How to Fix "Permission denied (publickey)" in SSH
A step-by-step checklist to fix the SSH "Permission denied (publickey)" error: wrong user, missing key, bad permissions and server settings.
yuri@itblogs: ~
$ cat README.md # Personal IT knowledge base Fixes, snippets and notes from real-world work: Linux, networking, servers, DevOps. $ ls posts/ | wc -l 16$
Secure a New Ubuntu 24.04 Server: The First 10 Steps
A practical hardening checklist for a fresh Ubuntu server: SSH keys, firewall, fail2ban, automatic updates and backups, in about 15 minutes.
Cloudflare 521, 522 and 525 Errors: How to Fix Them
What Cloudflare 521, 522, 523, 524, 525 and 526 errors mean and how to find the cause: firewall, SSL mode, certificates and DNS.
Linux Disk Full: How to Find What Is Using the Space
Find out why a Linux disk is full: df, du, ncdu, inodes, logs, Docker, deleted-but-open files and safe ways to clean up.
Which Process Is Using a Port on Linux? (ss, lsof, fuser)
Find and stop the process holding a port on Linux with ss, lsof and fuser, and fix "Address already in use" errors.
Git Undo Cheat Sheet: Fix Almost Any Mistake
How to undo commits, discard changes, fix the wrong branch, recover lost work with reflog and remove pushed mistakes safely.
Install Apache, PHP-FPM and MariaDB (LAMP) on Ubuntu 24.04
A clean LAMP setup on Ubuntu 24.04 with PHP-FPM: virtual host, secure MariaDB, permissions, HTTPS with Let's Encrypt and troubleshooting.
Linux File Permissions Explained: chmod, chown and umask
Understand rwx, octal modes, chmod, chown, setgid, sticky bit and umask, and debug "Permission denied" with namei.
How to Install Docker on Ubuntu 24.04 (Official Repository)
Install the latest Docker Engine and Compose on Ubuntu 24.04 from the official repository, with post-install steps, log limits and security notes.
Docker Cheat Sheet: Essential Commands and Troubleshooting
The Docker commands you use every day: run, logs, exec, build, volumes, cleanup, plus how to fix containers that exit or are unreachable.
Docker Compose Tutorial: Run a Multi-Container App
Learn Docker Compose with a real example: a web service and MariaDB with volumes, healthchecks, .env secrets, updates and backups.
Docker and UFW: Why Published Ports Bypass Your Firewall
Docker ignores UFW rules for published ports. Learn why it happens and how to fix it with localhost binding, DOCKER-USER rules and provider firewalls.
Bash Scripting Cheat Sheet: Variables, Loops, Functions and More
A practical Bash reference: variables, arguments, conditions, loops, functions, arrays, string handling, redirects and exit codes with examples.
Write Safer Bash Scripts: set -euo pipefail, trap and ShellCheck
Make Bash scripts fail safely: strict mode, quoting, trap cleanup, mktemp, flock, dry-run mode and ShellCheck, with a reusable template.
Useful Bash One-Liners for Sysadmins and Developers
Handy shell one-liners for finding files, analyzing logs, processing text, renaming in bulk, monitoring the system and moving data.