Archive for January, 2025

Enable automatic updates on CentOS 8 , CentOS 9 Stream Linux with dnf-automatic and Cockpit Web GUI package management tool

Wednesday, January 15th, 2025

centos-8-and-centos-9-linux-enable-automatic-rpm-yum-updates-with-dnf-automatic-logo

Security for any OS is critical nowadays, thus as a CentOS legacy system admin at work or using CentOS Stream releases 8 and 9 that are to be around for the coming years

CentOS 8 and CentOS 9 Stream Lifecycle


CentOS Stream follows the same lifecycle as Red Hat Enterprise Linux. From version 8 onward this means every version is supported for 10 years, split into 5 years of Full Support and 5 years of maintenance support. Users also have the option to purchase an additional 3 years of Extended Life Cycle Support (ELS) as an add-on.

Version    General Availability    Full Support Ends    Maintenance Support Ends    Extended Life Cycle Support (ELS) Ends
8    May 7, 2019    May 31, 2024    May 31, 2029    May 31, 2032
9    May 18, 2022    May 31, 2027    May 31, 2032    May 31, 2035


In this article, you are going to learn how to enable automatic software updates on CentOS 8 and CentOS 9 ( Stream ) Linux OS-es. I'll show how to set up your system to download and apply  security and other updates without user intervention.

It is really useful to use the CentOS automatic updates OS capability, turning on updates and instead typing all the time yum update && yum upgrade (and wasting time to observe the process) as it takes usually some 5 to 10 minutes to make the OS automatically install updates in the background and notify you once all is done so you can periodically check what the dnf-automatic automatic update tool has done that in most cases of success would save you at least few minutes per host. Automatic updates is critical especially if you have to maintain an infrastructure of CentOS virtual servers at version 8 or 9.

Those who use heavily used CentOS might have already enabled and used dnf-automatic, but I guess just like me until recently, most people using CentOS 8 don’t know how to enable and apply CentOS Linux updates automatically and those article might be helpful.
 

1. Enable Automatic CentOS 8 / 9 Updates Using DNF Automatic RPM Package


Install the DNF-automatic RPM package, it will provide a DNF component that enables start automatically the update process. 
To install it on both CentOS 8 / 9.

[root@centos ~]# yum install dnf-automatic
CentOS Stream 9 – BaseOS                                                                                                                                   78 kB/s |  14 kB     00:00
CentOS Stream 9 – AppStream                                                                                                                                28 kB/s |  15 kB     00:00
CentOS Stream 9 – Extras packages                                                                                                                          81 kB/s |  18 kB     00:00
Dependencies resolved.
======================================================
 Package                                         Architecture                             Version                                          Repository                                Size
======================================================
Installing:
 dnf-automatic                                   noarch                                   4.14.0-23.el9                                    baseos                                    33 k
Upgrading:
 dnf                                             noarch                                   4.14.0-23.el9                                    baseos                                   478 k
 dnf-data                                        noarch                                   4.14.0-23.el9                                    baseos                                    37 k
 python3-dnf                                     noarch                                   4.14.0-23.el9                                    baseos                                   461 k
 yum                                             noarch                                   4.14.0-23.el9                                    baseos                                    88 k

Transaction Summary
=======================================================
Install  1 Package
Upgrade  4 Packages

Total download size: 1.1 M
Is this ok [y/N]: y
Downloading Packages:
(1/5): dnf-data-4.14.0-23.el9.noarch.rpm                                                                                                                  556 kB/s |  37 kB     00:00
(2/5): dnf-automatic-4.14.0-23.el9.noarch.rpm                                                                                                             406 kB/s |  33 kB     00:00
(3/5): yum-4.14.0-23.el9.noarch.rpm                                                                                                                       1.4 MB/s |  88 kB     00:00
(4/5): python3-dnf-4.14.0-23.el9.noarch.rpm                                                                                                               4.9 MB/s | 461 kB     00:00
(5/5): dnf-4.14.0-23.el9.noarch.rpm                                                                                                                       2.6 MB/s | 478 kB     00:00
——————————————————————————————————
Total                                                                                                                                                     1.1 MB/s | 1.1 MB     00:00
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
  Preparing        :                                                                                                                                                                  1/1
  Upgrading        : dnf-data-4.14.0-23.el9.noarch                                                                                                                                    1/9
  Upgrading        : python3-dnf-4.14.0-23.el9.noarch                                                                                                                                 2/9
  Upgrading        : dnf-4.14.0-23.el9.noarch                                                                                                                                         3/9
  Running scriptlet: dnf-4.14.0-23.el9.noarch                                                                                                                                         3/9
  Installing       : dnf-automatic-4.14.0-23.el9.noarch                                                                                                                               4/9
  Running scriptlet: dnf-automatic-4.14.0-23.el9.noarch                                                                                                                               4/9
  Upgrading        : yum-4.14.0-23.el9.noarch                                                                                                                                         5/9
  Cleanup          : yum-4.14.0-9.el9.noarch                                                                                                                                          6/9
  Running scriptlet: dnf-4.14.0-9.el9.noarch                                                                                                                                          7/9
  Cleanup          : dnf-4.14.0-9.el9.noarch                                                                                                                                          7/9
  Running scriptlet: dnf-4.14.0-9.el9.noarch                                                                                                                                          7/9
  Cleanup          : python3-dnf-4.14.0-9.el9.noarch                                                                                                                                  8/9
  Cleanup          : dnf-data-4.14.0-9.el9.noarch                                                                                                                                     9/9
  Running scriptlet: dnf-data-4.14.0-9.el9.noarch                                                                                                                                     9/9
  Verifying        : dnf-automatic-4.14.0-23.el9.noarch                                                                                                                               1/9
  Verifying        : dnf-4.14.0-23.el9.noarch                                                                                                                                         2/9
  Verifying        : dnf-4.14.0-9.el9.noarch                                                                                                                                          3/9
  Verifying        : dnf-data-4.14.0-23.el9.noarch                                                                                                                                    4/9
  Verifying        : dnf-data-4.14.0-9.el9.noarch                                                                                                                                     5/9
  Verifying        : python3-dnf-4.14.0-23.el9.noarch                                                                                                                                 6/9
  Verifying        : python3-dnf-4.14.0-9.el9.noarch                                                                                                                                  7/9
  Verifying        : yum-4.14.0-23.el9.noarch                                                                                                                                         8/9
  Verifying        : yum-4.14.0-9.el9.noarch                                                                                                                                          9/9

Upgraded:
  dnf-4.14.0-23.el9.noarch                   dnf-data-4.14.0-23.el9.noarch                   python3-dnf-4.14.0-23.el9.noarch                   yum-4.14.0-23.el9.noarch
Installed:
  dnf-automatic-4.14.0-23.el9.noarch

Complete!
[root@centos ~]#

Here is info on what dnf-automatic package will do: 

[root@centos ~]# rpm -qi dnf-automatic
Name        : dnf-automatic
Version     : 4.14.0
Release     : 23.el9
Architecture: noarch
Install Date: Wed 15 Jan 2025 08:00:47 AM -03
Group       : Unspecified
Size        : 57937
License     : GPLv2+
Signature   : RSA/SHA256, Thu 02 Jan 2025 01:19:43 PM -03, Key ID 05b555b38483c65d
Source RPM  : dnf-4.14.0-23.el9.src.rpm
Build Date  : Thu 12 Dec 2024 07:30:24 AM -03
Build Host  : s390-08.stream.rdu2.redhat.com
Packager    : builder@centos.org
Vendor      : CentOS
URL         : https://github.com/rpm-software-management/dnf
Summary     : Package manager – automated upgrades
Description :
Systemd units that can periodically download package upgrades and apply them.


Next up is configuring the dnf-automatic updates. The configuration file is located at /etc/dnf/automatic.conf. Once you have opened the file, you can to set the required values to fit your software requirements.
The values you might want to modify are as so:

 

[root@centos ~]# grep -v \# /etc/dnf/automatic.conf|sed '/^$/d'
[commands]
upgrade_type = default
random_sleep = 0
network_online_timeout = 60
download_updates = yes
apply_updates = no
reboot = never
reboot_command = "shutdown -r +5 'Rebooting after applying package updates'"
[emitters]
emit_via = stdio
[email]
email_from = root@example.com
email_to = root
email_host = localhost
[command]
[command_email]
email_from = root@example.com
email_to = root
[base]
debuglevel = 1
[root@centos ~]#

 

The most important things you need to tune in automatic.conf are:

[root@centos ~]# vim /etc/dnf/automatic.conf

apply_updates = no


should be changed to yes 

apply_updates = yes

for automatic updates to start by dnf-automatic service

It is nice to set the email server to use configuration values, as well as email from, email to and the way for
email to be set emit_via = stdio is default (check out the other options if to be used inside the commented lines)

Finally, you can now run dnf-automatic, execute the following command to schedule DNF automatic updates for your CentOS 8 machine.

[root@centos ~]# systemctl enable –now dnf-automatic.timer


The command above enables and starts the system timer. To check the status of the dnf-automatic service, run the following.

[root@centos ~]#  systemctl list-timers *dnf-*
NEXT                        LEFT       LAST                        PASSED      UNIT                ACTIVATES
Wed 2025-01-15 09:31:52 -03 13min left –                           –           dnf-makecache.timer dnf-makecache.service
Thu 2025-01-16 06:21:20 -03 21h left   Wed 2025-01-15 08:09:20 -03 1h 8min ago dnf-automatic.timer dnf-automatic.service

2 timers listed.
Pass –all to see loaded but inactive timers, too.

[root@centos ~]#

 

Enable and Manage Automatic updates with Cockpit GUI web interface


Sooner or later even hard core sysadmins has to enter the 21 century and start using a Web interfaces for server or Desktop Linux management to offload your head for more important stuff.
Cockpit is a great tool to help you automatically manage and update your servers with no need to use the Linux console most of the time.

Cockpit is a very powerful tool you can use to manage remotely updates through a web interface, it is very handy tool for system admins as it gives you overview over updates and supports automatic updates and set RPM package management tasks through web-based console. 
Cockpit allows updates over multiple servers and it makes it a kind of server orchestration tool that allows yo to update many same versioned operating system software.


If you haven't it already pre-installed in CentOS 8 / 9 depending on the type ofinstall you have done, you might need to install Cockpit.

To install cockpit

[root@centos ~]# yum install cockpit -y

To make the web service accessible in a browser you'll have to start it with cmds:

[root@centos ~]# systemctl start cockpit
[root@centos ~]# systemctl status cockpit

To access cockpit you'll either have to access it on https://localhost:9090 in case you need to access it locally via https://SERVER_IP:9090/.
Note that of course you will have to have firewalld enabling traffic to SERVER_IP PORT 9090.

 

centos-steam-cockpit-web-gui-autoupdate-tool-linux-screenshot1

By default cockpit will run with self signed certificate, if you need you can set up a certbot certificate or regenerate the self signed one for better managed security risk. For a first time if you haven't changed the certificate simply use the browser exclusion menu and login to Cockpit.

Once logged in you can check the available updates.

 

centos-steam-cockpit-web-gui-autoupdate-tool-linux-screenshot0

By default you will have to login with non-root account, preferably that should be an account who is authorized to become root via sudo.
To elevate to administrative privileges while in cockpit clock on 'Administrative access' and grant cockpit your superuser privileges.

centos-steam-cockpit-web-gui-autoupdate-tool-linux-screenshot2

Once authorized you can run the upgrade and enojy a coffee or beer in the mean time 🙂

centos-steam-cockpit-web-gui-autoupdate-tool-linux-screenshot-update-ongoing

Among the useful cockpit options, is also the Terminal through which you can run commands like over a normal Web SSH service.

The 'Logs' section is also very useful as it shows you clearly synthesized information on failed services and modules, since last OS system boot.

 

https://pc-freak.net/images/centos-steam-cockpit-web-gui-autoupdate-tool-linux-screenshot3

To add and manage updates for multiple hosts use the 'Add new host' menu that is a expansion of the main machine on which cockpit runs.


centos-steam-cockpit-web-gui-autoupdate-tool-linux-automatic-updates-settings

In the next window, turn automatic updates ON. You can now select the type of updates you want (Apply All Updates or Apply Security Updates), the day and time you want the updates applied, and the server rebooted.

CentOS 9's cockpit even have support for the innovative Kernel live patching, so the machine kernel can be updated even Live and you can save the reboot after complete patching of OS including the kernel.

centos-steam-cockpit-web-gui-autoupdate-tool-linux-kernel-live-patching-menu

Note that you cannot set up automatic updates without rebooting the system. Therefore, make sure your server can be rebooted at the time you’ve selected for the updates.

Sum it up


In this post, we learned have learned how to set up automatic updates for your CentOS 8 / 9 Linux. There are two main stream ways you can do it.
1. By using DNF automatic updates tool.
By enabling DNF automatic updates on CentOS 8 Linux the machine updated is faster, seemless and frequent as compared to manual updates.

This protects the OS more about crackers cyber-attacks. Secondly for the more lazy admins or for better structuring of updates (if it has to be executed on multiple hosts), the Cockpit web console is available.

With Cockpit, it’s much easy to enable automatic updates as the GUI is self-explanatory graphical user interface (GUI) as opposed to the DNF automatic updates, which would waste you more time on CLI ( shell ).
 

Enable Debian Linux automatic updates to keep latest OS Patches / Security Up to Date

Monday, January 13th, 2025

Enable Debian Linux automatic updates to keep latest OS Patches / Security Up to Date

Debian: Entenda a Importância Para o Mundo GNU/LINUX

I'm not a big fan of automatism on GNU / Linux as often using automatic updates could totally mess things especially with a complex and a bit chatic OS-es like is Linux nowadays. 
Nevertheless as Security is becoming more and more of a problem especially the browser security, having a scheduled way to apply updates like every normal modern Windows and MAC OS as an option is becoming essential to have a fully manageble Operating system.

As I use Debian GNU / Linux for desktop for my own personal computer and I have already a lot of Debian servers, whose OS minor level and package version maintenance takes up too big chunk of my time (a time I could dedicated to more useful activities). Thus I found it worthy at some cases to trigger Debian's way to keep the OS and security at a present level, the so called Debian "unattended upgrades".

In this article, I'll explain how to install and Enable Automatic (" Unattended " ) Updates on Debian, with the hope that other Debian users might start benefiting from it.
 

Pros of  enabling automatic updates, are:

  • Debian OS Stay secure without constant monitoring.
  • You Save much time by letting your system handle updates.
  • Presumably Enjoying more peace of mind, knowing your system is more protected.

Cons of enabling automatic updates:

  • Some exotic and bad maintained packages (might break after the update)
  • Customizations made on the OS /etc/sysctl.conf or any other very custom server configs might disappear or not work after the update
  • At worst scenario (a very rare but possible case) OS might fail to boot after update 🙂

Regular security updates patch vulnerabilities that could otherwise be exploited by attackers, which is especially important for servers and systems exposed to the internet, where threats evolve constantly.

1. Update Debian System to latest

Before applying automatic updates making any changes, run apt to update package lists and upgrade any outdated packages,to have automatic updates for a smooth configuration process.

# apt update && apt upgrade -y

2. Install the Unattended-Upgrades deb Package 

# apt install unattended-upgrades -y

Reading package lists… Done
Building dependency tree… Done
Reading state information… Done
The following additional packages will be installed:
  distro-info-data gir1.2-glib-2.0 iso-codes libgirepository-1.0-1 lsb-release python-apt-common python3-apt python3-dbus python3-distro-info python3-gi
Suggested packages:
  isoquery python-apt-doc python-dbus-doc needrestart powermgmt-base
The following NEW packages will be installed:
  distro-info-data gir1.2-glib-2.0 iso-codes libgirepository-1.0-1 lsb-release python-apt-common python3-apt python3-dbus python3-distro-info python3-gi unattended-upgrades
0 upgraded, 11 newly installed, 0 to remove and 0 not upgraded.
Need to get 3,786 kB of archives.
After this operation, 24.4 MB of additional disk space will be used.
Do you want to continue? [Y/n]

 

 

# apt install apt-listchanges
Reading package lists… Done
Building dependency tree… Done
Reading state information… Done
The following package was automatically installed and is no longer required:
  linux-image-5.10.0-30-amd64
Use 'apt autoremove' to remove it.
The following additional packages will be installed:
  python3-debconf
The following NEW packages will be installed:
  apt-listchanges python3-debconf
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 137 kB of archives.
After this operation, 452 kB of additional disk space will be used.
Do you want to continue? [Y/n]
Get:1 http://deb.debian.org/debian bookworm/main amd64 python3-debconf all 1.5.82 [3,980 B]
Get:2 http://deb.debian.org/debian bookworm/main amd64 apt-listchanges all 3.24 [133 kB]
Fetched 137 kB in 0s (292 kB/s)
Preconfiguring packages …
Deferring configuration of apt-listchanges until /usr/bin/python3
and python's debconf module are available
Selecting previously unselected package python3-debconf.
(Reading database … 84582 files and directories currently installed.)
Preparing to unpack …/python3-debconf_1.5.82_all.deb …
Unpacking python3-debconf (1.5.82) …
Selecting previously unselected package apt-listchanges.
Preparing to unpack …/apt-listchanges_3.24_all.deb …
Unpacking apt-listchanges (3.24) …
Setting up python3-debconf (1.5.82) …
Setting up apt-listchanges (3.24) …

Creating config file /etc/apt/listchanges.conf with new version

 

Example config for apt-listchanges would be like:

# vim /etc/apt/listchanges.conf
[apt]
frontend=pager
email_address=root
confirm=0
save_seen=/var/lib/apt/listchanges.db
which=both

3. Enable Automatic unattended upgrades

Once installed, enable automatic updates with the following command, which will prompt asking if you want to enable automatic updates. Select Yes and press Enter, which will confirm that the unattended-upgrades service is active and ready to manage updates for you.

# dpkg-reconfigure unattended-upgrades

Configure-Unattended-Upgrades-on-Debian_Linux-dpkg-reconfigure-screenshot

Or non-interactively by running command:

# echo unattended-upgrades unattended-upgrades/enable_auto_updates boolean true | debconf-set-selections
dpkg-reconfigure -f noninteractive unattended-upgrades


4. Set the Schedule for Automatic Updates on Debian

By default, unattended-upgrades runs daily, to verify or modify the schedule, check the systemd timer:

# sudo systemctl status apt-daily.timer
# sudo systemctl status apt-daily-upgrade.timer
# systemctl edit apt-daily-upgrade.timer

Current apt-daily.timer config as of Debian 12 (bookworm) is as follows

root@haproxy2:/etc/apt/apt.conf.d# cat  /lib/systemd/system/apt-daily.timer
[Unit]
Description=Daily apt download activities

[Timer]
OnCalendar=*-*-* 6,18:00
RandomizedDelaySec=12h
Persistent=true

[Install]
WantedBy=timers.target
root@haproxy2:/etc/apt/apt.conf.d#


 

# systemctl edit apt-daily-upgrade.timer

[Timer]
OnCalendar=
OnCalendar=03:00
RandomizedDelaySec=0

 

At Line  num 2 above is needed to reset (empty) the default value shown below in line  num 5.
Line 4 is needed to prevent any random delays coming from the defaults.


Now both timers should be active, if not, activate them with:

# systemctl enable –now apt-daily.timer
# systemctl enable –now apt-daily-upgrade.timer


These timers ensure that updates are checked and applied regularly, without manual intervention.

5.Test one time Automatic Updates on Debian works

To ensure everything is working, simulate an unattended upgrade with a dry run:

# unattended-upgrade –dry-run

 

You can monitor automatic updates by checking the logs.

# less /var/log/unattended-upgrades/unattended-upgrades.log

Log shows details of installed updates and any issues that occurred. Reviewing logs periodically can help you ensure that updates are being applied correctly and troubleshoot any problems.

6. Advanced Configuration Options

If you’re a power user or managing multiple systems, you might want to explore these additional settings in the configuration file:

# vim /etc/apt/apt.conf.d/50unattended-upgrades


Configure unattended-upgrades to send you an email whenever updates are installed.

Unattended-Upgrade::Mail "your-email-address@email-address.com";


Enable automatic reboots after kernel updates
by adding the line:

Unattended-Upgrade::Automatic-Reboot "true";

To schedule reboots after package upgrade is applied  at a specific time:

Unattended-Upgrade::Automatic-Reboot-Time "02:00";

Specify packages you don’t want to be updated by editing the Unattended-Upgrade::Package-Blacklist section in the configuration file.

 

Here is alternative way to configure the unattended upgrade, by using apt configuration options:

# vim /etc/apt/apt.conf.d/02periodic

// Control parameters for cron jobs by /etc/cron.daily/apt-compat //


// Enable the update/upgrade script (0=disable)
APT::Periodic::Enable "1";


// Do "apt-get update" automatically every n-days (0=disable)
APT::Periodic::Update-Package-Lists "1";


// Do "apt-get upgrade –download-only" every n-days (0=disable)
APT::Periodic::Download-Upgradeable-Packages "1";


// Run the "unattended-upgrade" security upgrade script
// every n-days (0=disabled)
// Requires the package "unattended-upgrades" and will write
// a log in /var/log/unattended-upgrades
APT::Periodic::Unattended-Upgrade "1";


// Do "apt-get autoclean" every n-days (0=disable)
APT::Periodic::AutocleanInterval "21";


// Send report mail to root
//     0:  no report             (or null string)
//     1:  progress report       (actually any string)
//     2:  + command outputs     (remove -qq, remove 2>/dev/null, add -d)
//     3:  + trace on
APT::Periodic::Verbose "2";

If you have to simultaneously update multiple machines and you're on a limited connection line, configure download limits if you’re on a metered connection by setting options in /etc/apt/apt.conf.d/20auto-upgrades.

7. Stop Automatic Unattended Upgrade

Under some circumstances if it happens the unattended upgrades are no longer required and you want to revert back to manual package updates, to disable the updates you have to disable the unattended-upgrades service

# systemctl stop unattended-upgrades


8.  Stop an ongoing apt deb package set of updates applied on Debian server

Perhaps not often, but it might be you have run an automated upgrade and this has broke a server system or a service and for that reason you would like to stop the upcoming upgrade (some of whose might have started on other servers) immediately, to do so, the easiest way (not always safe thogh) is to kill the unattended-upgrades daemon.
 

# pkill –signal SIGKILL unattended-upgrades


Note that this a very brutal way to kill it and that might lead to some broken package update, that you might have to later fix manually.

If you have the unattended-upgrade process running on the OS in the process list backgrounded and you want to stop the being on the fly upgrade on the system more safely for the system, you can stop and cancel the ongoing apt upgrade  it by running the ncurses prompt interface, through dpkg-reconfigure

# dpkg-reconfigure unattended-upgrades


Then just select No, press Enter. In my case, this has promptly stopped the ongoing unattended upgrade that seemed blocked (at least as promptly as the hardware seemed to allow 🙂 ).

If you want to disable it for future, so it doesn't automatically gets enabled on next manual update, by some update script disable service as well.
 

# systemctl disable unattended-upgrades

 

Close up

That’s all ! Now, your Debian system will automatically handle security updates, keeping your system secure without you having to do a thing.
The same guide should be good for most Deb based distributions such as Ubuntu / Mint and there rest of other Debian derivative OS-es.
You’ve now set up a reliable way to ensure your system stays protected from vulnerabilities, but anyways it is a good practice to always login and check what the update has done to the system, otherwise expect the unexpected. 

Flush DNS on Mac OS X ,Windows and Linux from command line

Wednesday, January 8th, 2025

MAC OSX DNS Configuration | DNSFLEX

 

MAC OS X flush DNS cache


Open macOS /Mac OS X terminal application and type the following command under OS X version 10.5 and above:

# dscacheutil -flushcache

Mac OS X Tiger (v10.4) user, enter:

# lookupd -flushcache

macOS 11 Big Sur or 12 Monterey user, try:

# sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

 

macOS 10.11 El Capitan, 10.12 Sierra, 10.13 High Sierra, 10.14 Mojave, or 10.15 Catalina user try:

# sudo killall -HUP mDNSResponder

 

On Mac OS X version 10.6 and onwards to dump DNS cached records
 

$ dscacheutil -cachedump -entries

Display your DNS cached records on Windows
 
Implement Windows Server DNS - Training | Microsoft Learn

  DNS cached records are stored to offload the DNS from querying it all the time in order to resolve the questionable site domain IP.

To view most recent cached DNS records on Windows use cmd:
 

c:\Windows\> ipconfig /displaydns

 

Windows IP Configuration

    array805.prod.do.dsp.mp.microsoft.com
    —————————————-
    Record Name . . . . . : array805.prod.do.dsp.mp.microsoft.com
    Record Type . . . . . : 1
    Time To Live  . . . . : 1894
    Data Length . . . . . : 4
    Section . . . . . . . : Answer
    A (Host) Record . . . : 52.143.124.236


    telemetry-incoming.r53-2.services.mozilla.com
    —————————————-
    Record Name . . . . . : telemetry-incoming.r53-2.services.mozilla.com
    Record Type . . . . . : 1
    Time To Live  . . . . : 444
    Data Length . . . . . : 4
    Section . . . . . . . : Answer
    A (Host) Record . . . : 34.120.208.123


    tunnel.googlezip.net
    —————————————-
    Record Name . . . . . : tunnel.googlezip.net
    Record Type . . . . . : 1
    Time To Live  . . . . : 36756
    Data Length . . . . . : 4

Use up/down scroll array to see the cached record you need to view in the DNS cache.
 

Flush DNS Cache on Windows OS

 


Open the terminal (Start > Run > type cmd and press the [Enter] key) and type the following command to flush DNS on Win XP/2000/7/10 etc:

# ipconfig /flushdns

 

How to Flush DNS local cache queries on Linux

How to Flush DNS Cache on Linux | Linux How to Flush DNS Guide

 

If you’re using a Linux distro such as Ubuntu, here’s how to flush the DNS cache:

Open the terminal by pressing Ctrl + Alt + T or searching for “Terminal” in the Activities menu.
Run the following command:
If you are running Ubuntu 20.04 LTS Linux or older Linux distro using systemd-resolve, use: sudo systemd-resolve –flush-caches.
If you are running Ubuntu 22.04 LTS or newer, use: sudo resolvectl flush-caches.
Enter your administrator password when prompted, and the DNS cache will be flushed.

To check the change in the DNS record is real, you can check the DNS cache statistics:

# resolvectl statistics

On older Linux distributions where /etc/resolv.conf nameserver directives are used to set the DNS for the server, to flush the cache
only options is to either flush the server used cache or change the nameserver inside the file.

 

Check the DNS cache records on older Linux distros (requires NSCD daemon)

Assuming the nscd daemon is UP and running (if not you have to install it) to check the cached local DNS records on Linux do

# service nscd status 


Reviewing Your DNS Cache on modern Linux distros

The systemd-resolved daemon reacts to USR1 by writing its cache to the system logs. We can then use the journalctl command to filter out the DNS entries.

We'll use the killall command with USR1 To send the signal to the systemd-resolved daemon. Note that although we're using the killall command, the systemd-resolved daemon continues to run. This isn't a termination signal that we're sending.

$ sudo killall -USR1 systemd-resolved

Now we'll use the journalctl command with the -u (filter by systemd unit) option to extract the log entries that have been generated by systemd-resolved . We'll redirect that output into a text files called "dns.txt."

$ sudo journalctl -u systemd-resolved > dns.txt

Then check the DNS records

$ less dns.txt

 

Then find the cached mappings between domain names and IP addresses in.

How to Flush the dnsmasq Cache on Linux

The dnsmasq application provides a DNS cache and a DHCP server.

dnsmasq is popular among with users who want to run their own DNS server, especially on non-systemd installations.

Flushing the dnsmasq DNS cache is easy. We need to send the SIGHUP signal, which tells the dnsmasq daemon to effectively reinitialize. Doing so clears its DNS cache. To send the signal we use the killall command with the -HUP flag, and the name of the application.

$ sudo killall -HUP dnsmasq