top
top is the classic process viewer and system monitoring utility found on virtually every Unix-like operating system. It provides a real-time, full-screen view of running processes, system resource usage, and uptime information. As the oldest and most widely deployed system monitor, top is the standard tool that administrators reach for when a system feels slow or a process appears stuck.
Key Features
- Real-time process list — Continuously updated list of running processes
- CPU and memory usage — Per-process CPU and memory utilisation with sortable columns
- System summary — Uptime, load average, task count, CPU states, and memory totals
- Interactive commands — Sort by CPU, memory, PID, or time with keyboard shortcuts
- Process management — Send signals (kill, renice) to running processes
- Customisable display — Show or hide fields, change sort order, set update frequency
- Colour mode — Configurable color coding for different states and processes
- Batch mode — Non-interactive output for logging and scripting via -b flag
Why Use It
top is the universal starting point for system diagnostics. It is pre-installed on every Linux distribution, works reliably, and provides the essential information needed for 90 per cent of troubleshooting scenarios. Even with more modern alternatives like htop and btop, top remains the tool that is always available and always works.
Use Cases
- Immediate system check — First tool to run when investigating performance issues
- Process identification — Find CPU or memory-intensive processes by PID and user
- Load average monitoring — Check system load and CPU utilisation at a glance
- Scripted monitoring — Log process data over time with batch mode
Platform
Linux, macOS, BSD, all Unix-like systems
Licence
GNU General Public License v3.0 (Linux version — procps-ng)