systemd-resolved.service, systemd-resolved - Network Name Resolution
systemd-resolved is a system service that provides network name
resolution to local applications. It implements a caching and
validating DNS/DNSSEC stub resolver, as well as an LLMNR resolver and
responder. In addition it maintains the
/run/systemd/resolve/resolv.conf file for compatibility with
traditional Linux programs. This file may be symlinked from
The glibc NSS module nss-resolve(8) is required to permit glibc's NSS
resolver functions to resolve host names via systemd-resolved.
The DNS servers contacted are determined from the global settings in
/etc/systemd/resolved.conf, the per-link static settings in
/etc/systemd/network/*.network files, and the per-link dynamic settings
received over DHCP. See resolved.conf(5) and systemd.network(5) for
details. To improve compatibility, /etc/resolv.conf is read in order to
discover configured system DNS servers, but only if it is not a symlink
to /run/systemd/resolve/resolv.conf (see above).
systemd-resolved synthesizes DNS RRs for the following cases:
o The local, configured hostname is resolved to all locally
configured IP addresses ordered by their scope, or -- if none are
configured -- the IPv4 address 127.0.0.2 (which is on the local
loopback) and the IPv6 address ::1 (which is the local host).
o The hostname "localhost" (as well as any hostname ending in
".localhost", ".localdomain" or equal to "localdomain") is resolved
to the IP addresses 127.0.0.1 and ::1.
o The hostname "gateway" is resolved to all current default routing
gateway addresses, ordered by their metric. This assigns a stable
hostname to the current gateway, useful for referencing it
independently of the current network configuration state.
o The mappings defined in /etc/hosts are resolved to their configured
addresses and back.
Lookup requests are routed to the available DNS servers and LLMNR
interfaces according to the following rules:
o Lookups for the special hostname "localhost" are never routed to
the network. (A few other, special domains are handled the same
o Single-label names are routed to all local interfaces capable of IP
multicasting, using the LLMNR protocol. Lookups for IPv4 addresses
are only sent via LLMNR on IPv4, and lookups for IPv6 addresses are
only sent via LLMNR on IPv6. Lookups for the locally configured
host name and the "gateway" host name are never routed to LLMNR.
o Multi-label names are routed to all local interfaces that have a
DNS sever configured, plus the globally configured DNS server if
there is one. Address lookups from the link-local address range are
never routed to DNS.
If lookups are routed to multiple interfaces, the first successful
response is returned (thus effectively merging the lookup zones on all
matching interfaces). If the lookup failed on all interfaces, the last
failing response is returned.
Routing of lookups may be influenced by configuring per-interface
domain names. See systemd.network(5) for details. Lookups for a
hostname ending in one of the per-interface domains are exclusively
routed to the matching interfaces.
Note that /run/systemd/resolve/resolv.conf should not be used directly
by applications, but only through a symlink from /etc/resolv.conf.
See the resolved D-Bus API Documentation for information about the
APIs systemd-resolved provides.
systemd(1), resolved.conf(5), dnssec-trust-anchors.d(5), nss-
resolve(8), systemd-resolve(1), resolv.conf(5), hosts(5),
1. resolved D-Bus API Documentation
systemd 229 SYSTEMD-RESOLVED.SERVICE(8)
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