4.1 Linux administration

21 entries match these filters

• 0420 cron and systemd timers: run something every night Schedule a script with crontab or a systemd timer: the five cron fields, environment and PATH pitfalls, logging, catching up missed runs… Beginner · Step by step · Linux Article cron & timers · Services & systemd 15 Oct 2026
• 0352 Harden a fresh Linux server in 30 minutes The baseline for any new Debian, Ubuntu or RHEL-family server: updates on, a non-root user with sudo, SSH keys only, a firewall… Beginner · Step by step · Linux Article Server hardening · Users, sudo & hardening 15 Oct 2026
• 0344 ufw and firewalld: open and close ports Allow and remove ports and services on the two standard Linux host firewalls, restrict a port to one source network, and make… Beginner · Step by step · Linux Article Firewalls · Networking & firewalls 15 Oct 2026
• 0320 Fix: address already in use (EADDRINUSE) Something is already listening on the port your program wants. Find the process with lsof or ss, stop it or pick another… Beginner · Fixes an error · Linux, macOS Article Networking & firewalls · Node.js · Processes & ports 15 Oct 2026
• 0342 Which process is using a port, and how to free it Find the program behind a busy port with ss, lsof or fuser, decide whether to stop it properly or kill it, and… Beginner · Step by step · Linux, macOS Article DNS, IP addresses & ports · Networking & firewalls 15 Oct 2026
• 0321 Fix: E: Unable to locate package / could not get lock /var/lib/dpkg/lock Two apt errors with simple causes: Unable to locate package means the package lists are stale or the name is wrong; could… Beginner · Fixes an error · Linux Article Packages & updates 15 Oct 2026
• 0328 Install Docker Engine on Ubuntu and Debian Set up Docker's official apt repository, install Docker Engine with the Compose and Buildx plugins, run hello-world and let your user run… Beginner · Step by step · Linux Article Docker basics · Packages & updates 15 Oct 2026
• 0323 Fix: Failed to start service, how to read systemctl status and journalctl Job for x.service failed tells you only that the service did not start. The real reason is in systemctl status and journalctl… Beginner · Fixes an error · Linux Article Logs · Services & systemd 15 Oct 2026
• 0322 Fix: user is not in the sudoers file sudo refuses because your account is not allowed to use it. Add the user to the sudo group (Debian, Ubuntu) or wheel… Beginner · Fixes an error · Linux, macOS Article Server hardening · Users, sudo & hardening 15 Oct 2026
• 0309 What is RAID? RAID combines several disks into one so data survives a disk failure or is read and written faster. Beginner · Explains an idea · Any system Article Disks, LVM & filesystems 15 Oct 2026
• 0316 Fix: command not found bash: something: command not found means the shell could not find a program with that name in any PATH directory. The usual… Beginner · Fixes an error · Linux, macOS Article Basics · Packages & updates 15 Oct 2026
• 0317 Fix: Permission denied when running a script (chmod +x) bash: ./script.sh: Permission denied means the file exists but you may not execute it. Usually the execute bit is missing; sometimes the… Beginner · Fixes an error · Linux, macOS Article Basics · Users, sudo & hardening 15 Oct 2026
• 0281 What is a package manager? A package manager is a tool that installs, updates and removes software for you and keeps track of what depends on what. Beginner · Explains an idea · Any system Article Packages & updates 15 Oct 2026
• 0288 What is a daemon or service? A daemon or service is a program that runs in the background all the time, waiting to do its job without a… Beginner · Explains an idea · Any system Article Services & systemd 15 Oct 2026
• 0249 Set up and harden a fresh Linux server in one afternoon Take a new Ubuntu, Debian or Rocky/Alma server from first login to a safer baseline: sudo admin, SSH keys only, firewall, automatic… Beginner · Guided project · Linux Article Networking & firewalls · Packages & updates · Users, sudo & hardening 15 Oct 2026
• 0172 Fix: No space left on device Writes fail because a filesystem is full, out of inodes, or holding space for deleted files that are still open. Find which… Beginner · Fixes an error · Linux Article Disks, LVM & filesystems 15 Oct 2026
• 0174 Network and DNS troubleshooting commands: ip, ss, dig, resolvectl A layer-by-layer cheat sheet for "the server cannot reach X": interfaces and routes with ip, listening ports with ss, and name resolution… Beginner · Cheat sheet · Linux Article Networking & firewalls 15 Oct 2026
• 0176 apt vs dnf: package commands and automatic security updates The everyday package commands on Debian/Ubuntu (apt) and RHEL/Rocky/Alma (dnf) side by side, plus how to turn on automatic security updates on… Beginner · Cheat sheet · Linux Article Packages & updates 15 Oct 2026
• 0177 Users, groups and sudo on Debian, Ubuntu and RHEL How Linux accounts and groups work, how to create users, and how sudo gives admin rights through the sudo group on Debian/Ubuntu… Beginner · Explains an idea · Linux Article Users, sudo & hardening 15 Oct 2026
• 0164 systemd services: systemctl and journalctl basics systemd starts and supervises services on most Linux servers. systemctl starts, stops and enables them; journalctl shows their logs. Beginner · Explains an idea · Linux Article Services & systemd 15 Oct 2026
• 0099 Proxmox VE repositories and updates: enterprise vs no-subscription A fresh Proxmox VE install uses the enterprise repository, which needs a subscription. Learn how to switch to the no-subscription repository and… Beginner · Step by step · Linux Article Installation & first steps · Packages & updates 15 Oct 2026