Linux Security

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Why a service can stay “activating” after a kernel upgrade

When you bump the kernel, systemd does a hard reset of almost everything.
If a unit you depend on never leaves the activating state, the rest of the boot can stall or the service simply never runs.
The usual suspect is a dependency on a kernel‑provided resource that is missing or delayed after the upgrade.

Below is a practical checklist that shows how to diagnose the issue, why it happens, and how to fix it without compromising security or stability.

Why systemd‑resolved matters

On most modern distros the DNS stack is no longer a simple /etc/resolv.conf.
systemd‑resolved runs in the background, pulls DNS servers from every interface, does caching, validates with DNSSEC, and even acts as a local DNS‑over‑TLS (DoT) proxy.
resolvectl (now systemd-resolve in newer releases) is the CLI that lets you look inside this stack and tweak it without hunting through config files.

If you run a home lab, self‑hosted services, or just want a snappier, more reliable lookup, mastering resolvectl can shave milliseconds off each query and give you a clear view of what the resolver is actually doing.

Introduction to Bash History

As a long-time Linux user, I’ve come to rely on the command line to get my work done. The Bash shell is an incredibly powerful tool, and one of its most useful features is its ability to store a history of previously executed commands. This history is stored in the ~/.bash_history file and can be accessed using the history command. However, as our systems see more use, the Bash history can become cluttered with duplicate entries, making it tough to find the commands we need.

Introduction to systemd Restart Policies

I’ve seen this go wrong when a service is misconfigured and ends up consuming all your system resources. Systemd is a core component of most modern Linux distributions, responsible for managing system services. One of its key features is the ability to automatically restart services that fail or exit unexpectedly. However, if not properly configured, this can lead to a “service deluge” where a failing service is repeatedly restarted.

Introduction to Automated Offsite Backups

I’ve seen this go wrong when people don’t prioritize backups - losing important configuration files can be a real headache. Automating offsite backups is a crucial task for any Linux user, whether you’re a sysadmin, self-hoster, or homelab enthusiast. By leveraging rsync and SSH, you can create a reliable and secure backup system. In this article, we’ll explore how to set up automated offsite backups using these tools.

Introduction to Emergency Mode and Rescue Shell

When your Linux system fails to boot, it can be frustrating - especially if you’re not familiar with the troubleshooting process. I’ve seen this go wrong when people don’t know where to start. Luckily, systemd’s Emergency Mode and Rescue Shell are here to help. In this article, we’ll dive into how to use these tools to troubleshoot initramfs issues and get your system up and running again.

Introduction to Log Noise

When working with Linux systems, logs are an essential part of troubleshooting, monitoring, and maintaining the health of your system. However, with the vast amount of data being logged, it can become overwhelming to sift through the noise to find the important information. I’ve seen this go wrong when trying to debug a complex issue, only to get lost in a sea of irrelevant log messages. This is where journalctl comes in, a powerful tool for managing and filtering system logs.

Introduction to systemd Service Restart Failures

When working with Linux systems, especially those using systemd as the init system, service management is crucial for maintaining system stability and functionality. I’ve seen this go wrong when a service fails to restart properly, often due to dependency ordering issues or retry policy misconfigurations. Understanding how to troubleshoot and resolve these issues is essential for ensuring system reliability and uptime.

Understanding systemd Service Dependencies

Systemd services can have complex dependencies, defined in their service files (typically located in /etc/systemd/system/ or /usr/lib/systemd/system/). These dependencies are crucial for ensuring that services start in the correct order. For example, a web server might depend on the network service to be started before it can operate. Misconfigured dependencies can lead to services failing to start or restart. The real trick is to understand the startup sequence and identify potential bottlenecks.

Introduction to SSH Keys with Multiple Accounts

I’ve seen this go wrong when people try to manage multiple services or projects on a single remote server - they end up with a mess of passwords and login issues. Using SSH keys with multiple accounts is a much better approach. It allows for secure, passwordless login to different user accounts on the same server, which is particularly useful for sysadmins, developers, and self-hosters.