Linux Security

Introduction to Emergency Mode

I’ve seen this go wrong when a Linux system encounters a critical issue during boot - it can be a real headache. But, thankfully, Linux has a built-in safety net called emergency mode. This mode kicks in when there’s a failed filesystem check or an inability to mount a necessary partition, providing a minimal environment for troubleshooting and repair. With the advancements in Linux, understanding how to use emergency mode is crucial for system administrators and users alike.

Introduction to Disk Space Issues

I’ve seen this go wrong when managing Linux systems - the sudden disappearance of disk space. It’s often caused by log files filling up the disk, large files being stored in unexpected locations, or even malware consuming disk space. In this article, I’ll focus on tracking down and preventing logs from filling up your Linux disks.

Understanding Log Files

Log files are essential for Linux system administration, providing valuable information about system events, errors, and security issues. However, if not properly managed, log files can grow rapidly and consume large amounts of disk space. The most common log files that can cause issues are:

Introduction to DNS Leaks

I’ve seen DNS leaks cause issues on even the most secure Linux servers. Ensuring your DNS setup is solid is crucial, and one common problem is a DNS leak, where your system inadvertently reveals your DNS queries to unauthorized parties. In this article, I’ll walk you through troubleshooting DNS leaks using systemd-resolved and resolv.conf on a Linux server.

Understanding systemd-resolved

systemd-resolved is a powerful tool that provides DNS resolution capabilities. It’s designed to be a caching, validating DNS resolver that can also handle DNSSEC validation. To check if systemd-resolved is running on your system, use the following command:

Introduction to Debugging systemd Services

I’ve seen this go wrong when you’re trying to troubleshoot issues with your Linux system - those pesky systemd services can be a real pain. They’re the backbone of your system, managing everything from network connections to system logging. Debugging these services can be a daunting task, especially for those new to Linux administration. Fortunately, systemd provides two powerful tools to help you diagnose and resolve issues: systemd-analyze and journalctl.

Introduction to Split DNS Chaos

I’ve seen this go wrong when working with multiple networks or self-hosted services: split DNS configurations can become a real headache. Luckily, many Linux distributions have started adopting systemd-resolved as the default DNS resolver, which makes managing split DNS scenarios much simpler. In this article, I’ll walk you through how to use systemd-resolved for local hostname resolution and taming that split DNS chaos.

Understanding systemd-resolved

The real trick is understanding how systemd-resolved works. It’s a systemd component that provides DNS resolution and caching, and it can be configured to use multiple DNS servers and handle split DNS scenarios with ease. To check if systemd-resolved is enabled on your system, run the following command:

Introduction to Btrfs Snapshots

I’ve worked with Btrfs for a while now, and one of its most useful features is snapshotting. This allows you to create a read-only copy of a subvolume at a given point in time, which is perfect for backups, testing, and rolling back changes. However, over time, these snapshot copies can accumulate and consume significant disk space. In practice, this can become a real issue if you’re not careful.

Introduction to Troubleshooting Slow DNS Lookups

I’ve seen slow DNS lookups bring Linux systems to a crawl, and with our increasing reliance on online services, efficient DNS resolution is crucial. This article focuses on troubleshooting slow DNS lookups using systemd-resolved and resolvectl, which are integral to many modern Linux distributions.

Understanding systemd-resolved

systemd-resolved is a system service that provides DNS resolution, replacing traditional implementations like glibc’s resolver. It offers improved security, better DNSSEC handling, and efficient management of multiple DNS servers. To check if it’s running on your system, use:

Introduction to systemd-resolved

I’ve worked with Linux systems for years, and one thing that’s become increasingly important is DNS resolution. systemd-resolved is a DNS resolver component of the systemd suite, designed to provide a flexible and secure way to resolve domain names. It was introduced in systemd version 216, released in 2015, and has since become a standard component in many Linux distributions. By default, systemd-resolved uses a split DNS configuration, which can sometimes lead to DNS leaks and unexpected behavior. I’ve seen this go wrong when a system has multiple network interfaces or connections, each with its own DNS resolver configuration.

Introduction to Log Rotation with systemd

I’ve seen log files consume entire disks, bringing systems to a grinding halt. That’s why log rotation is crucial - it ensures your logs don’t get out of control. With systemd, you’ve got a robust mechanism for managing and rotating logs. In this article, I’ll dive into using systemd for log rotation, covering its benefits, configuration, and some practical examples.

Understanding systemd’s Role in Log Rotation

systemd’s journald is a game-changer for log management. It collects and stores log messages from various sources, including systemd services, kernel messages, and other system components. This centralized logging system makes it easier to manage and rotate logs. By leveraging systemd’s capabilities, you can configure log rotation to suit your specific needs, keeping your system stable and secure.

Introduction to systemd-resolved

I’ve been using systemd-resolved for a while now, and I have to say, it’s a big improvement over traditional DNS resolvers. As of 2026, many Linux distributions, including Ubuntu, Debian, and Fedora, have adopted systemd-resolved as the default DNS resolver. While it offers several benefits, including improved security and performance, some users may encounter issues or require customization to suit their specific needs. Don’t bother with trying to disable it, though - it’s usually worth the effort to get it working right.