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NAME | SYNOPSIS | DESCRIPTION | ENVIRONMENT VARIABLES | EXAMPLE | SEE ALSO | COLOPHON |
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NSS-RESOLVE(8) nss-resolve 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-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.
$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.
$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.
$SYSTEMD_NSS_RESOLVE_CACHE
Takes a boolean argument. When false, the cache of previously
queried records will not be used by systemd-resolved.
$SYSTEMD_NSS_RESOLVE_ZONE
Takes a boolean argument. When false, answers using locally
registered public LLMNR/mDNS resource records will not be
returned.
$SYSTEMD_NSS_RESOLVE_TRUST_ANCHOR
Takes a boolean argument. When false, answers using locally
configured trust anchors will not be used.
$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.
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
systemd(1), systemd-resolved(8), nss-systemd(8),
nss-myhostname(8), nss-mymachines(8), nsswitch.conf(5),
systemd.syntax(5)
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 2022-12-17. (At that
time, the date of the most recent commit that was found in the
repository was 2022-12-16.) 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 252 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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