htop — Interactive Process Viewer

What is htop?

htop is an interactive, cross-platform system monitor and process viewer for the terminal. It is a dramatically improved replacement for the traditional top command, adding colour, real-time filtering, mouse support, scrollable process lists, and a much more intuitive interface for managing running processes.

Whether you are investigating a slow server, identifying runaway processes, checking memory pressure, or just monitoring system health in real time, htop gives you a clear, at-a-glance picture of everything happening on your machine.

Why Use htop?

• Colourful, readable UI — CPU, memory, and swap usage rendered as visual bar graphs.
• Per-core CPU meters — see load on each individual CPU core at a glance.
• Mouse support — click to select processes, drag to resize columns.
• Interactive filtering — search and filter processes by name in real time.
• Tree view — visualize parent/child process relationships.
• Kill processes — send signals to processes without leaving the interface.
• Sort by any column — CPU, memory, PID, user, command, and more.
• Scrollable — scroll vertically and horizontally to see all processes.
• Configurable — customize the display, meters, and columns.

Installation

# Ubuntu / Debian
sudo apt update && sudo apt install htop

# macOS (Homebrew)
brew install htop

# Fedora / RHEL
sudo dnf install htop

# Arch Linux
sudo pacman -S htop

# Alpine Linux
apk add htop

# FreeBSD
pkg install htop

# Verify
htop --version

Basic Usage

Simply run htop to open the interactive monitor:

htop

# Monitor processes for a specific user
htop -u alice

# Set the update delay (in tenths of seconds, default 15 = 1.5s)
htop -d 5

# Show only processes matching a string (start with filter active)
htop -F "nginx"

Understanding the htop Interface

The htop interface has three main areas:

Header — System Meters

The top section shows:

• CPU bars — one bar per logical CPU core, coloured by usage type:
  • Blue: low-priority (nice) processes
  • Green: normal user processes
  • Red: kernel processes
  • Orange: I/O wait
• Memory bar — RAM usage (green = used, blue = buffers, yellow = cache)
• Swap bar — swap space usage
• Load average — 1, 5, and 15-minute averages
• Uptime — how long the system has been running
• Task count — total tasks, threads, and running processes

Process List

The main area shows all running processes with columns including:

Function Key Bar

The bottom bar shows available actions:

• F1 Help
• F2 Setup (configuration)
• F3 Search (filter by process name)
• F4 Filter
• F5 Tree view
• F6 Sort by column
• F7 Nice - (decrease priority)
• F8 Nice + (increase priority)
• F9 Kill (send signal)
• F10 Quit

Keyboard Shortcuts

💡 Tips & Tricks

Tip 1: Find the Highest CPU or Memory Consumer

Press P to sort by CPU percentage, or M to sort by memory. The hungriest process jumps to the top instantly.

Tip 2: Use Tree View to Understand Process Relationships

Press F5 or t to switch to tree view. Child processes are indented under their parents, making it easy to see which processes belong to a service, shell, or container.

Tip 3: Filter Processes by Name

Press F4 or \ and type a substring. The list filters in real time to show only matching processes. Useful for finding all nginx, node, or python workers.

Tip 4: Kill a Runaway Process

1. Navigate to the process with arrow keys (or use / to search by name).
2. Press F9 or k to open the signal menu.
3. Select SIGTERM (15) for a graceful stop, or SIGKILL (9) to force-kill.
4. Press Enter to send the signal.

Tip 5: Monitor a Specific User’s Processes

Press u and select a username from the list. htop will then show only that user’s processes.

Tip 6: Customize the Display

Press F2 to open the Setup menu. You can:

• Add or remove meters from the header
• Choose which columns appear in the process list
• Change colour themes
• Configure the update frequency

Tip 7: Tag Multiple Processes and Kill Them All

1. Navigate to a process and press Space to tag it (an asterisk appears).
2. Tag additional processes with Space.
3. Press F9 to send a signal to all tagged processes at once.

Advanced Applications

Find the Highest-Memory Process and Inspect It

# Sort by memory in htop (interactive)
htop
# Press M to sort by MEM%

# Alternatively, do this non-interactively from the command line:
# Show the top 10 memory-consuming processes
ps aux --sort=-%mem | head -n 11

# Get the PID of the top memory user
top_pid=$(ps aux --sort=-%mem | awk 'NR==2{print $2}')
echo "Top memory PID: $top_pid"

# Show detailed info about the process
cat /proc/$top_pid/status | grep -E "^(Name|VmRSS|VmSize|Threads)"

# Restart a specific service if it's consuming too much memory
pid=$(pgrep -f 'myservice')
if [ -n "$pid" ]; then
  kill -HUP $pid
  echo "Sent SIGHUP to $pid"
fi

Watch Resource Usage During a Build or Test Run

Open two panes in tmux — one running your build, one running htop — to see resource usage in real time:

# In tmux, split the window horizontally
# Ctrl+b, then "

# In the top pane, start htop
htop

# In the bottom pane, run your workload
npm run build

System Health Check Script

Use ps and related commands in shell scripts where htop is not available (or for automation):

#!/bin/bash
echo "=== System Resource Summary ==="
echo ""
echo "Load averages:"
uptime

echo ""
echo "Memory:"
free -h

echo ""
echo "Top 5 CPU-consuming processes:"
ps aux --sort=-%cpu | awk 'NR<=6 {printf "%-10s %-6s %-6s %s\n", $1, $2, $3, $11}'

echo ""
echo "Top 5 memory-consuming processes:"
ps aux --sort=-%mem | awk 'NR<=6 {printf "%-10s %-6s %-6s %s\n", $1, $2, $4, $11}'

echo ""
echo "Disk usage:"
df -h | grep -v tmpfs

Alternatives and Related Tools

Related Resources

• 🔧 htop Official Website
• 📦 htop GitHub Repository
• 📖 Linux ps Manual

Related Tools

• ps — static process snapshot; perfect for scripting.
• top — the original, pre-installed on every Unix system.
• tmux — run htop in a persistent tmux pane alongside your development work.

Real-world Use Cases

• Incident investigation — quickly spot the runaway process consuming 100% CPU or exhausting RAM on a production server.
• Development profiling — watch memory and CPU usage in real time while running a build, test suite, or data processing job.
• Container monitoring — run htop inside a container to inspect its processes when docker stats isn’t detailed enough.
• Server capacity planning — observe real-world resource usage under load to decide when to scale up or add more instances.
• Process tree debugging — use tree view to understand parent/child relationships, especially for daemons, workers, and forking servers.

When Not To Use htop

• Scripting and automation — htop is interactive; use ps, top -bn1, or /proc filesystem for scriptable process information.
• Remote monitoring dashboards — use Prometheus + Grafana, Datadog, or similar for persistent metrics and alerting.
• Containers in CI — container environments often lack a TTY; use ps aux or structured JSON logs instead.
• Windows — htop is Unix-only; use Task Manager or Get-Process in PowerShell on Windows.

Practical Examples: Monitor Processes Interactively and from Scripts

# 1. Start htop filtered to a specific process group
htop -F "node"

# 2. Script: alert if any process exceeds 80% memory
threshold=80
while true; do
  high_mem=$(ps aux --sort=-%mem | awk 'NR>1 && $4+0 > '"$threshold"' {print $1, $2, $4"%", $11}')
  if [ -n "$high_mem" ]; then
    echo "HIGH MEMORY ALERT:"
    echo "$high_mem"
  fi
  sleep 30
done

# 3. Snapshot the top 5 processes to a log file every minute
while true; do
  echo "=== $(date -Iseconds) ===" >> /var/log/process-snapshot.log
  ps aux --sort=-%cpu | head -6 >> /var/log/process-snapshot.log
  sleep 60
done