Page 2 - Linux

The wrong CPU governor forces a server to ramp up its clock speed on every incoming request before it can actually respond. This delay is barely visible in monitoring, but shows up in practice as fluctuating response times, especially under bursty PHP-FPM traffic.

When a server simply reboots after a kernel panic, the actual cause stays in the dark until the same crash happens again. kdump automatically produces a complete memory dump when a kernel panic hits, and the crash utility turns that vmcore into something readable, with a backtrace, process state and the exact spot in the kernel code where it broke.

A server suddenly can no longer reach a payment provider, an external API, or an internal service, and the error message Connection timed out says nothing about the cause. This article shows the complete diagnostic path for a failing network connection: DNS, routing, firewall, TCP handshake and application layer, each with the appropriate command for that layer.

Alongside the system clock the kernel keeps in memory, almost every physical and virtual machine has a battery backed hardware clock that keeps running even while the machine is powered off. Anyone who does not know the difference between the system clock and the hardware clock will sooner or later be puzzled by wrong boot timestamps, mistimed certificate checks, or a dual boot system that shows a different time after every Windows startup. This article explains how hwclock works, how to set the hardware clock correctly, and how to keep it reliably synchronized with the system clock.

High system load is not automatically a sign of a slow disk. This guide shows how iostat with interval sampling separates real trends from short bursts, how iotop identifies the specific process behind heavy I/O usage, and how metrics like %util and await reliably reveal whether you are looking at a disk problem or an application problem.

Planning server storage around rigid partitions runs into limits the moment you need to grow. LVM decouples logical volumes from the physical disk layout and lets you resize, snapshot, and add new disks while the application keeps running, with no restart required.

The EMFILE error, reported as "Too many open files", is rarely a coincidence and almost never a pure capacity issue. Usually an application opens connections, files, or sockets and never closes them again. This guide shows how to use lsof, the /proc/pid/fd directory, and targeted monitoring to find out which code path is leaking file descriptors and how to configure the limits correctly without papering over the actual leak.

An OnCalendar expression looks like a simple date at first glance but can combine weekdays, ranges, lists and repeats in a single, compact line. Anyone who does not really understand the syntax copies examples from the internet and then wonders why the timer never fires or fires at the wrong time. This article explains the OnCalendar syntax systematically, from simple shorthands to complex expressions, and shows how to reliably test every expression before deployment with systemd-analyze calendar.

Running Linux servers with shared logins and unmaintained accounts risks security gaps that only surface after an incident. This article explains useradd, usermod and groupadd from the ground up, shows the principle of a dedicated unprivileged user per application and provides a practical workflow to systematically audit existing users and groups on a server.

Every session_start() call, every TLS connection, and every CSRF token generated in PHP needs random bytes from the operating system. If the kernel's collected entropy is insufficient, the affected calls block until enough random data is available, an effect that occurs especially often on virtual machines and in containers, showing up as hard to explain, sporadic latency spikes.