DNS - Revision history

Pio2pio: /* AWS */

2025-08-26T21:09:58Z

AWS

@@ Line 121: / Line 121: @@
 </source>
-= AWS =
+== DNS Management in Ubuntu 24.04: systemd-resolved vs. resolvconf ==
-*[https://aws.amazon.com/blogs/security/simplify-dns-management-in-a-multiaccount-environment-with-route-53-resolver/ DNS resolver in multi-accout environment | shared dns-resolver ] 28 MAY 2019
+On modern Ubuntu systems, including 24.04, <code>systemd-resolved</code> has become the primary service for managing DNS resolution. It replaces the legacy <code>resolvconf</code> framework as the default, offering a more robust and integrated solution. For advanced users, the key takeaway is the shift in tooling and configuration from the traditional <code>/etc/resolv.conf</code> file to the <code>resolvectl</code> command and its integration with systemd.
 = References =
 *[https://en.wikipedia.org/wiki/List_of_DNS_record_types List of DNS record types] Wikipedia

Pio2pio: /* flush dns */

2022-10-21T14:08:27Z

flush dns

← Older revision		Revision as of 16:08, 21 October 2022
Line 69:		Line 69:
	resolvectl statistics # show statistics, the same output as 'systemd-resolve --statistics'		resolvectl statistics # show statistics, the same output as 'systemd-resolve --statistics'
	sudo systemd-resolve --statistics # or --reset-statistics - resets resolver statistics		sudo systemd-resolve --statistics # or --reset-statistics - resets resolver statistics
	sudo systemd-resolve --flush-caches # Flush Ubuntu DNS Cache
			sudo systemd-resolve --flush-caches # Flush Ubuntu DNS Cache - Ubuntu <22.04 (old)
			resolvectl flush-caches # Flush Ubuntu DNS Cache - Ubuntu 22.04


	sudo systemctl restart nscd # Other distros, eg arch Linux		sudo systemctl restart nscd # Other distros, eg arch Linux
Line 75:		Line 78:
	# Resolve a name without using local cache		# Resolve a name without using local cache
	sudo systemd-resolve --flush-caches		sudo systemd-resolve --flush-caches
			resolvectl flush-caches

	systemd-resolve --statistics \| grep 'Current Cache Size' # -> Current Cache Size: 0		systemd-resolve --statistics \| grep 'Current Cache Size' # -> Current Cache Size: 0
	dig +short tvp.info @8.8.8.8		dig +short tvp.info @8.8.8.8

Pio2pio: /* flush dns */

2021-05-22T10:06:09Z

flush dns

← Older revision		Revision as of 12:06, 22 May 2021
Line 83:		Line 83:
	# Display cached dns entries		# Display cached dns entries
	sudo killall -USR1 systemd-resolved # it doesn't stop the service, it tells systemd-resolved to write all the current cache entries to the system log		sudo killall -USR1 systemd-resolved # it doesn't stop the service, it tells systemd-resolved to write all the current cache entries to the system log
	journalctl -u systemd-resolved # ~~read~~ the ~~logs~~		journalctl -u systemd-resolved # list the cached entries from the log

	## Oneliner		## Oneliner

Pio2pio: /* flush dns */

2021-05-22T10:05:39Z

flush dns

← Older revision		Revision as of 12:05, 22 May 2021
Line 67:		Line 67:

	# Ubuntu 18.04, 20.04		# Ubuntu 18.04, 20.04
	sudo systemd-resolve --statistics # or --reset-statistics - resets resolver statistics		resolvectl statistics # show statistics, the same output as 'systemd-resolve --statistics'
			sudo systemd-resolve --statistics # or --reset-statistics - resets resolver statistics
	sudo systemd-resolve --flush-caches # Flush Ubuntu DNS Cache		sudo systemd-resolve --flush-caches # Flush Ubuntu DNS Cache

	sudo systemctl restart nscd # Other distros, eg arch Linux		sudo systemctl restart nscd # Other distros, eg arch Linux

	# ~~resolve~~ a name without using local cache		# Resolve a name without using local cache
	sudo systemd-resolve --flush-caches		sudo systemd-resolve --flush-caches
	systemd-resolve --statistics \| grep 'Current Cache Size' # -> Current Cache Size: 0		systemd-resolve --statistics \| grep 'Current Cache Size' # -> Current Cache Size: 0
Line 79:		Line 80:
	dig +short tvp.info		dig +short tvp.info
	systemd-resolve --statistics \| grep 'Current Cache Size' # -> Current Cache Size: 1		systemd-resolve --statistics \| grep 'Current Cache Size' # -> Current Cache Size: 1

			# Display cached dns entries
			sudo killall -USR1 systemd-resolved # it doesn't stop the service, it tells systemd-resolved to write all the current cache entries to the system log
			journalctl -u systemd-resolved # read the logs

			## Oneliner
			sudo killall -USR1 systemd-resolved; journalctl -u systemd-resolved --since "5s ago"
	</source>		</source>

Pio2pio: /* flush dns */

2021-05-22T09:28:03Z

flush dns

← Older revision		Revision as of 11:28, 22 May 2021
Line 72:		Line 72:
	sudo systemctl restart nscd # Other distros, eg arch Linux		sudo systemctl restart nscd # Other distros, eg arch Linux

	# resolve a name without ~~caching~~		# resolve a name without using local cache
	sudo systemd-resolve --flush-caches		sudo systemd-resolve --flush-caches
	systemd-resolve --statistics \| grep 'Current Cache Size' # -> Current Cache Size: 0		systemd-resolve --statistics \| grep 'Current Cache Size' # -> Current Cache Size: 0

Pio2pio: /* flush dns */

2021-05-22T09:27:43Z

flush dns

← Older revision		Revision as of 11:27, 22 May 2021
Line 71:		Line 71:

	sudo systemctl restart nscd # Other distros, eg arch Linux		sudo systemctl restart nscd # Other distros, eg arch Linux

			# resolve a name without caching
			sudo systemd-resolve --flush-caches
			systemd-resolve --statistics \| grep 'Current Cache Size' # -> Current Cache Size: 0
			dig +short tvp.info @8.8.8.8
			systemd-resolve --statistics \| grep 'Current Cache Size' # -> Current Cache Size: 0
			dig +short tvp.info
			systemd-resolve --statistics \| grep 'Current Cache Size' # -> Current Cache Size: 1
	</source>		</source>

Pio2pio: /* Netplan */

2021-05-04T09:49:43Z

Netplan

← Older revision		Revision as of 11:49, 4 May 2021
Line 95:		Line 95:
	addresses: [8.8.8.8, 8.8.4.4]		addresses: [8.8.8.8, 8.8.4.4]

			# Using this method you’ll lose the Network Manager GUI and network icon and let Netplan to manage all devices
	sudo netplan apply		sudo netplan apply
	systemd-resolve --status \| grep 'DNS Servers' -A2		systemd-resolve --status \| grep 'DNS Servers' -A2

Pio2pio: /* Netplan */

2021-05-04T09:48:23Z

Netplan

@@ Line 83: / Line 83: @@
 <source lang=bash>
 sudo netplan apply
 systemd-resolve --status | grep 'DNS Servers' -A2

Pio2pio: /* AWS */

2021-05-04T09:45:59Z

AWS

← Older revision		Revision as of 11:45, 4 May 2021
Line 71:		Line 71:

	sudo systemctl restart nscd # Other distros, eg arch Linux		sudo systemctl restart nscd # Other distros, eg arch Linux
			</source>

			= Netplan =
			Netplan is the default network management tool on Ubuntu 18.04, replacing the /etc/resolv.conf and /etc/network/interfaces configuration files that have been used to configure the network in the previous Ubuntu versions.


			Back in the days, whenever you wanted to configure DNS resolvers in Linux you would simply open the /etc/resolv.conf file, edit the entries, save the file and you are good to go. This file still exists but it is a symlink controlled by the systemd-resolved service and should not be edited manually.


			{{Note\|Info As of 18/05/2020 Network Manager doesn’t respect the Netplan option nameservers: addresses [8.8.8.8,8.8.4.4] option even when you specify dhcp4-overrides: use-dns: false it still uses (and give priority to) the default DHCP DNS servers. This renders any custom DNS servers redundant. The only way around this AFAIK is to specify the Ethernet connection as static.}}

			<source lang=bash>
			sudo netplan apply
			systemd-resolve --status \| grep 'DNS Servers' -A2
	</source>		</source>

Pio2pio: /* flush dns */

2020-10-23T07:54:41Z

flush dns

← Older revision		Revision as of 09:54, 23 October 2020
Line 65:		Line 65:
	sudo systemctl is-active systemd-resolved.service		sudo systemctl is-active systemd-resolved.service
	# -> active		# -> active
	# Ubuntu 18.04
			# Ubuntu 18.04, 20.04
			sudo systemd-resolve --statistics # or --reset-statistics - resets resolver statistics
	sudo systemd-resolve --flush-caches # Flush Ubuntu DNS Cache		sudo systemd-resolve --flush-caches # Flush Ubuntu DNS Cache
	~~sudo systemd-resolve --statistics~~
	~~# --reset-statistics Reset resolver statistics~~
	sudo systemctl restart nscd # Other distros, eg arch Linux		sudo systemctl restart nscd # Other distros, eg arch Linux
	</source>		</source>