lwresd - lightweight resolver daemon

lwresd is the daemon providing name lookup services to clients that use the BIND 9 lightweight resolver library. It is essentially a stripped-down, caching-only name server that answers queries using the BIND 9 lightweight resolver protocol rather than the DNS protocol.

lwresd listens for resolver queries on a UDP port on the IPv4 loopback interface, 127.0.0.1. This means that lwresd can only be used by processes running on the local machine. By default UDP port number 921 is used for lightweight resolver requests and responses.

Incoming lightweight resolver requests are decoded by the server which then resolves them using the DNS protocol. When the DNS lookup completes, lwresd encodes the answers in the lightweight resolver format and returns them to the client that made the request.

If /etc/resolv.conf contains any nameserver entries, lwresd sends recursive DNS queries to those servers. This is similar to the use of forwarders in a caching name server. If no nameserver entries are present, or if forwarding fails, lwresd resolves the queries autonomously starting at the root name servers, using a built-in list of root server hints.

-C config-file

Use config-file as the configuration file instead of the default, /etc/resolv.conf.

-d debug-level

Set the daemon's debug level to debug-level. Debugging traces from lwresd become more verbose as the debug level increases.

-f

Run the server in the foreground (i.e. do not daemonize).

-g

Run the server in the foreground and force all logging to stderr.

-n #cpus

Create #cpus worker threads to take advantage of multiple CPUs. If not specified, lwresd will try to determine the number of CPUs present and create one thread per CPU. If it is unable to determine the number of CPUs, a single worker thread will be created.

-P port

Listen for lightweight resolver queries on port port. If not specified, the default is port 921.

-p port

Send DNS lookups to port port. If not specified, the default is port 53. This provides a way of testing the lightweight resolver daemon with a name server that listens for queries on a non-standard port number.

-s

Write memory usage statistics to stdout on exit. Note: This option is mainly of interest to BIND 9 developers and may be removed or changed in a future release.

-t directory

chroot() to directory after processing the command line arguments, but before reading the configuration file. Warning: This option should be used in conjunction with the -u option, as chrooting a process running as root doesn't enhance security on most systems; the way chroot() is defined allows a process with root privileges to escape a chroot jail.

-u user

setuid() to user after completing privileged operations, such as creating sockets that listen on privileged ports.

-v

Report the version number and exit.

/etc/resolv.conf

The default configuration file.

/var/run/lwresd.pid

The default process-id file.

named(8), lwres(3), resolver(5).

Internet Systems Consortium