htop

What is htop?

htop is an interactive text-mode process viewer for Linux, a powerful alternative to the standard top command. Unlike top, which requires constant scrolling to view all processes, htop offers a dynamic, navigable interface. You can scroll through processes, sort by various metrics, kill processes, and even change process priorities – all without leaving the command-line.

Installation

htop is not typically included in minimal Linux installations. To install it, you’ll need to use your distribution’s package manager. Here are examples for some popular distributions:

• Debian/Ubuntu:

  sudo apt update
  sudo apt install htop

• Fedora/CentOS/RHEL:

  sudo dnf install htop

• Arch Linux:

  sudo pacman -S htop

Once installed, simply type htop in your terminal and press Enter to launch the application.

Navigating the htop Interface

The htop interface displays information in a clear, organized manner. Key elements include:

• Top Section: Displays system-wide statistics like CPU usage (per core), memory usage, swap space, and load average.
• Main Section: Shows a list of running processes with their PID, user, CPU and memory usage, and more.
• Bottom Section: Provides navigation instructions and quick access to commands.

Key Navigation Commands

• Arrow Keys: Navigate up and down the process list.
• Spacebar: Sorts processes by CPU usage (cycles).
• F6: Switch between different sorting options (e.g., CPU%, MEM%, PID, etc.).
• F4: Filter processes by name or part of a name. (Type your filter, then press Enter)
• K: Send a KILL signal (SIGTERM) to a selected process. This politely requests the process to terminate.
• Shift+K: Send a KILL signal (SIGKILL) to a selected process. This forces the process to terminate. Use with caution!
• H: Shows the tree view of processes, highlighting parent-child relationships
• F2: Change settings (colors, display options).

Example: Monitoring CPU Usage

Let’s say you suspect a specific process is consuming excessive CPU resources. After launching htop, you can:

1. Identify the process: Use the arrow keys to navigate to the suspect process in the process list. Observe its CPU % usage.
2. Sort by CPU usage: Press the Spacebar to sort the list by CPU percentage, making high-CPU consumers easier to spot.
3. Kill the process (if necessary): If the process is unresponsive or misbehaving, press K (SIGTERM) or Shift+K (SIGKILL) to terminate it.

Example: Analyzing Memory Usage

Similar to CPU monitoring, you can effectively analyze memory usage with htop.

1. Sort by memory usage: Press F6 to select “MEM%” as the sorting criteria. This displays the processes consuming the most RAM at the top.
2. Identify memory leaks: If you see processes consistently consuming large amounts of RAM, investigate potential memory leaks within those applications.

Example: Filtering Processes

Finding a specific process in a long list can be tedious. htop’s filtering feature is helpful:

1. Press F4: This activates the filter input field.
2. Enter a filter string: For instance, if you are searching for a process named ‘chrome’, type ‘chrome’ and press Enter. htop will display only processes containing ‘chrome’ in their name.

Beyond the Basics

htop offers many more features, including customizable display settings, interactive process management, and real-time monitoring. Exploring its options through the help menu (usually accessible via F1) is highly recommended for advanced usage. Its intuitive interface and powerful features make it an indispensable tool for any Linux system administrator or developer.