Linux drop dns cache

How To Flush Linux / UNIX DNS Cache

I ‘m on a Dial UP Internet connection under Linux and frequent dial up disconnection causing dns problems. How do I flush DNS cache under UNIX / Linux distribution using a shell prompt?

Under MS-Windows you can use the ipconfig command to flush dns cache. However, Linux and UNIX provides various ways to flush cache. Linux can run nscd or BIND or dnsmasq as the name service caching daemon. Large and work-group servers may use BIND or dnsmasq as a dedicated caching server to speed up queries.

HowTo: Flush nscd dns cache

Nscd caches libc-issued requests to the Name Service. If retrieving NSS data is fairly expensive, nscd is able to speed up consecutive access to the same data dramatically and increase overall system performance. Just restart nscd:
$ sudo /etc/init.d/nscd restart
OR
# service nscd restart
OR
# service nscd reload
This daemon provides a cache for the most common name service requests. The default configuration file, /etc/nscd.conf, determines the behavior of the cache daemon.

Flush dnsmasq dns cache

dnsmasq is a lightweight DNS, TFTP and DHCP server. It is intended to provide coupled DNS and DHCP service to a LAN. Dnsmasq accepts DNS queries and either answers them from a small, local, cache or forwards them to a real, recursive, DNS server. This software is also installed many cheap routers to cache dns queries. Just restart the dnsmasq service to flush out dns cache:
$ sudo /etc/init.d/dnsmasq restart
OR
# service dnsmasq restart

• No ads and tracking
• In-depth guides for developers and sysadmins at Opensourceflare✨
• Join my Patreon to support independent content creators and start reading latest guides:
  • How to set up Redis sentinel cluster on Ubuntu or Debian Linux
  • How To Set Up SSH Keys With YubiKey as two-factor authentication (U2F/FIDO2)
  • How to set up Mariadb Galera cluster on Ubuntu or Debian Linux
  • A podman tutorial for beginners – part I (run Linux containers without Docker and in daemonless mode)
  • How to protect Linux against rogue USB devices using USBGuard

Join Patreon ➔

Flush caching BIND server dns cache

A caching BIND server obtains information from another server (a Zone Master) in response to a host query and then saves (caches) the data locally. All you have to do is restart bind to clear its cache:
# /etc/init.d/named restart
You can also use rndc command as follows flush out all cache:
# rndc restart
OR
# rndc exec
BIND v9.3.0 and above will support flushing all of the records attached to a particular domain name with rndc flushname command. In this example flush all records releated to cyberciti.biz domain:
# rndc flushname cyberciti.biz
It is also possible to flush out BIND views. For example, lan and wan views can be flushed using the following command:
# rndc flush lan
# rndc flush wan

A note about Mac OS X Unix users

Type the following command as root user:
# dscacheutil -flushcache
OR
$ sudo dscacheutil -flushcache
If you are using OS X 10.5 or earlier try the following command:
lookupd -flushcache

A note about /etc/hosts file

/etc/hosts act as the static table lookup for hostnames. You need to remove and/or update records as per your requirements under Unix like operating systems:
# vi /etc/hosts
Sample outputs:

See also:

Related: Windows Vista / XP Flush DNS Cache with ipconfig Command

🐧 Get the latest tutorials on Linux, Open Source & DevOps via

Источник

Как очистить / сбросить кеш DNS в Linux

В некоторых случаях вам трудно добраться до некоторых сайтов из-за проблемы с DNS, возможно, ваш локальный DNS-кеш поврежден.

Для такой ситуации вам необходимо перезапустить службу кэширования DNS операционной системы.

Кэш-память DNS для системы доменных имен – это временная база данных, которая поддерживается операционной системой компьютера, которая содержит IP-адрес сайтов, которые вы недавно просматривали.

См. Ниже список основных серверов кэширования DNS, используемых в дистрибутиве Linux.

• nscd DNS cache
• dnsmasq dns cache
• BIND server dns cache

nscd DNS Cache: nscd – демон кэша службы имен, Nscd – это демон, который обеспечивает кэш для наиболее распространенных запросов службы имен.

Файл конфигурации по умолчанию, /etc/nscd.conf

dnsmasq DNS Cache: Dnsmasq – легкий, небольшой в размере, простой в настройке, DNS-сервер и DHCP-сервер.

Он предназначен для предоставления DNS и опционально DHCP для небольшой сети и подходит для маршрутизаторов с ограниченным доступом и брандмауэров.

Он может обслуживать имена локальных машин, которые не входят в глобальный DNS.

Он предназначен для использования в персональных компьютерах и небольших сетях, а не для больших сетей.

BIND Server DNS Cache: BIND означает «Berkeley Internet Name Domain».

Наиболее широко используемое программное обеспечение сервера имен, BIND – это программное обеспечение с открытым исходным кодом, которое реализует протоколы доменных имен (DNS) для Интернета.

BIND на сегодняшний день является наиболее широко используемым программным обеспечением DNS в Интернете, обеспечивая надежную и стабильную платформу.

1) Очистить кеш DNS на Ubuntu / Debian / LinuxMint

Используйте приведенную ниже команду для очистки кеша DNS в системах Ubuntu / Debian / Mint.

2) Сброс кеша dns сервера BIND

Используйте приведенную ниже команду для сброса кеша BIND сервера dns

3) Очистить кэш nscd DNS

Используйте команду ниже:

4) Очистить dnsmasq dns кэш

Используйте приведенную ниже команду для стирания кеша dnsmasq server dns

5) Очистка кеша dns в Windows

Используйте приведенную ниже команду для очистки кеша dns в Windows:

Источник

How to Flush the DNS Cache on Ubuntu

The DNS or the Domain Name Server can be characterized as the most essential part of your link to the internet. The DNS translates the domain names to and from the IP addresses so that we don’t need to remember or keep a list of all the IP addresses of the websites we ever want to access. Our systems also maintain a list of DNS records so that we can access our frequently visited websites faster through quick resolution of IP addresses. This cache on our system needs to be flushed from time to time. This is required because websites may change their addresses time and again, so it is a good idea to avoid IP conflict by clearing the cache. Flushing the cache is also a good way to clear unnecessary data residing on our systems.

So let us see how we can flush the DNS cache on our Ubuntu Systems.

We have executed the commands and procedures mentioned in this article on an Ubuntu 18.04 LTS system. Since we are using the Linux command line-the Terminal to flush the cache, you can open it through the system Dash or the CTRL+ALT+T shortcut.

Method 1: Using systemd-resolve to flush DNS-Cache

Most Ubuntu and Debian systems are running the systemd-resolve daemon. Your system already uses it for a lot of things. So let us use it for flushing the cache through the following command:

You can then check the statistics in order to make sure that your cache size is now zero, thus cleared. Run the following command in order to view the statistics:

You cache size 0 in the above output shows that the DNS cache has been cleared.

Method 2: Using dns-clean to flush DNS-Cache

Another way to clear the DNS cache is by starting the dns-clean utility. Run the following command in your Terminal to do so:

You have now learned two effective methods to clear your DNS cache. In both the cases, the process is pretty simple and does not require you to restart your Linux system.

Karim Buzdar

About the Author: Karim Buzdar holds a degree in telecommunication engineering and holds several sysadmin certifications. As an IT engineer and technical author, he writes for various web sites. You can reach Karim on LinkedIn

Источник

How To Clear Or Flush DNS Cache In Linux

This brief guide explains all possible ways to clear or flush DNS cache in Linux operating systems. For those wondering, DNS cache (or sometimes called a DNS resolver cache) is a small temporary database maintained by the operating systems. It stores the information about all visited websites and other Internet domains. In other words, the DNS cache contains recent DNS lookups. When you visit the same website multiple times, the OS retrieves the DNS records of that website from the local DNS cache database instead of the actual public DNS server. Hence DNS caching improves the website loading time and reduces the origin DNS server’s bandwidth/CPU consumption.

Why should you clear or flush DNS cache?

There could be many reasons to clear the local DNS cache. For instance, you might have customized your website or changed the DNS settings for your domain or you are facing some Internet connectivity issues. In such cases, if you attempt to visit the site, your OS will likely to get the cached version of the site from the local DNS cache. So clearing the local DNS cache will delete all entries from the local DNS cache database and force your system to repopulate the DNS cache with new entries from the actual DNS server and display the fresh copy of the website.

Clear Or Flush DNS Cache In Linux

By default, the DNS caching is not installed and/or enabled at the operating system level in Linux. Instead, applications like web browsers maintain their own internal cache. So you can simply clear your browser’s cache or restart them to fix the Internet-connectivity issues, resolve DNS spoofing (e.g. DNS cache poisoning) issues and resolve stale content issues. If your Linux distribution does use any DNS caching services, you need to manually clear them as described below. There are multiple ways to clear DNS cache. It varies depends upon the Linux distribution and DNS caching service you are using. Here I have included instructions to clear the most commonly used DNS caching services in Linux.

1. Clear Systemd-resolve DNS caching service

Systemd-resolve is a systemd service that provides system-level DNS caching service for local applications. It is part of the systemd package which is installed by default. Systemd-resolved service is enabled by default in most modern Linux operating systems such as Fedora and Ubuntu. First, let us check if systemd-resolved service is active or not using command:

If systemd-resolved service is enabled, you will see «active» in the output. If it is not active, it will print «inactive».

Check if systemd-resolved service is active

As you see in the above output, systemd-resolved service is active in my system.

Let us view the statistics of systemd-resolve caching service with command:

Sample output:

As you see, the above output lists the total no of current cache size, hits and missed caches.

To flush the systemd-resolve cache, run:

On successful execution, you will not see any output.

Now, check the systemd-resolve statistics to verify if the local DNS cache is cleared or not.

You will now see current cache size as zero.

Display systemd-resolve statistics

2. Clear Nscd DNS caching service

Nscd, short for name service cache daemon, is a caching daemon that provides a cache for the most common name service requests. It is the preferred caching service for most Redhat-based systems. If your Linux system is using nscd caching service, you can clear or flush the local DNS caching service by simply restarting the nscd service like below:

3. Clear Bind/Named DNS caching service

Berkeley Internet Name Domain (shortly BIND) is the most popular open source DNS server in use today. If you are using BIND for caching DNS queries, use the following commands to clear/flush BIND caching service in Linux:

The latest BID version allows you to clear DNS cache for a specific domain as well. The following command clears the DNS cache for ostechnix.com domain:

You can also clear DNS cache for entire LAN and WAN zones like below:

4. Clear Dnsmasq DNS caching service

Dnsmasq is a lightweight DHCP and caching DNS server with support for PXE and TFTP server. It is suitable for resource constrained routers and firewalls to manage small networks.

If you are using dnsmasq as caching service, you can flush the local DNS caching service like below:

Another way to c lear local DNS cache in Ubuntu and other Ubuntu variants such as Linux Mint is to run the following command:

Источник

How to Clear/Flush the DNS Cache on Linux

You may need to flush or clear the local DNS cache on your Linux system for various reasons.

This could be one of the below reasons.

• Sometimes you may have difficulty reaching certain websites.
• When troubleshooting network related issues.
• After DNS resolvers change.

When you run flush DNS cache, this will destroy the DNS entries in the cache and perform a subsequent query to resolve the domain based on the newly configured DNS settings.

What is DNS cache and what it Does?

The DNS cache is a temporary database maintained by the computer’s operating system.

It stores information about previous DNS lookups (like information on recently visited websites and other web domains).

This will quickly resolve DNS queries when you visit the cached website by getting details from the local DNS database instead of the actual DNS server.

If you want to know DNS information about a website, use one of the commands below.

What is nscd DNS Cache

nscd stands for name service cache daemon, nscd is a daemon that provides a cache for the most common name service requests. The default configuration file located at /etc/nscd.conf .

What is dnsmasq DNS Cache

Dnsmasq is a lightweight, small footprint, easy to configure, DNS forwarder and DHCP server. It is designed to provide DNS and optionally, DHCP, to a small network & suitable for resource constrained routers and firewalls. It can serve the names of local machines which are not in the global DNS. It is designed for personal computer use and small size networks, not for big networks.

What is BIND Server DNS Cache

BIND stands for “Berkeley Internet Name Domain”. The most widely used Name Server Software, BIND is open source software that implements the Domain Name System (DNS) protocols for the Internet. BIND is by far the most widely used DNS software on the Internet, providing a robust and stable platform.

How to Clear/Flush the DNS Cache on Linux

By default, DNS caching is not installed or enabled at the OS level, but if you have installed any of the caching services listed below, use the appropriate commands to flush them.

Below is a list of the major DNS cache services used in the Linux operating system.

• systemd Resolved Service
• nscd DNS Cache
• dnsmasq DNS Cache
• BIND server DNS Cache

1) How to Flush DNS Cache on Linux Using the systemd Resolve Service

Most modern Linux operating systems use systemd, so use the command below to flush the DNS cache.

Run the below command to check if the DNS cache service is active on your system.

You can check the DNS statistics using the below command.

If it’s active and the service is running, use the below command to flush it.

2) How to Clear BIND Server DNS Cache on Linux

The BIND DNS server is used on most servers where the Web Hosting Control Panel is installed. We have seen this on servers where cPanel and CentOS Web Panel are installed.

Run the below command to flush the BIND server DNS cache on Systemd-based Linux systems.

Run the following command to clear the BIND server DNS cache on SysVinit-based Linux systems.

Also, you can use the following commands for the BIND service.

To clear the BIND DNS cache, use the below command.

To clear DNS cache for a particular domain, use the below command.

To clear DNS cache for LAN, use the below command.

To clear DNS cache for WAN, use the below command.

3) How to Flush nscd server DNS Cache on Linux

Some Linux distributions use the nscd DNS server. If so, flush it using the below commands.

Run the below command to flush the nscd server DNS cache on Systemd-based Linux systems.

Run the following command to clear the nscd server DNS cache on SysVinit-based Linux systems.

4) How to Clear the dnsmasq Server DNS Cache on Linux

Some distribution may use the dnsmasq DNS server. If so, use the below commands to flush it.

Run the below command to flush the dnsmasq server DNS cache on Systemd-based Linux systems.

Run the following command to clear the dnsmasq server DNS cache on SysVinit-based Linux systems.

5) How to Clear the DNS Cache on Windows

Use the below command to Flush the dns cache on windows systems.

Conclusion

You have learned how to clear or flush DNS cache on Windows and Linux operating systems.

Источник