unbound - Unbound DNS validating resolver 1.13.1.
unbound [-h] [-d] [-p] [-v] [-c cfgfile]
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
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:
- Show the version number and commandline option help, and exit.
- -c cfgfile
- Set the config file with settings for unbound to read instead of reading the file at the default location, /var/unbound/etc/unbound.conf. The syntax is described in unbound.conf(5).
- 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.
- 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.
- Increase verbosity. If given multiple times, more information is logged. This is in addition to the verbosity (if any) from the config file.
- Show the version number and build options, and exit.
unbound.conf(5), unbound-checkconf(8), nsd(8).
Unbound developers are mentioned in the CREDITS file in the distribution.