Samba AD DC Malfunction -> Stopping slapd Resolved the Issue

On Ubuntu 18, the samba-ad-dc service was running and was being used from a Synology NAS,

but after updating Ubuntu 18, I tried to update the domain information and encountered an error saying "No trusted domain controller found."

As a test, I tried to connect from another AD client (Mac), and an error like "Error: Connection failed to the directory server. (2100)" appeared.

When I checked the logs in /var/log/samba/, I found NT_STATUS_ADDRESS_ALREADY_ASSOCIATED (I forgot the file name).

As a test, on the AD server, I checked the status of slapd with /var/log/samba# sudo service slapd status

● slapd.service - LSB: OpenLDAP standalone server (Lightweight Directory Access Protocol)
Loaded: loaded (/etc/init.d/slapd; generated)
Active: active (running) since Tue 2018-12-04 18:56:39 JST; 2h 19min ago
Docs: man:systemd-sysv-generator(8)

Since it was running actively,

sudo service slapd stop

sudo service samba-ad-dc stop

sudo service samba-ad-dc status

After stopping the samba-ad-dc and slapd services, samba-ad-dc worked properly.

(Using sudo systemctl stop ... might be recommended)

To stop the service

sudo systemctl disable slapd.service

Restart and verify.