Check contents of /etc/resolv.conf

[yrro]

I've got a machine where resolv.conf was changed from:

# auto-generated by IPA installer
search ipa.example.com
nameserver 127.0.0.1
nameserver ::1

to:

; generated by /usr/sbin/dhclient-script
nameserver 203.0.113.1
nameserver 203.0.113.2
nameserver 203.0.113.3

Maybe ipa-healthcheck could complain if ::1 and 127.0.0.1 are not the only configured nameservers, and if the search list doesn't include the IPA domain?

(In case someone else finds it useful--this particular server is using network-scripts to configure via DHCP; the fix was to add DNS1=127.0.0.1 and DNS2=::1 to /etc/sysconfig/network-scripts/ifcfg-eth0 and reboot).

[rcritten]

That's a great suggestion, thanks.

We'd need to be careful to only apply this when the DNS service is configured and to not assume which addresses are there.

The installer configures 127.0.0.1 if there are any IPv4 addresses and ::1 if any IPv6 in https://github.com/freeipa/freeipa/blob/master/ipaserver/install/bindinstance.py#L1127

[rcritten]

This is somewhat complicated by systemd-resolvd which now owns /etc/resolv.conf. I guess if the file is a symlink to /run/systemd/resolve/stub-resolv.conf then we can executed systemd-resolv --status and scrape for 127.0.0.1.

[yrro]

Since (I think) I filed this issue, FreeIPA has been enhanced to tell NetworkManager to configure the system's DNS to use 127.0.0.1/::1 as its resolver. So probably the original reason I filed this issue is no longer reproducible.

Nonetheless it's probably still useful to have a health check for proper DNS configuration. If you want to check whether resolved 'owns' resolv.conf then the best way to find out is to ask it via D-Bus (check the manager's ResolvConfMode property which can be set to uplink, stub, static if managed, missing if resolv.conf has been deleted, and foreign if resolv.conf is not managed by resolved).

[rcritten]

Yes, D-Bus is a much nicer way to inquire on status, thanks for that!

[rcritten]

I may add this under meta as an informational value.

Simple code for getting this property:

import dbus

bus = dbus.SystemBus()
obj = bus.get_object('org.freedesktop.resolve1',
                     '/org/freedesktop/resolve1')
prop_if = dbus.Interface(obj, 'org.freedesktop.DBus.Properties')
mode = prop_if.Get('org.freedesktop.resolve1.Manager', 'ResolvConfMode')
print(mode)