Use lsof -i :PORT or ss -tlnp | grep PORT. For example, lsof -i :8080 shows the process name and PID occupying port 8080.

Use tail -f /path/to/file.log. New lines appear as they are written. Combine with grep: tail -f app.log | grep ERROR to filter by keyword.

Use grep -r "keyword" /path/to/dir/. Add -n for line numbers, -i for case-insensitive search, -l to list only filenames.

755 grants the owner read/write/execute and group/others read/execute — used for directories and executables. 644 grants the owner read/write and others read-only — used for config files and web assets.

Use nohup command > output.log 2>&1 & or start a tmux/screen session. The process continues running on the server after the terminal is closed.

Use find . -mtime -1 -type f to find files modified in the last 24 hours. Use -mtime -7 for the last 7 days. Add -ls to show details.