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   systemd-resolved.service    ( 8 )

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Описание (Description)

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 and MulticastDNS resolver and responder. Local applications may submit network name resolution requests via three interfaces:

• The native, fully-featured API systemd-resolved exposes on the bus, see org.freedesktop.resolve1(5) and org.freedesktop.LogControl1(5) for details. Usage of this API is generally recommended to clients as it is asynchronous and fully featured (for example, properly returns DNSSEC validation status and interface scope for addresses as necessary for supporting link-local networking).

• The glibc getaddrinfo(3) API as defined by RFC3493[1] and its related resolver functions, including gethostbyname(3). This API is widely supported, including beyond the Linux platform. In its current form it does not expose DNSSEC validation status information however, and is synchronous only. This API is backed by the glibc Name Service Switch (nss(5)). Usage of the glibc NSS module nss-resolve(8) is required in order to allow glibc's NSS resolver functions to resolve hostnames via systemd-resolved.

• Additionally, systemd-resolved provides a local DNS stub listener on IP address 127.0.0.53 on the local loopback interface. Programs issuing DNS requests directly, bypassing any local API may be directed to this stub, in order to connect them to systemd-resolved. Note however that it is strongly recommended that local programs use the glibc NSS or bus APIs instead (as described above), as various network resolution concepts (such as link-local addressing, or LLMNR Unicode domains) cannot be mapped to the unicast DNS protocol.

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 (in case systemd-networkd.service(8) is used), the per-link dynamic settings received over DHCP, information provided via resolvectl(1), and any DNS server information made available by other system services. See resolved.conf(5) and systemd.network(5) for details about systemd's own configuration files for DNS servers. 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/stub-resolv.conf, /usr/lib/systemd/resolv.conf or /run/systemd/resolve/resolv.conf (see below).