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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.
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.
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
systemd(1), systemd-resolved(8), nss-systemd(8),
nss-myhostname(8), nss-mymachines(8), nsswitch.conf(5),
systemd.syntax(7)
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 2025-02-02. (At that
time, the date of the most recent commit that was found in the
repository was 2025-02-02.) 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 258~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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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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