How to change hostname in Ubuntu. There are three options: temporary until the first restart and permanent by changing the hostname file or using command hostnamectl

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How to open port for a specific IP address on CentOS 7. Using the firewall-cmd command with add-rich-rule parameter.

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How to build a LAMP stack (Linux, Apache, MySQL, PHP) on CentOS 7. The article includes the install + the firewall settings for public access.

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If you are using a dedicated server with a few GB of RAM then you will not have this problem. But if you are running cloud computing with small virtual server like vultr.com then you may end up in this problem: the mysql/mariadb server will run out of memory.

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SSH has two protocols that can be used, protocol 1 and protocol 2. More about SSH you can found on Wikipedia.

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By default, ssh listens for incoming connections on port 22. So if a hacker wants to attack your machine he will most likely scan port 22 first. Just to make an idea how important is this (from my point of view of course), before changing the default ssh port for my server I got every day 1000+ login tries for my root user. An effective (but minimal) method to protect your machine is to run ssh on non-standard port. Any unused port will work but one above 1024 is preferable.

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