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Linux tutorials
Check and manage running services on Linux with systemctl
Learn how to check running services on Linux, start, stop and restart them, enable them at boot, and read their logs with journalctl using systemctl on any systemd-based distro.
Fix Redis OOM command not allowed when used memory greater than maxmemory
Learn why Redis throws OOM command not allowed when used memory greater than maxmemory, how to diagnose it with redis-cli and free -m, and how to fix it by setting a sane maxmemory and eviction policy.
Find and view hidden files and directories on Linux
Learn how hidden files and dotfiles work on Linux, list them with ls -a and ls -la, find them with the find command, and view them in GUI and terminal file managers like ranger and mc.
Fix SSH Too many authentication failures error on Linux
Learn why SSH rejects you with too many authentication failures and how to fix it on the client with IdentitiesOnly and IdentityFile, manage ssh-agent keys correctly, and safely raise MaxAuthTries on servers you control.
Find out which process is using all your CPU or memory on Linux
Learn how to identify which process is consuming your Linux server's CPU or memory using top, ps aux, and sort, then safely terminate runaway or zombie processes without guessing.
Fix apt update E: Repository no longer has a Release file
Learn why apt update fails with the Release file error on Ubuntu and Debian, how to find the broken repository entry, and how to fix it safely, including EOL releases and GPG key issues.
Check disk space usage on Linux with df and du commands
Learn how to check disk space on Linux using df and du, find large files and directories, spot hidden disk usage from deleted but open files, and troubleshoot common out-of-space problems.
Find and kill processes using a specific port on Linux
Learn how to find which process is using a specific port on Linux, identify its owner safely, and kill it with the right tool. Covers lsof, ss, fuser, and how to prevent address already in use errors for good.
Fix PostgreSQL FATAL sorry, too many clients already
Learn why PostgreSQL throws FATAL: sorry, too many clients already, how to check and close idle connections, safely raise max_connections, and prevent the error from coming back with connection pooling.
Configure Linux file and directory ownership with chown and security best practices
Learn to properly configure file and directory ownership using chown, understand user and group permissions, and implement secure ownership patterns for web servers and applications.
Fix SSH sign_and_send_pubkey: signing failed: agent refused operation
Resolve SSH authentication errors when the SSH agent refuses to sign public keys. This tutorial covers checking agent status, fixing key permissions, restarting the agent, and troubleshooting SSH client configuration.
Configure Linux swap space with memory management and performance optimization
Set up and optimize Linux swap space for better system performance. Learn to create swap files, configure swappiness parameters, and monitor memory usage across different Linux distributions.