Category: Linux & System Administration

Ubuntu 24 EC2: When EC2 Instance Connect Breaks SSH Key Logins (and How to Fix It)

November 19, 2025

Running Ubuntu 24 on EC2 and suddenly getting Permission denied (publickey) even though your SSH keys are correct? On some images, EC2 Instance Connect is wired into sshd by default and can block key-based logins. This article shows how to confirm EC2 Instance Connect is the culprit and fix the problem by uninstalling it so your servers behave like a normal OpenSSH host again.

“Is 700 world-writable?” — a human’s guide to Linux file permissions

November 16, 2025

Linux file permissions are easy to learn and strangely hard to remember. If you keep forgetting whether 700 is world-writable or what rwxr–r-x means, this guide walks through the 4–2–1 trick, real-world examples, and a few bad jokes to make chmod a little more human.

NTP — A Practical Introduction for Engineers

November 8, 2025

NTP keeps distributed systems in step with reality. This practical introduction explains what NTP is, how its algorithms work, the history from early ARPANET experiments to NTPv4 and NTS, and why accurate time underpins security, logging, replication, and operations—plus how NTP compares with PTP in modern environments.

Is Your Server’s Clock Right?

November 6, 2025

Keep your servers within milliseconds of reality. This hands-on guide shows how to verify system time and timezone, confirm NTP health (chrony, systemd-timesyncd, ntpd), safely correct drift, and harden your setup with best practices. Copy-paste commands included for popular Linux distros.

Daylight Saving Time, Explained

November 5, 2025

Why we change the clocks, who actually does it, where it came from—and how a simple one-hour shift can still trip up cron jobs, logs, calendars, and distributed systems. Practical guidance for engineers included.