NAME

       nss-resolve, libnss_resolve.so.2 - Hostname resolution via systemd-resolved.service

SYNOPSIS

       libnss_resolve.so.2

DESCRIPTION

       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-resolved(8) 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-resolved(8) for the full list. This duplicates
       the functionality of nss-myhostname(8), 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.

ENVIRONMENT VARIABLES

       $SYSTEMD_NSS_RESOLVE_VALIDATE
           Takes a boolean argument. When false, cryptographic validation of resource records via DNSSEC will be
           disabled. This may be useful for testing, or when system time is known to be unreliable.

           Added in version 250.

       $SYSTEMD_NSS_RESOLVE_SYNTHESIZE
           Takes a boolean argument. When false, synthetic records, e.g. for the local host name, will not be
           returned. See section SYNTHETIC RECORDS in systemd-resolved.service(8) for more information. This may
           be useful to query the "public" resource records, independent of the configuration of the local
           machine.

           Added in version 250.

       $SYSTEMD_NSS_RESOLVE_CACHE
           Takes a boolean argument. When false, the cache of previously queried records will not be used by
           systemd-resolved(8).

           Added in version 250.

       $SYSTEMD_NSS_RESOLVE_ZONE
           Takes a boolean argument. When false, answers using locally registered public LLMNR/mDNS resource
           records will not be returned.

           Added in version 250.

       $SYSTEMD_NSS_RESOLVE_TRUST_ANCHOR
           Takes a boolean argument. When false, answers using locally configured trust anchors will not be
           used.

           Added in version 250.

       $SYSTEMD_NSS_RESOLVE_NETWORK
           Takes a boolean argument. When false, answers will be returned without using the network, i.e. either
           from local sources or the cache in systemd-resolved(8).

           Added in version 250.

EXAMPLE

       Here is an example /etc/nsswitch.conf file that enables nss-resolve correctly:

           passwd:         files systemd
           group:          files [SUCCESS=merge] systemd
           shadow:         files 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

SEE ALSO

       systemd(1), systemd-resolved(8), nss-systemd(8), nss-myhostname(8), nss-mymachines(8), nsswitch.conf(5),
       systemd.syntax(7)

systemd 257.4                                                                                     NSS-RESOLVE(8)