Provided by: unbound_1.6.7-1ubuntu2.6_amd64 
NAME
unbound - Unbound DNS validating resolver 1.6.7.
SYNOPSIS
unbound [-h] [-d] [-p] [-v] [-c cfgfile]
DESCRIPTION
Unbound is a caching DNS resolver.
It uses a built in list of authoritative nameservers for the root zone (.), the so called root hints. On
receiving a DNS query it will ask the root nameservers for an answer and will in almost all cases receive
a delegation to a top level domain (TLD) authoritative nameserver. It will then ask that nameserver for
an answer. It will recursively continue until an answer is found or no answer is available (NXDOMAIN).
For performance and efficiency reasons that answer is cached for a certain time (the answer's
time-to-live or TTL). A second query for the same name will then be answered from the cache. Unbound
can also do DNSSEC validation.
To use a locally running Unbound for resolving put
nameserver 127.0.0.1
into resolv.conf(5).
If authoritative DNS is needed as well using nsd(8), careful setup is required because authoritative
nameservers and resolvers are using the same port number (53).
The available options are:
-h Show the version and commandline option help.
-c cfgfile
Set the config file with settings for unbound to read instead of reading the file at the default
location, /etc/unbound/unbound.conf. The syntax is described in unbound.conf(5).
-d Debug flag: do not fork into the background, but stay attached to the console. This flag will
also delay writing to the log file until the thread-spawn time, so that most config and setup
errors appear on stderr. If given twice or more, logging does not switch to the log file or to
syslog, but the log messages are printed to stderr all the time.
-p Don't use a pidfile. This argument should only be used by supervision systems which can ensure
that only one instance of unbound will run concurrently.
-v Increase verbosity. If given multiple times, more information is logged. This is in addition to
the verbosity (if any) from the config file.
SEE ALSO
unbound.conf(5), unbound-checkconf(8), nsd(8).
AUTHORS
Unbound developers are mentioned in the CREDITS file in the distribution.