NAME
nslookup — query name servers interactively
SYNOPSIS
nslookup
[-option ...]
host-to-find
[server]
nslookup
[-option ...]
[-
[server]]
DESCRIPTION
nslookup
is a program to query Internet domain name servers.
nslookup
has been extended to follow the configured name resolution
algorithm of the host and to query
NIS,
as well as, DNS and
host tables.
Both an interactive and non-interactive mode are available with
nslookup.
Interactive mode allows the user to query a name server for
information about various hosts and domains, or print a list of hosts
in the domain.
Non-interactive mode is used to query a name server for
information about one host or domain.
By default,
nslookup
accesses name services for name and address resolution based
on the policy information obtained from the switch configuration file
/etc/nsswitch.conf.
When the policy is set to use NIS or
/etc/hosts
first, or when DNS
is first but unavailable, then
nslookup
will only provide a limited
command set (a
help
command while in this situation will show what actions are possible when
querying NIS or
/etc/hosts).
To override the switch policy and query DNS servers directly,
the
server
command can be used to specify a nameserver. This same overriding of
the switch policy can also be done by providing a nameserver as the second
argument on the command line. In this case,
nslookup
will ignore the switch policy and directly query nameservers, until a
reset
command is issued. Whenever an action is taken that causes the
switch policy to be overridden, a warning message is displayed.
Note, NIS+ is not supported by
nslookup.
If the hosts source
nisplus
is found in the
/etc/nsswitch.conf
file. It will be ignored.
ARGUMENTS
Interactive mode is entered in the following cases:
The first argument is a hyphen
(-).
The optional second argument is a host name
or Internet (IP) address of a name server.
Non-interactive mode is used when the name of the host
to be looked up is given as the first argument.
The optional second argument is a host name
or Internet address of a name server.
Options listed under the
set
command below can be specified one per line in the
.nslookuprc
file in the user's home directory.
Alternatively, these options may be specified on the command line
by prefixing them with a hyphen and they must precede other command line
arguments.
For example, to change the default query type to host information,
and the initial timeout to 10 seconds, type:
nslookup -query=hinfo -timeout=10
The command line option
-swdebug
may be used to debug syntactic errors
in the switch configuration file. This option turns on tracing during
initialization, causing the switch module to print out a trace of
the scan and parse actions on the "hosts" entry (see
nsswitch.conf(4))
in the
/etc/nsswitch.conf
file.
Interactive Commands
Commands can be interrupted at any time
by using the interrupt character.
To exit, type a Ctrl-D
(EOF)
or type
exit.
To treat a built-in command as a host name,
precede it with an escape character
(\).
When using
NIS
or the host table, only host names and Internet addresses
are allowed as commands.
An unrecognized command is 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,
one or more domains are appended to the name
(this behavior depends on the state of the
set
options
domain,
srchlist,
defname,
and
search).
Answers from a name server's cache are labeled ``non-authoritative.''
- 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. When
server
is used while the current name service being pointed to is either
NIS
or
/etc/hosts,
then the switch policy will be overridden until
a
reset
is issued.
- root
Changes the default server to the server
for the root of the domain name space.
Currently, the host
ns.nic.ddn.mil
is used
(this command is a synonym for
lserverns.nic.ddn.mil).
The name of the root server can be changed with the
set root
command.
- policy
Prints out the policy read from the switch configuration file. The
number of name services specified 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 the four positions within the square
brackets. The order of the statuses are: SUCCESS, NOTFOUND, UNAVAIL and
TRYAGAIN. The two actions of the criteria are represented by the two
possible letters used in the four status positions:
R
for return and
C
for continue.
However, if no criteria is specified between two sources, then the default
actions are assigned to the statuses:
SUCCESS= return
NOTFOUND= continue
UNAVAIL= continue
TRYAGAIN= continue
- 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.
>
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,
#
characters are printed for every 50 records received from the server.
- view filename
Sorts and lists the output of previous
ls
command(s) using
more
(see
more(1)).
- help
- ?
Prints a brief summary of commands.
- exit
Exits the program.
- reset
Returns to the use of the configured name service switch policy
and resets to use the original nameservers.
- 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 various options to
set.
Information about the current default server and host is also printed.
- cl[ass]=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)
- [no]deb[ug]
Turn debugging mode on.
More information is printed about the packet
sent to the server and the resulting answer.
(Default =
nodebug)
- [no]d2
Turn exhaustive debugging mode on.
Essentially all fields of every packet are printed.
(Default =
nod2)
- [no]def[name]
If set,
append the default domain name to a single-component lookup request
(i.e., one that does not contain a period character).
(Default =
defname)
- do[main]=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,
/etc/resolv.conf
or
LOCALDOMAIN)
- [no]ig[nore]
Ignore truncation errors.
(Default =
noignore)
- q[uerytype]=value
- ty[pe]=value
Change the type of information returned from a query to one of:
- A
Host's Internet address
- ANY
All types of data
- CNAME
Canonical name for an alias
- GID
Group ID
- HINFO
Host CPU and operating system type
- MB
Mailbox domain name
- MG
Mail group member
- MINFO
Mailbox or mail list information
- MR
Mail rename domain name
- MX
Mail exchanger
- NS
Name server for the named zone
- PTR
Host name if the query is an Internet address,
otherwise the pointer to other information.
- SOA
Start of authority record
- TXT
Text information
- UID
User ID
- UINFO
User information
- WKS
Well-known service description
- po[rt]=value
Change the default
TCP/UDP
name server port to
value.
(Default = 53)
- [no]rec[urse]
Tell the name server to query other servers
if it does not have the information.
(Default =
recurse)
- ret[ry]=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)
- ro[ot]=host
Change the name of the root server to
host.
This affects the
root
command.
(Default =
ns.nic.ddn.mil)
- [no]sea[rch]
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.
See
hostname(5).
(Default =
search)
- srchl[ist]=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,
/etc/resolv.conf
or
LOCALDOMAIN)
- [no]swtr[ace]
When set, this flag causes
nslookup
to print out information about the
sources used for resolving a name or an address lookup. This flag
traces the behavior generated by the switch policy.
(Default =
noswtrace)
- t[imeout]=number
Change the initial timeout interval for waiting for a reply to
number
seconds.
Each retry doubles the timeout period.
(Default = 5 seconds)
- [no]v[c]
Always use a virtual circuit when sending requests to the server.
(Default =
novc)
DIAGNOSTICS
If the lookup request was not successful, an error message is printed.
Possible errors are:
- Time-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 server could not be made
at the present time.
- 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.
AUTHOR
nslookup
was developed by the University of California, Berkeley.
FILES
- /etc/resolv.conf
Initial domain name and name server addresses
- $HOME/.nslookuprc
User's initial options
