Page 9 - Linux

Anyone who treats kernel modules as a black box is missing one of the most useful diagnostic tools on Linux. lsmod, modinfo and modprobe show which drivers and subsystems are actually loaded, how dependencies between modules get resolved, and how to load, remove or permanently block a module without ever recompiling the kernel.

A stolen server or a removed disk is an open book without encryption. LUKS encrypts entire block devices transparently for the filesystem on top and can even be unlocked automatically with keyfiles, without sacrificing protection against physical theft.

chroot is one of the oldest isolation tools on Unix and, at the same time, one of the most misunderstood. Anyone building a jail environment to seal off a process from the rest of the filesystem must understand exactly what chroot actually secures and where that protection ends, since many servers have already been compromised through a chroot environment mistakenly believed to be secure.

An environment variable that works fine in the administrator's shell but is simply missing inside the PHP-FPM process of a Magento application is one of the most common puzzles in daily server operations. The reason is almost always scope: environment variables are only inherited by child processes, never backward and never across independent process trees, and system wide scope works fundamentally differently from user specific scope.

Log files that are never rotated grow silently until a disk fills up and a production server crashes. logrotate keeps log files in check by size or time, compresses old files, and runs hooks such as service restarts after rotation. This article shows a practical configuration for a custom PHP application log and how to test it safely with debug mode before going live.

Every call to clock_gettime, every timestamp generated by MySQL, and every latency measurement in PHP-FPM depends on the Linux kernel's active clocksource. The Time Stamp Counter (TSC) is orders of magnitude faster than HPET on modern hardware, but was long known for synchronization problems across CPU cores that still produce false expectations and misconfigurations today.

A zombie process has already terminated, yet its parent process never collected its exit status, leaving a blocked entry in the process table. This guide explains the difference between zombies and orphaned processes, shows why kill -9 is completely ineffective, and gives concrete commands to find the responsible parent process and fix the problem permanently in code.

When a Linux server resolves domain names sometimes and not other times, the cause is rarely the DNS server itself but the local resolution chain in front of it: resolv.conf, systemd-resolved, nsswitch.conf, or a stubborn cache. This guide walks step by step through the correct order of checks, from the configuration file to the actual application runtime, and shows why a successful dig call alone proves nothing.

The official Magento system requirements list only names version numbers, yet a great deal of configuration work on the Linux server sits between those numbers and a working shop. This article translates PHP extensions, memory_limit, OpenSearch, Redis and Varnish into concrete commands and configuration files, and closes with a pre-flight checklist that catches setup mistakes before the first deployment.

A backup that has never actually been restored is an unproven assumption, not a reliable safety net. Automated restore tests regularly check whether a backup really works, whether the data is complete, and how long an actual restore takes. This article shows how to establish restore tests for Linux servers as a fixed, monitored part of operations.