DNS

sqlplus, tnsping or lsnrctl Hangs

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sqlplus, tnsping or lsnrctl Hangs I can’t cover all situations in this post, but I have some cases that can share with you. Those hanging all point to one problem: Domain name resolution. Does the database server use DNS to do name resolution? Sometimes, DNS traps the name resolution in an unknown and indefinite loop […]
DNS

How to Make Your Mail Trusted by Gmail and Yahoo Mail

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Almost all free mail providers like Gmail and Yahoo Mail will filter out spam or spoofed emails by validating the source (SMTP server), if your mail server have not been validated, the delivered mails may be blocked or directly go to receivers’ Trash folder. Let’s see an example of original message from a doubtful source:…Received-SPF: […]
DNS

How to Resolve NameServer Persistency After Every Reboot

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When we want to change DNS permanently in Linux, what will you do? I guess you will modify /etc/resolv.conf. But newer versions of Linux appear different. Let’s see the following demonstration.First of all, we shall view /etc/resolv.conf.[root@localhost ~]# cat /etc/resolv.conf# Generated by NetworkManagersearch example.comnameserver 168.95.1.1There is a name server, and we change it into 8.8.8.8.[root@localhost […]