llwwrreessdd 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.
llwwrreessdd listens for resolver queries on a UDP port on the IPv4 loopback interface, 127.0.0.1. This means that llwwrreessdd 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, llwwrreessdd encodes the answers in the lightweight resolver format and returns them to the client that made the request.
If _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f contains any nnaammeesseerrvveerr entries, llwwrreessdd sends recursive DNS queries to those servers. This is similar to the use of forwarders in a caching name server. If no nnaammeesseerrvveerr entries are present, or if forwarding fails, llwwrreessdd resolves the queries autonomously starting at the root name servers, using a built-in list of root server hints.
-4 Use IPv4 only even if the host machine is capable of IPv6. --44 and --66 are mutually exclusive.
-6 Use IPv6 only even if the host machine is capable of IPv4. --44 and --66 are mutually exclusive.
-c _c_o_n_f_i_g_-_f_i_l_e Use _c_o_n_f_i_g_-_f_i_l_e as the configuration file instead of the default, _/_e_t_c_/_l_w_r_e_s_d_._c_o_n_f. --cc can not be used with --CC.
-C _c_o_n_f_i_g_-_f_i_l_e Use _c_o_n_f_i_g_-_f_i_l_e as the configuration file instead of the default, _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f. --CC can not be used with --cc.
-d _d_e_b_u_g_-_l_e_v_e_l Set the daemon's debug level to _d_e_b_u_g_-_l_e_v_e_l. Debugging traces from llwwrreessdd 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 _s_t_d_e_r_r.
-i _p_i_d_-_f_i_l_e Use _p_i_d_-_f_i_l_e as the PID file instead of the default, _/_v_a_r_/_r_u_n_/_l_w_r_e_s_d_._p_i_d.
-m _f_l_a_g Turn on memory usage debugging flags. Possible flags are _u_s_a_g_e, _t_r_a_c_e, _r_e_c_o_r_d, _s_i_z_e, and _m_c_t_x. These correspond to the ISC_MEM_DEBUGXXXX flags described in _<_i_s_c_/_m_e_m_._h_>.
-n _#_c_p_u_s Create _#_c_p_u_s worker threads to take advantage of multiple CPUs. If not specified, llwwrreessdd 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 _p_o_r_t Listen for lightweight resolver queries on port _p_o_r_t. If not specified, the default is port 921.
-p _p_o_r_t Send DNS lookups to port _p_o_r_t. 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 _s_t_d_o_u_t on exit. Note: This option is mainly of interest to BIND 9 developers and may be removed or changed in a future release.
-t _d_i_r_e_c_t_o_r_y Chroot to _d_i_r_e_c_t_o_r_y after processing the command line arguments, but before reading the configuration file. Warning: This option should be used in conjunction with the --uu option, as chrooting a process running as root doesn't enhance security on most systems; the way cchhrroooott((22)) is defined allows a process with root privileges to escape a chroot jail.
-u _u_s_e_r Setuid to _u_s_e_r after completing privileged operations, such as creating sockets that listen on privileged ports.
-v Report the version number and exit.
_/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f The default configuration file.
_/_v_a_r_/_r_u_n_/_l_w_r_e_s_d_._p_i_d The default process-id file.
nnaammeedd(8), llwwrreess(3), rreessoollvveerr(5).
Internet Systems Consortium