htop Command in Linux: Monitor Processes Interactively

When a server starts responding slowly or a desktop session feels sluggish, you need to figure out which process is consuming the most CPU or memory. The top command can do this, but its interface is minimal and navigation takes some getting used to. htop is an interactive process viewer that improves on top with color-coded meters, mouse support, and the ability to scroll, search, filter, and kill processes without leaving the viewer.

This guide explains how to install and use htop to monitor system resources and manage processes on Linux.

Installing htop #

htop is available in the default repositories of most Linux distributions but is not always pre-installed.

On Ubuntu, Debian, and Derivatives:

sudo apt install htop

On Fedora, RHEL, and Derivatives:

sudo dnf install htop

Verify the installation by checking the version:

htop --version

htop 3.4.1

htop Syntax #

htop [OPTIONS]

Running htop without arguments opens the interactive process viewer with default settings:

htop

Understanding the Interface #

The htop screen is divided into three areas: a header with system meters, a process list in the center, and a footer with function key shortcuts.

Header Area #

The top section shows system-wide resource usage at a glance:

• CPU bars: one bar per CPU core, color-coded by usage type. Green is normal user processes, red is kernel (system) activity, blue is low-priority (nice) processes, and cyan is virtualization overhead (steal time)
• Memory bar: shows used, buffered, and cached memory as a proportion of total RAM. Green is memory in use by applications, blue is buffers, and yellow is file cache
• Swap bar: shows swap usage. If this bar is consistently full, the system does not have enough physical memory for its workload
• Tasks: total number of processes and threads, with a count of how many are currently running
• Load average: the 1-minute, 5-minute, and 15-minute system load averages
• Uptime: how long the system has been running since the last boot

Process List #

Below the header, each row represents one process. The default columns are:

• PID - process ID
• USER - the owner of the process
• PRI - kernel scheduling priority
• NI - nice value (user-space priority, ranges from -20 to 19)
• VIRT - total virtual memory the process has allocated
• RES - resident memory, the portion of physical RAM the process is actually using
• SHR - shared memory, the portion of RES that is shared with other processes (such as shared libraries)
• S - process state (R running, S sleeping, D uninterruptible sleep, Z zombie, T stopped)
• CPU% - percentage of CPU time the process is using
• MEM% - percentage of physical memory the process is using
• TIME+ - total CPU time consumed since the process started
• Command - the full command line that launched the process

Function Keys #

The bottom bar shows the available actions:

• F1 - open the help screen
• F2 - open the setup menu to customize meters and columns
• F3 - search for a process by name
• F4 - filter the process list to show only matching entries
• F5 - toggle tree view
• F6 - choose a column to sort by
• F7 - decrease the nice value (higher priority) of the selected process
• F8 - increase the nice value (lower priority) of the selected process
• F9 - send a signal to the selected process
• F10 - quit htop

Sorting Processes #

By default, htop sorts processes by CPU usage, so the heaviest processes float to the top. To change the sort column, press F6 and select a column from the list using the arrow keys.

For quick sorting without opening the menu, use these shortcut keys:

• P - sort by CPU%
• M - sort by MEM%
• T - sort by TIME+

Press the same key again to reverse the sort order. This is useful when you want to find the least active processes or the ones that started most recently.

You can also set the initial sort column from the command line:

htop -s PERCENT_MEM

This starts htop with the process list sorted by memory usage, which is handy when you are investigating high memory consumption on a server.

Searching for a Process #

Press F3 (or /) to open the search bar at the bottom of the screen. Type part of the process name and htop will highlight the first matching entry in the process list. Press F3 again to jump to the next match.

The search is incremental, so the highlight updates as you type each character. Press Esc to close the search bar and return to normal navigation.

Filtering Processes #

Press F4 to activate the filter. Unlike search, which jumps between matches, filtering hides all processes that do not match the text you type. Only matching entries remain visible in the list.

This is especially useful on busy systems with hundreds of running processes. For example, typing postgres after pressing F4 reduces the list to only PostgreSQL worker processes and the postmaster, making it much easier to see their combined resource usage.

Press Esc to clear the filter and restore the full process list.

Tree View #

Press F5 to toggle tree view. In this mode, htop groups child processes under their parent and displays the process hierarchy as an indented tree. This makes it straightforward to see which processes were spawned by a service manager, a shell session, or a container runtime.

To start htop in tree view directly from the command line:

htop -t

Tree view combines well with filtering. Press F4, type a service name, and the tree shows only that service and its child processes. For a dedicated look at process hierarchies outside of htop, see the pstree command .

Killing a Process #

To stop a process from within htop, use the arrow keys to highlight it (or search with F3), then press F9. This opens a signal selection menu on the left side of the screen.

The most commonly used signals are:

• 15 SIGTERM - asks the process to shut down gracefully. This is the default and the safest first choice
• 9 SIGKILL - forces the process to terminate immediately. Use this only when SIGTERM does not work, because the process gets no chance to clean up
• 2 SIGINT - the same signal sent by pressing Ctrl+C in a terminal
• 1 SIGHUP - often used to tell a daemon to reload its configuration without restarting

Select the signal with the arrow keys and press Enter to send it. For more detail on process signals and how to send them from the command line, see the kill command guide .

You can also tag multiple processes with Space and then press F9 to send a signal to all of them at once. Press U to untag all processes when you are done.

Changing Process Priority #

You can adjust the scheduling priority (nice value) of a process directly from htop. Select the process and press:

• F7 - decrease the nice value (give the process higher priority)
• F8 - increase the nice value (give the process lower priority)

Nice values range from -20 (highest priority) to 19 (lowest priority). Only root can set negative nice values, so you will need to run htop with sudo to raise a process above normal priority.

This is useful when a background task like a large compilation is consuming too much CPU and you want to lower its priority so that interactive services remain responsive.

Showing Only One User’s Processes #

To limit the process list to a single user, start htop with the -u option:

htop -u www-data

This shows only processes owned by www-data, which is useful when you are debugging a web server or an application service and do not want system processes cluttering the view.

Monitoring Specific Processes #

To watch a known set of processes by their PIDs, use the -p option:

htop -p 1234,5678

The display is restricted to those two processes, but the header meters still show system-wide resource usage. This gives you a focused view while keeping overall load visible at the top.

Customizing the Display #

Press F2 to open the setup screen. From here you can:

• Rearrange the header meters (move CPU bars, swap positions, switch between bar, text, graph, or LED display styles)
• Add or remove columns in the process list
• Change the color scheme
• Toggle display options like showing kernel threads or custom thread names

Changes are saved to ~/.config/htop/htoprc and persist across sessions.

Command-Line Options #

• -d N - set the update interval to N tenths of a second. For example, -d 20 updates every 2 seconds instead of the default 1.5 seconds
• -u USER - show only processes belonging to USER
• -p PID[,PID...] - show only the specified process IDs
• -t - start in tree view
• -s COLUMN - sort by the given column name (use names like PERCENT_CPU, PERCENT_MEM, TIME)
• -C - use monochrome mode (no colors), useful on terminals with limited color support
• -H - highlight new and old processes

Quick Reference #

For a printable quick reference, see the htop cheatsheet .

Troubleshooting #

htop: command not found
htop is not installed by default on every distribution. Install it with your package manager: sudo apt install htop on Debian-based systems or sudo dnf install htop on Fedora and RHEL.

Cannot change process priority (permission denied)
Setting a nice value below 0 requires root privileges. Run htop with sudo to adjust priority for processes owned by other users or to set negative nice values.

CPU bars show unexpected colors
Each color represents a different type of CPU usage. Green is normal user processes, red is kernel activity, blue is low-priority (nice) processes, and cyan is virtualization steal time. Press F1 inside htop to see the full color legend for your version.

Memory bar looks full but the system is responsive
Linux uses free memory for disk cache and buffers. The memory bar in htop distinguishes between application memory (green), buffers (blue), and cache (yellow). Cached memory is released to applications when they need it, so a full-looking bar does not mean the system is out of memory.

Processes appear and disappear quickly
Short-lived processes can start and exit between screen refreshes. Lower the update interval with -d 5 (half a second) to catch fast processes. Keep in mind that a very short interval increases the CPU usage of htop itself.

FAQ #

What is the difference between htop and top?
Both show running processes and system metrics in real time. htop adds color-coded CPU and memory meters, mouse support, horizontal and vertical scrolling, built-in search and filtering, and the ability to kill or renice processes without typing a PID. The top command is pre-installed on virtually every Linux system, while htop may need to be installed separately.

Does htop use more resources than top?
Slightly. htop reads additional process details from /proc, so it uses a bit more CPU and memory than top. On modern hardware the difference is negligible, even on systems with thousands of processes.

What do VIRT, RES, and SHR mean?
VIRT is the total virtual memory the process has mapped, including memory it has allocated but may not be using yet. RES (Resident) is the portion actually held in physical RAM. SHR (Shared) is the subset of RES that is shared with other processes, such as shared libraries loaded by multiple programs.

How do I save my htop configuration?
Press F2 to open the setup screen, make your changes, and press F10 to exit. htop saves the configuration automatically to ~/.config/htop/htoprc.

Can I run htop over SSH?
Yes. htop works in any terminal emulator, including SSH sessions. If you are monitoring a remote server over a long session, consider running htop inside screen or tmux so the session persists if the connection drops.

Conclusion #

htop gives you a clear, interactive view of what is running on your system and the resources each process is consuming. For related tools, see the ps command for snapshot process listings, kill for sending signals from the command line, and pstree for visualizing the process hierarchy.

About the authors

Dejan Panovski

Dejan Panovski is the founder of Linuxize, an RHCSA-certified Linux system administrator and DevOps engineer based in Skopje, Macedonia. Author of 800+ Linux tutorials with 20+ years of experience turning complex Linux tasks into clear, reliable guides.

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