NAME
nslookup —
query Internet name servers
interactively
SYNOPSIS
nslookup |
[-option
...]
[host-to-find |
-[server]] |
DESCRIPTION
nslookup is a program to query Internet domain name servers.
nslookup has two modes: interactive and non-interactive.
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.
Non-interactive mode is used to print just the name and requested information
for a host or domain.
ARGUMENTS
Interactive mode is entered in the following cases:
- when no arguments are given (the default name server will
be used),
- when the first argument is a hyphen (‘-’) and
the second argument is the host name or Internet address of a name
server.
Non-interactive mode is used 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 host name or address of a name server.
The options listed under the “
set
” command
below 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
hyphen. For example, to change the default query type to host information, and
the initial timeout to 10 seconds, type:
nslookup -query=hinfo -timeout=10
INTERACTIVE COMMANDS
Commands may be interrupted at any time by typing a control-C. To exit, type a
control-D (
EOF
) or type
exit
.
The command line length must be less than 256 characters. To treat a built-in
command as a host name, precede it with an escape character (‘\’).
N.B.: unrecognized command will be
interpreted as a host name.
-
-
- 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
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 period to the
name.
-
-
- 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't 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). The
name is optional. > and
>> can be used to redirect output in the usual
manner.
-
-
- ls
[option]
domain [>
filename]
-
- ls
[option]
domain [>>
filename]
- List the information available for
domain, optionally creating or appending to
filename. The default output contains host names and
their Internet addresses. Option can be one of the
following:
-
-
- -t
querytype
- lists all records of the specified type (see
querytype below).
-
-
- -a
- lists aliases of hosts in the domain; synonym for
“-t
CNAME
”.
-
-
- -d
- lists all records for the domain; synonym for
“-t
ANY
”.
-
-
- -h
- lists CPU and operating system information for the
domain; synonym for “-t
HINFO
”.
-
-
- -s
- lists well-known services of hosts in the domain;
synonym for “-t
WKS
”.
When output is directed to a file, hash marks are printed for every 50
records received from the server.
-
-
- view
filename
- Sorts and lists the output of previous ls
command(s) with more(1).
-
-
- help
-
- ?
- Prints a brief summary of commands.
-
-
- exit
- Exits the program.
-
-
- set
keyword[=value]
- This command is used to change state information that
affects the lookups. Valid keywords are:
-
-
- all
- Prints the current values of the frequently-used
options to set. Information about the current
default server and host is also printed.
-
-
- class=value
- Change the query class to one of:
-
-
IN
- the 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
- Turn 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]d2
- Turn exhaustive debugging mode on. Essentially all
fields of every packet are printed.
(Default = nod2)
-
-
- domain=name
- Change 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(1),
/etc/resolv.conf, or
LOCALDOMAIN
; abbreviation =
do)
-
-
- srchlist=name1/name2/...
- Change the default domain name to
name1 and the domain search list to
name1, name2, etc. 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(1),
/etc/resolv.conf, or
LOCALDOMAIN
; abbreviation =
srchl)
-
-
- [no]defname
- If set, append the default domain name to a
single-component lookup request (i.e., one that does not contain a
period).
(Default = defname; abbreviation =
[no]defname)
-
-
- [no]search
- If the lookup request contains at least one period but
doesn't end with a trailing period, append the
domain names in the domain search list to the request until an answer
is received.
(Default = search; abbreviation =
[no]sea)
-
-
- port=value
- Change the default TCP/UDP name server port to
value.
(Default = 53; abbreviation = po)
-
-
- querytype=value
-
- type=value
- Change the type of information query to one of:
-
-
A
- the host's Internet address.
-
-
CNAME
- the canonical name for an alias.
-
-
HINFO
- the host CPU and operating system type.
-
-
MINFO
- the mailbox or mail list information.
-
-
MX
- the mail exchanger.
-
-
NS
- the name server for the named zone.
-
-
PTR
- the host name if the query is 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 (ANY
, AXFR
,
MB
, MD
,
MF
, NULL
) are
described in the RFC-1035 document.
(Default = A
; abbreviations =
q, ty)
-
-
- [no]recurse
- Tell the name server to query other servers if it does
not have the information.
(Default = recurse; abbreviation =
[no]rec)
-
-
- retry=number
- Set the number of retries to
number. 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 giving up.
(Default = 4, abbreviation = ret)
-
-
- root=host
- Change the name of the root server to
host. This affects the
“root” command.
(Default = ns.internic.net.; abbreviation =
ro)
-
-
- timeout=number
- Change the initial timeout interval for waiting for a
reply to number seconds. Each retry doubles the
timeout period.
(Default = 5 seconds; abbreviation = ti)
-
-
- [no]vc
- Always 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)
ENVIRONMENT
HOSTALIASES
- file containing host aliases
LOCALDOMAIN
- overrides default domain
FILES
- /etc/resolv.conf
- initial domain name and name server addresses
- $HOME/.nslookuprc
- user's initial options
- /usr/share/misc/nslookup.help
- summary of commands
DIAGNOSTICS
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 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 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.
SEE ALSO
resolver(3),
resolv.conf(5),
named(8)
P.V. Mockapetris,
Domain Names - Concepts and Facilities,
RFC 1034, Nov 1,
1987.
P.V. Mockapetris,
Domain Names - Implementation and Specification,
RFC 1035, Nov 1,
1987.
AUTHORS
Andrew Cherenson