synonym for -t ANY. Lists CPU and operating system
information for the domain. This option is a synonym for
-t HINFO. Lists 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. Sorts and
lists the output of previous ls command(s) with more.
Prints a brief summary of commands. Exits the program.
This command is used to change state information that
affects the lookups. Valid keywords are: Prints the current
values of the frequently used options to set. Information
about the current default server and host is also
printed. Changes the query class to one of: The Internet
class. The Chaos class. The MIT Athena Hesiod class.
Wildcard (any of the above). The class specifies the protocol
group of the information. (Default = IN, abbreviation
= cl) 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) Turns exhaustive debugging mode on. Essentially
all fields of every packet are printed. (Default = nod2)
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)
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) 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) 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) Changes
the default TCP/UDP name server port to value.
(Default = 53, abbreviation = po) Changes the type
of information query to one of: The host's IPv4
address. The host's IPv6 address. The canonical
name for an alias. The host CPU and operating system
type. The mailbox or mail list information.
The mail exchanger. The Naming AUthority PoinTeR
that contains rules for mapping parts of Uniform
Resource Identifiers (URIs) to domain names. The
name server for the named zone. The hostname if
the query is an Internet address; otherwise the
pointer to other information. The domain's startof-authority
information. The host that can provide
a specific resolution service. The text
information. The user information. The supported
well-known services. Other types (ANY, AXFR, MB,
MD, MF, NULL) are described in the RFC1035 document.
(Default = A, abbreviations = q, ty) Tells
the name server to query other servers if it does
not have the information. (Default = recurse,
abbreviation = [no]rec) 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) Changes the
name of the root server to host. This affects the
root command. (Default = ns.internic.net., abbreviation
= ro) Changes the initial timeout interval
for waiting for a reply to number seconds. Each
retry doubles the timeout period. (Default = 5 seconds,
abbreviation = ti) Always use a virtual circuit
when sending requests to the server. (Default
= novc, abbreviation = [no]v) Ignore packet truncation
errors. (Default = noignoretc, abbreviation =
[no]ig)
In noninteractive mode, nslookup can return the following
values: A match was found. No match was found, or an
error occurred.
If the lookup request was not successful, an error message
is printed. Possible errors are: 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 name server is
running on the server machine. 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. The host or domain
name does not exist. 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. The name
server found an internal inconsistency in its database and
could not return a valid answer. The name server refused
to service the request. The name server found that the
request packet was not in the proper format. It may indicate
an error in nslookup.
Specifies the command path Initial domain name and name
server addresses User's initial options Summary of commands
Commands: named(8)
Functions: resolver(4)
Files: resolv.conf(4)
Specifications: RFC1034, RFC1035
nslookup(8)
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