How Do I Identify the Resolver?

spellinator · 10-24-2022, 12:21 PM

Using centOS 7, how do I identify what mechanism is being used to resolve DNS?

I know there's no systemd-resolved.service.
I don't see bind running.

There's an /etc/resolv.conf file.

Is name resolution just built into the kernel?

Thanks!

smallpond · 10-24-2022, 12:45 PM

On my Fedora system:

Code:

grep hosts /etc/nsswitch.conf
hosts:      files myhostname mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns

So it first uses files (/etc/hosts), then checks my hostname, then mdns (avahi), then async DNS (dns.resolve), lastly sync DNS (getaddrinfo) if async is not UNAVAIL.

I don't have bind running, either, but do run systemd. dns.resolve sends queries to the dns server in your /etc/resolv.conf file.

michaelk · 10-24-2022, 12:59 PM

I do not know the exact process but without Network Manager it is dhclient via the dhclient-script. With Network Manager running, it runs dhclient so depending on how networking is configured i.e. if you configured a static DNS or using DHCP it might handle part of the dhclient-script process itself that creates /etc/resolv.conf.

spellinator · 10-24-2022, 01:34 PM

[root@<<REDACTED>> ~]# grep hosts /etc/nsswitch.conf
#hosts: db files nisplus nis dns
hosts: files dns myhostname