systemd nss-resolve 8 nss-resolve libnss_resolve.so.2 Hostname resolution via systemd-resolved.service libnss_resolve.so.2 nss-resolve is a plug-in module for the GNU Name Service Switch (NSS) functionality of the GNU C Library (glibc) enabling it to resolve hostnames via the systemd-resolved8 local network name resolution service. It replaces the nss-dns plug-in module that traditionally resolves hostnames via DNS. To activate the NSS module, add resolve [!UNAVAIL=return] to the line starting with hosts: in /etc/nsswitch.conf. Specifically, it is recommended to place resolve early in /etc/nsswitch.conf's hosts: line. It should be before the files entry, since systemd-resolved supports /etc/hosts internally, but with caching. To the contrary, it should be after mymachines, to give hostnames given to local VMs and containers precedence over names received over DNS. Finally, we recommend placing dns somewhere after resolve, to fall back to nss-dns if systemd-resolved.service is not available. Note that systemd-resolved will synthesize DNS resource records in a few cases, for example for localhost and the current local hostname, see systemd-resolved8 for the full list. This duplicates the functionality of nss-myhostname8, but it is still recommended (see examples below) to keep nss-myhostname configured in /etc/nsswitch.conf, to keep those names resolveable if systemd-resolved is not running. Please keep in mind that nss-myhostname (and nss-resolve) also resolve in the other direction — from locally attached IP addresses to hostnames. If you rely on that lookup being provided by DNS, you might want to order things differently. Communication between nss-resolve and systemd-resolved.service takes place via the /run/systemd/resolve/io.systemd.Resolve AF_UNIX socket. Here is an example /etc/nsswitch.conf file that enables nss-resolve correctly: passwd: compat systemd group: compat [SUCCESS=merge] systemd shadow: compat systemd gshadow: files systemd hosts: mymachines resolve [!UNAVAIL=return] files myhostname dns networks: files protocols: db files services: db files ethers: db files rpc: db files netgroup: nis systemd1, systemd-resolved8, nss-systemd8, nss-myhostname8, nss-mymachines8, nsswitch.conf5