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What is a port number?
If an IP address finds the server, the port finds the right program on it. The common ports, and how to see which ones…
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RAID levels explained: 0, 1, 5, 6 and 10
How each RAID level spreads data across disks, how many failures it survives, how much space you keep, and why RAID is still not…
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What is caching? Browser, page and object caches
Caching keeps a ready-made copy of something so it does not have to be built again. The layers that make websites fast, and when…
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How HTTPS works
What the padlock actually means, what a certificate proves, and what happens in the first fraction of a second of every secure connection.
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What is a CDN?
A content delivery network keeps copies of your site’s files in data centers around the world, so visitors download them from somewhere close.
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What is an IP address? IPv4 and IPv6 explained
The number every device on the internet uses to find every other device, the difference between IPv4 and IPv6, and public versus private addresses.
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What is a reverse proxy?
A server that stands in front of your other servers, takes every request and decides who answers. What it does, when you need one,…
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How to back up a Linux server
Dump the databases, copy the files to another machine every night with rsync and cron, and prove the backup works by restoring it.
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How to turn on automatic security updates
Have the server install security patches by itself every day, on Ubuntu with unattended-upgrades and on RHEL-based systems with dnf-automatic.
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How to set up a firewall on Linux
Block everything except SSH and the web with UFW on Ubuntu or firewalld on RHEL-based systems, without locking yourself out.
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How to get a free SSL certificate with Let’s Encrypt
Issue a trusted HTTPS certificate in one command with Certbot, redirect HTTP to HTTPS, and make sure it renews by itself.
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How to install Nginx on Ubuntu
Install Nginx, serve your first site from its own folder, and learn the three commands you will use every time you change its configuration.
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How to set up SSH keys
Replace passwords with a key pair, log in without typing a password, and then switch password login off for good.
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How to connect to a server with SSH
Open a secure command line on a remote server from Windows, macOS or Linux, and understand the host key prompt you see the first…
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How to migrate a cPanel account to another cPanel server
Three ways to move a whole cPanel account (files, databases, email and DNS zone) to a new server, with annotated WHM screenshots for each.
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How to migrate email to a new host
Copy mailboxes over IMAP, switch the MX records, and pick up the stragglers, without losing a single message.
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How to change hosts without downtime
Run the old and new servers side by side, switch DNS when the new one is proven, and keep the old one answering until…
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Website migration checklist
Everything to check before, during and after moving a website to a new host, so nothing is forgotten and nothing breaks.
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How to move a WordPress site to a new host
Copy the files and database, test on the new server before anyone else sees it, then switch DNS with the old host kept as…
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How to flush your DNS cache
Make your computer forget old DNS answers after a site move or record change. Commands for Windows, macOS, Linux and every major browser.
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How to set up SPF, DKIM and DMARC
Three DNS records that prove your email is really from you, so it reaches inboxes and nobody else can send as your domain.
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What is a nameserver?
Nameservers hold your domain’s DNS records. Changing them moves control of every record to a new provider at once.
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How to point a domain to a server
Connect a domain to your hosting by setting A records, adding www, and checking the change before you rely on it.
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What is DNS propagation, and how long does it take?
Why a DNS change reaches some people in minutes and others in hours, how to check its progress, and how to make the next…