How to Access Linux Server Without Password Using SSH

By default, if we want to access the Linux server using ssh then we have to enter the username and password of the server. But it is very inconvenient for a sysadmin if always write a password when want to access the Linux server using ssh. So, this article will explain how to access Linux server using ssh without using a password. I use CentOS 7 and should this article be applicable to OS other than CentOS.
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How to Display Email Subject in Sendmail Log on CentOS 7

Sendmail is a default mail server in some Linux distro like CentOS that is often used by system administrators to email and its use is easy. Unfortunately, by default sendmail log (in /var/log/maillog) do not display the subject, so sysadmins will have difficulties if they have to search for an email based on the title in the log. This article will explain how to display titles in the log in CentOS 7.
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Protect SSH Servers Using DenyHosts on CentOS 7

One way to improve ssh server security is by blocking IPs that often try to access the server. We can do it by install denyhosts application made by Phil Schwartz from python script. The application analyzes the messages in ssh log to determine which IP hosts are trying to access into our system. This article will explain how to install denyHosts on CentOS 7. We first install EPEL repository for CentOS 7 then we do the install by:
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Bash Script to Check Whether a Public IP has been on a SPAM List or Not

Domain Name System Blacklists, also known as DNSBL’s or DNS Blacklists, are spam blocking lists that allow a website administrator to block messages from specific systems that have a history of sending spam. As their name implies, the lists are based on the Internet’s Domain Name System, which converts complicated, numerical IP address such as into domain names such as, making the lists much easier to read, use, and search. If the maintainer of a DNS Blacklist has in the past received spam of any kind from a specific domain name, that server would be “blacklisted” and all messages sent from it would be either flagged or rejected from all sites that use that specific list.
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How to Install Nagios Quickly and Easily

Nagios is an application that monitors systems, networks, and infrastructure and it offers monitoring and alerting services for servers, switches, applications, and services. It alerts users when things go wrong and inform them a second time when the problem has been resolved. Ethan Galstad and a group of developers originally wrote Nagios as NetSaint and its first release in 1999. Nagios is a recursive acronym from Nagios Ain’t Gonna Insist On Sainthood. Sainthood refers to the original name NetSaint, which changed in response to a legal challenge by owners of a similar trademark. Agios (or hagios) also transliterates the Greek word άγιος, which means a saint.
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Let’s Ngoprek …

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I create the website as an online note so I will not forget what I have learned or I have ever oprek. Oprek or Ngoprek is a term in Indonesia which means modify something that usually associated with the computer world.