nss-resolve

systemd
nss-resolve 8
nss-resolve libnss_resolve.so.2 Hostname resolution via `systemd-resolved.service`

`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 adresses to hostnames. If you rely on that lookup being provided by DNS, you might want to order things differently.

## Example

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

## See Also

systemd 1, systemd-resolved 8, nss-systemd 8, nss-myhostname 8, nss-mymachines 8, nsswitch.conf 5