htop

What is htop?

htop is an interactive text-mode process viewer for Linux, offering a dynamic and user-friendly alternative to the static top command. It provides a real-time overview of system processes, CPU usage, memory consumption, and more, all within a navigable interface. Unlike top, htop doesn’t require constant screen refreshing – you can navigate and interact with the displayed information directly.

Installation

htop is not typically included in minimal Linux installations. You’ll need to install it using your distribution’s package manager. Here are examples for common distributions:

• Debian/Ubuntu:

sudo apt update
sudo apt install htop

• Fedora/CentOS/RHEL:

sudo dnf install htop

• Arch Linux:

sudo pacman -S htop

Navigating the htop Interface

After installation, simply run htop in your terminal. You’ll be greeted with a screen displaying various system metrics. The key elements include:

• Top Section: Shows overall system information like CPU usage, memory usage, swap usage, and load average.
• Process List: Displays a list of running processes with details such as PID, user, CPU%, memory%, and command.
• Bottom Section: Provides navigation and interaction options.

Navigation Keys:

• Arrow Keys: Move the cursor within the process list.
• Spacebar: Sort the process list by the selected column.
• F6: Filter the displayed processes. You can use this to focus on processes run by a specific user, or those matching specific patterns. For Example: To filter process for user “john” type “john” in the filter popup.
• F2: Provides various configuration options. You can enable/disable certain features like the tree view (which shows parent-child process relationships) and change the refresh rate.
• F4: Allows you to kill selected process by entering the Process ID (PID).
• F9: Allows you to run a new process.
• F10: Exits htop.

Practical Examples: Analyzing System Performance

Let’s illustrate htop’s utility with some scenarios:

1. Identifying CPU-Intensive Processes:

Imagine a situation where your system is sluggish. Running htop will immediately highlight processes consuming significant CPU resources. The %CPU column readily indicates the culprit. You can then take appropriate action, like investigating the process, prioritizing it, or even killing it if necessary (use with caution!).

2. Detecting Memory Leaks:

Memory leaks can gradually degrade system performance. htop’s memory usage columns (%MEM, RES, VIRT) allow you to track memory consumption by individual processes and identify potential memory leaks. High RES (resident memory) usage, particularly with consistently increasing memory usage over time, might point to a problem.

3. Monitoring Disk I/O:

While htop doesn’t directly show detailed disk I/O, observing overall CPU usage and the presence of processes with high %CPU alongside potentially slow processes might be indirect indicators of I/O bottleneck.

4. Analyzing Process Tree: (Requires enabling the tree view in htop’s configuration)

With the tree view enabled, htop provides a visual representation of the process hierarchy. This is helpful for understanding process relationships and identifying processes indirectly impacting system performance. For instance, a high-CPU consuming process might have many child processes contributing to the load.

Beyond the Basics

htop offers many additional features and options worth exploring, such as customizing the displayed columns, setting alerts, and integrating with external monitoring tools. Refer to the htop man page (man htop) for an overview of its features. The built-in help section (often accessible with F1) is also a great starting point.