If you search for the usage of the sed/awk command on the Internet, you will get tons of tutorials teaching you how to use them. I have learnt sed/awk for dozen of years but still cannot write a valid sed/awk…

I’m investigating my hacked website under xampp environment. I put my website files in c:\xampp\htdocs\domainhostseotool\, and visit the site as localhost/domainhostseotool. I’m little worried about a possible security risk. Suppose the compromised website has an infected php file which contains…

Yum repositories are like websites that you can download software from. Yum has default repositories to download packages so you do not need to configure repos to use yum to install/upgrade packages on your system. But that is not enough.…

If you set name servers in your domain registrar but have not added the domain in your hosting company, what is the DNS status of your domain? nslookup xxx.com Server:  UnKnown Address:  yy.yy.yy.yy *** UnKnown can’t find xxx.com: Server failed…

According to rfc2822, an email message is:    A message that is conformant with this standard is comprised of characters with values in the range 1 through 127 and interpreted as US-ASCII characters [ASCII].  For brevity, this document sometimes refers…

Even after you set up a SPF record and a DKIM record, your email may also be rejected or delivered to junk box if you did not set up a DMARC DNS record. How to add a DMARC record in…

Cyrus-imap is an error-prone program. To debug it, you need to edit /etc/imap.conf to add “debug:1″ and create a user directory in /var/log/imap/log/admin to log the protocol messages. You need to know the log sequences for successful cases: Sep 14…

openssl s_client -connect domainhostseotool.com:995 user admin@domainhostseotool.com pass yourpassword stat (show total messages and size of the messages) list (show each message on a new line, including message number and the size of the message) retr messagenumber (retrieve the content of…

You may be looking for VPNs that open outgoing port 25. The famous VPN providers won’t tell you on their homepage they have blocked outgoing port 25 for preventing from spamming. You may have to buy one VPN after another…

When I migrated my website from CentOS 6 to CentOS 7, I found the wordpress site stopped working. Only the homepage can be displayed, other internal pages of the website “are not found”. Even the homepage is not displayed properly…