DNS cache flush command on Redhat Linux without systemd-resolved.service

 DNS flush required when you changed the certain domain name IP address's or Domain names. DNS cache will keep the old record so we may need to flush DNS cache to retrieve new IP or Domain names.

resolve.conf usually have the DNS server details 

so DNS flus command also something related to resolve

[root@centos ~]# systemd-resolve --flush-caches

Failed to flush caches: Unit dbus-org.freedesktop.resolve1.service not found.

[root@centos ~]#

//the DNS flush command is not working here, propobly need to check with the resolved services

[root@centos ~]# systemctl status systemd-resolved.service

● systemd-resolved.service - Network Name Resolution

   Loaded: loaded (/usr/lib/systemd/system/systemd-resolved.service; disabled; >

   Active: inactive (dead)

     Docs: man:systemd-resolved.service(8)

           https://www.freedesktop.org/wiki/Software/systemd/resolved

           https://www.freedesktop.org/wiki/Software/systemd/writing-network-co>

           https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-c>

lines 1-7/7 (END)

//resolved.service seems to be inactive, this service must be active in order to flush DNS.

[root@centos ~]# systemctl restart systemd-resolved.service

[root@centos ~]# systemctl status systemd-resolved.service

● systemd-resolved.service - Network Name Resolution

   Loaded: loaded (/usr/lib/systemd/system/systemd-resolved.service; disabled; vendor preset: disabled)

   Active: active (running) since Thu 2021-09-23 05:59:11 PDT; 2s ago

     Docs: man:systemd-resolved.service(8)

           https://www.freedesktop.org/wiki/Software/systemd/resolved

           https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers

           https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients

 Main PID: 35599 (systemd-resolve)

   Status: "Processing requests..."

    Tasks: 1 (limit: 11231)

   Memory: 1.6M

   CGroup: /system.slice/systemd-resolved.service

           └─35599 /usr/lib/systemd/systemd-resolved

//now check the flush command

[root@centos ~]# systemd-resolve --statistics

DNSSEC supported by current servers: yes

Transactions

Current Transactions: 0

  Total Transactions: 2

Cache

  Current Cache Size: 0

          Cache Hits: 0

        Cache Misses: 0

DNSSEC Verdicts

              Secure: 0

            Insecure: 0

               Bogus: 0

       Indeterminate: 0

[root@centos ~]#

[root@centos ~]# systemd-resolve --flush-caches

[root@centos ~]# systemd-resolve --statistics

DNSSEC supported by current servers: yes

Transactions

Current Transactions: 0

  Total Transactions: 2

Cache

  Current Cache Size: 0

          Cache Hits: 0

        Cache Misses: 0

DNSSEC Verdicts

              Secure: 0

            Insecure: 0

               Bogus: 0

       Indeterminate: 0

//now the DNS flush has been done.