nslookup(1)nslookup(1)NAMEnslookup - query name servers interactively
SYNOPSIS
Single Host Mode
host [server]
Interactive Mode
[server]]
DESCRIPTION
The program queries Internet domain name servers. It follows the con‐
figured name resolution algorithm of the host and queries NIS, DNS, and
host tables.
In (noninteractive), queries a name server for information about one
host or domain. This mode occurs when you specify a host in the com‐
mand.
In lets you make several requests in the same session. For example,
you can query a name server for information about various hosts and
domains or print a list of hosts in the domain. This mode occurs when
you omit the host (and server) in the command or when you use the spe‐
cial placeholder.
Options
Set the setoption, as defined for the command. See subsection in the
section.
Turn on tracing during command initialization,
causing the switch module to print out a trace of the scan
and parse actions on the database entry in the file (see nss‐
witch.conf(4)). It may be used to debug syntactic errors in
the switch configuration file. See also the option
Note: is a command option, so you cannot turn it off in
interactive mode.
Operands
host The host name or IP address of a host system. If host is
present, the command is executed immediately (noninterac‐
tively). If it is omitted, enters interactive mode.
Set interactive mode.
This placeholder is needed if you specify server for interac‐
tive mode.
server The host name or IP address of a domain name server. If
omitted, uses the policy described in the subsection.
Initialization File
The setoptions and (see the subsection) can be specified in a startup
file in the user's home directory. Enter them one per line without the
leading hyphen
Default Lookup Policy
If a server has not been specified explicitly to override the switch
policy, initializes each of the name services in the database in the
switch configuration file (see nsswitch.conf(4)), but uses the first
name service for lookup. The initialization of the name services may
cause a delay in obtaining the response if any of the name services is
not responding. For example, consider when the database is defined
with the following name services:
If the name servers mentioned in (see resolver(4)) are unavailable,
there will be a delay in trying to initialize the name servers. The
handling of the query thereafter follows the switch policy, as would be
expected.
contacts the name servers mentioned in sequentially but does not cycle
through them like the resolver routines do (see resolver(3N)).
Note: should not be used as a command-line substitute for the resolver
routines unless the differences in resolution behavior between and the
resolver routines are understood and are acceptable for the scripting
environment where will be employed.
The following name services are recognized:
Use the servers defined in the
file.
Use the entries in the
file.
Use the maps at the NIS server.
Note: NIS+ is not supported by If the name service is included in the
database, it is ignored.
If there is no database in the file or there is no file, uses this name
service sequence:
To override the switch policy and query DNS servers directly, you can
specify a name server by entering the server operand on the command
line or by using the or command in interactive mode. Whenever an
action is taken that causes the switch policy to be overridden, a warn‐
ing message is displayed.
If the first successful name service is or has a reduced interactive
command set; the command shows which commands are currently valid.
Use the command in interactive mode to restore the default policy.
INTERACTIVE COMMANDS
Commands can be interrupted at any time with the character, commonly
Ctrl-C. To exit, type the character, commonly Ctrl-D, or use the com‐
mand. (See stty(1).) To treat a built-in command as a host name, pre‐
cede it with an escape character When using NIS or the host table, only
host names and Internet addresses are allowed as commands. An unrecog‐
nized command is interpreted as a host name.
General Commands
host [server] Look 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 or the name of
the host is returned. If host is a name and does not
have a trailing period, one or more domains are appended
to the name. This behavior depends on the state of the
options and see Answers from a name server's cache are
labeled
See the command.
Exit the program.
Connects with the finger server on the current host.
name is a user name or user ID on the host; it is
optional. The current host is defined when a
previous lookup for a host was successful and
returned address information. The output can
create/overwrite or append to filename.
Print a brief summary of commands that are valid in the
current context.
List information available for
domain. The default output con‐
tains host names and their Internet
addresses. option can be one of
the following:
List aliases of hosts in the domain
(synonym for
List all records for the domain
(synonym for
List CPU and operating
system information
for the domain (syn‐
onym for
List well-known services of hosts
in the domain (synonym for
List all records of the specified
type.
See in
The output can create/overwrite or
append to filename. When output is
directed to a file, a character is
printed to standard output for
every 50 records received from the
server.
See the command.
Print out the policy read from the
database in the switch configura‐
tion file (see nsswitch.conf(4)).
The number of name services speci‐
fied in the file are shown, as well
as the order and criteria on how
the name services are to be used.
The four statuses of the criteria
are represented by four characters
in square brackets. The order of
the status characters is:
The letters used in the four status
positions are:
If no criteria are specified
between two sources, then the
default actions assigned to the
statuses are
Return to using the configured name service switch
policy
and reset to the original name
servers.
Change the default server to the server
for the root of the domain name
space. The command is a synonym
for where root-host is the root
server specified with the command.
The default root server is
Change the default server to
domain. uses the initial
server to look up informa‐
tion about domain while uses
the current default server.
When is used while the cur‐
rent name service being
pointed to is either NIS or
then the switch policy will
be overridden until a is
issued.
Change state information that affects
lookups.
See
Sort and list the contents of
filename, using (see
more(1)). This is useful
for viewing files written by
the and commands.
The set Command
The command changes state information that
affects the lookups. The options can also
be entered as setoption values on the com‐
mand line. For example,
The prefix
negates the request. The action is
described in brackets ([...]).
The keyword option is set to
value.
Other characters in brackets ([...]) are
optional, allowing for keyword abbrevia‐
tions. Spaces are not permitted.
Print the current values of the various
options, along with informa‐
tion about the current
default server and host.
Change the query class to one of:
The Internet class.
The Chaosnet class.
The MIT Athena Hesiod class.
Wildcard (any of the above).
The class specifies the pro‐
tocol group of the informa‐
tion. The default is
Turn on [turn off] exhaustive debugging
mode.
Essentially all fields of
every packet are printed.
The default is
Turn on [turn off] debugging mode.
More information is printed
about the packet sent to the
server and the resulting
answer. The default is
Append [do not append] the default domain
name
to a single-component lookup
request (that is, one that
does not contain a period
character). The default is
Change the default domain name to
name. The default domain
name is appended to a lookup
request, depending on the
state of the and options.
The domain search list con‐
tains the parents of the
default domain if it has at
least two components in its
name. For example, if the
default domain is the search
list is and Use the command
to specify a different list.
Use the command to display
the list. The default is
the value from host name, or
the environment variable.
Ignore [do not ignore] truncation errors.
The default is
Change the default TCP/UDP name server port
to
value. The default is
Change the type of information
returned from a query to one of:
Host's IPv4 address
Host's IPv6 address
All types of data
Canonical name for an
alias
Group ID
Host CPU and operat‐
ing system type
Mailbox domain name
Mail group member
Mailbox or mail list
information
Mail rename domain
name
Mail exchanger
Name server for the
named zone
Host name if the
query is an Internet
address,
otherwise
the pointer
to other
informa‐
tion.
Start of authority
record
Text information
User ID
User information
Well-known service
description
Tell the name server to query [not
to query] other servers
if it does not have
the information. The
default is
Set the number of retries to
number. When a reply
to a request is not
received within a
certain amount of
time (changed with
the command ), the
timeout period is
doubled and the
request is resent.
The retry value con‐
trols how many times
a request is resent
before giving up.
The default is
Change the name of the root server
to
host. This affects
the command. The
default is
If the lookup request contains at
least one period
but doesn't end with
a trailing period,
append [do not
append] the domain
names in the domain
search list to the
request until an
answer is received.
See hostname(5). The
default is
Change 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,
sets the domain to
and the search list
to the three names.
This command over‐
rides the default
domain name and
search list of the
command. Use the
command to display
the list. The
default is a value
based on the host
name, or the environ‐
ment variable.
Display [do not display] information
about the
sources used for
resolving a name or
an address lookup.
This flag traces the
behavior generated by
the switch policy.
The default is
Change the initial timeout interval
for waiting for a reply to
number seconds. Each
retry doubles the
timeout period. The
default is
See the option.
Always use [do not use] a virtual
circuit when sending requests to the
server.
The default is
DIAGNOSTICS
If the lookup request was not suc‐
cessful, an error message is
printed. Possible error messages
are:
The connection to the name server
could not be made
at the present time.
The name server found that the
request packet
was not in the proper for‐
mat.
The connection to the name server
could not be made
at the present time.
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 command.
No name server is running on the
server machine.
The host or domain name does not
exist.
The name server refused to service
the request.
The name server found an internal
inconsistency in its database
and could not return a
valid answer.
The server did not respond to a
request after a certain amount of
time (changed with value)
and a certain number of
retries (changed with
value).
EXAMPLES
To change the default query type to
host information and the initial
timeout to 10 seconds, and enter
interactive mode:
AUTHOR
was developed by the Internet Sys‐
tems Consortium (ISC).
FILES
User's initial options.
Host name data base.
Configuration file for the name-ser‐
vice switch.
Initial domain name and name server
addresses.
SEE ALSOmore(1), stty(1), named(1M),
resolver(3N), hosts(4), nss‐
witch.conf(4), resolver(4), host‐
name(5).
Requests for Comments (RFC): 1034,
1035, available online at
available online at
available from the Internet Systems
Consortium at
BIND 9.3 nslookup(1)
