In this article, we will delve into the process of flushing DNS and identifying networking services in Ubuntu 18.04. We’ll explore how to manage your system’s DNS cache, understand the TTL (Time to Live) of a DNS record, and identify the networking services running on your system.
To flush DNS in Ubuntu 18.04, you can recreate the symlink and restart the systemd-resolved service. To identify networking services, you can use the systemctl command.
Understanding DNS Cache
DNS cache refers to the temporary storage of information about previous DNS lookups on a machine’s operating system or web browser. Flushing, or clearing, the DNS cache can help resolve network related issues. Ubuntu 18.04, like many other systems, uses a network management daemon called NetworkManager.
Flushing DNS Cache in Ubuntu 18.04
To flush the DNS cache in Ubuntu 18.04, you will need to follow these steps:
Step 1: Check for Existing Symlink
Check if the symlink /etc/systemd/system/dbus-org.freedesktop.resolve1.service exists. This can be done by running the following command:
ls -l /etc/systemd/system/dbus-org.freedesktop.resolve1.serviceIf the symlink does not exist, you will need to recreate it.
Step 2: Recreate the Symlink
To recreate the symlink, run the following command:
sudo ln -sf /lib/systemd/system/systemd-resolved.service /etc/systemd/system/dbus-org.freedesktop.resolve1.serviceIn this command, ln is used to create links between files. The -s option creates a symbolic link, and -f forces the creation of the link by removing existing destination files.
Step 3: Restart the systemd-resolved Service
Finally, restart the systemd-resolved service to flush the DNS caches:
sudo systemctl restart systemd-resolved.serviceIn this command, systemctl is a command to introspect and control the state of the “systemd” system and service manager. restart is the option to restart a running service.
Determining the TTL of a DNS Record
To determine the TTL of a DNS record or the DNS cache, you can use the dig command from the dnsutils package. If you don’t have it installed, you can install it by running:
sudo apt install dnsutilsOnce installed, you can use the dig command followed by the domain name to retrieve the DNS information, including the TTL. For example, to check the TTL of the askubuntu.com domain, run:
dig askubuntu.comThe output will include an “ANSWER SECTION” that shows the TTL value.
Identifying Networking Services in Ubuntu 18.04
Popular networking providers for Ubuntu 18.04 include NetworkManager, systemd-networkd, and ifupdown. These providers offer different ways to manage network configurations on Ubuntu. You can identify which service is running on your system by using the following command:
systemctl | grep -E 'NetworkManager|systemd-networkd|ifupdown'This command uses grep to search for the specified networking services in the output of systemctl.
In conclusion, managing DNS cache and identifying networking services are essential tasks for system administrators. Understanding these processes can help you troubleshoot network issues and maintain the performance of your Ubuntu 18.04 system.
There is no set frequency for flushing the DNS cache. It is recommended to flush the cache whenever you encounter network-related issues or if you have made changes to your DNS settings.
Yes, you can flush the DNS cache without restarting the service by running the command sudo systemd-resolve --flush-caches. This command will clear the DNS cache without the need for a service restart.
To check the current DNS cache size, you can use the command sudo systemd-resolve --statistics. This will display various statistics related to the DNS cache, including the cache size.
To disable DNS caching in Ubuntu 18.04, you can edit the /etc/systemd/resolved.conf file and uncomment the line #DNSStubListener=yes by removing the # symbol. Save the file and restart the systemd-resolved service using sudo systemctl restart systemd-resolved.service.
To identify the IP address of a specific networking service, you can use the systemctl status <service-name> command. Replace <service-name> with the name of the networking service you want to check. The output will include information about the service, including its IP address if applicable.
You can determine the version of NetworkManager, systemd-networkd, or ifupdown installed on your Ubuntu 18.04 system by running the command dpkg -l | grep -E 'network-manager|systemd-networkd|ifupdown'. This will display the installed version of the respective networking service.
