nss-resolve(8) — Linux manual page

NSS-RESOLVE(8)                 nss-resolve                NSS-RESOLVE(8)

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(5)

COLOPHON

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 257~devel                                         NSS-RESOLVE(8)

Pages that refer to this page: systemd.directives(7), systemd.index(7), nss-myhostname(8), nss-mymachines(8), nss-systemd(8), systemd-resolved.service(8)

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