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 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.
Here is an example /etc/nsswitch.conf
file that enables nss-resolve
correctly:
passwd: compat systemd
group: compat systemd
shadow: compat
hosts: mymachines resolve [!UNAVAIL=return] myhostname files dns
networks: files
protocols: db files
services: db files
ethers: db files
rpc: db files
netgroup: nis