Page 5 - Linux

Job control is far more than Ctrl-Z followed by a quick bg. Understanding how Bash manages jobs, process groups and signals lets you run long migrations, backups and maintenance tasks in the background without a dropped SSH session dragging all that progress down with it.

Without active traffic shaping, every service on a server shares available bandwidth on a first come, first served basis, which typically means nightly backup runs make production HTTP responses noticeably slower. Linux Traffic Control with tc and the right qdisc types lets you cap bandwidth per service, port, or IP address and enforce priorities cleanly.

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.

Several gigabytes of swap usage while free -h simultaneously reports plenty of free memory looks paradoxical, but is usually proactive, intentional kernel behavior rather than a fault. This guide shows how to use Pressure Stall Information, vmstat, and smaps to distinguish harmless from actually problematic swapping, what role swappiness really plays, and when MySQL buffer pool configuration is the actual cause.

Anyone who has set an environment variable in an SSH session only to find it missing inside a cron job knows this problem well. Bash loads a completely different set of startup files depending on context. The load order of profile, bash_profile and bashrc decides which configuration actually takes effect, and this exact detail is where most administrators get stuck.

SSH is the most important gateway for server access, and also one of the most heavily automated attack targets on the internet. This article shows how key-based authentication with ed25519, disabled root login, fail2ban, and a hardened sshd_config reliably block brute-force attacks, rounded out with bastion host patterns for secure access to production servers.

A crontab entry is only the beginning of a cron job. Without locking, jobs run in parallel. Without logging, errors disappear. Without monitoring, a broken cron job can run unnoticed for weeks. flock, structured logging, exit code checks and systemd timers turn fragile cron calls into reliable, observable automation units.

Anyone who steers systemd services by trial and error wastes valuable time during outages in production. systemctl starts, stops and monitors services reliably, reads status output correctly, and recognizes states like failed or activating instantly and without guesswork. journalctl then delivers the matching, filtered logs for fast troubleshooting in production Linux environments and Magento deployments.

The five fields of a crontab line look simple at first glance, yet lists, ranges, steps, and above all the notorious OR logic between day of month and weekday regularly produce jobs that run at the wrong time or not at all. This guide explains crontab syntax completely, including special characters, environment variables, and timezones.