Raspberry Pi

Why Is My Raspberry Pi Slow? Monitoring Performance with Htop

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After you’ve had your Raspberry Pi for a while and you’ve made it run a web server, media centre, Remote Desktop and more, you might find it’s becoming a bit sluggish. To diagnose performance issues and identify resource-hungry processes, there’s a brilliant tool called htop that can help.

Understanding System Performance

Traditionally in Linux, you would use the top command to view system processes and resource usage. However, this generally needs a bit more know-how to interpret the display, and it looks rather plain and difficult to parse at a glance.

Introducing Htop: A Better Process Viewer

An ideal replacement for top is ‘htop’, developed by Hisham Muhammad. This is an excellent process viewer with simple colour coding and a graphical output to show where resources might be used. Here’s a sample screenshot from my Pi:

Screen-Shot-2016-02-10-at-00.20.32 htop – a process viewer for the Raspberry Pi

Installing Htop on Your Raspberry Pi

Installation is straightforward. Simply open a terminal and enter:

sudo apt-get update
sudo apt-get install htop

That’s it! It’s extremely easy to install and has no real overhead when running, making it suitable even for resource-constrained devices like the Raspberry Pi.

Understanding the Htop Display

CPU Usage

At the top of the display, the numbers 1, 2, 3, 4 represent each processor core’s status (for multi-core models like the Raspberry Pi 4; older models will show fewer cores). The more a core is in use, the further the corresponding graph extends to the right. Different colours indicate different types of processes:

  • Blue: Low-priority processes
  • Green: Normal user processes
  • Red: Kernel processes

Memory Usage

The Mem/Swp bars show the utilisation of your RAM and Swap space:

  • RAM (Memory): Linux typically fills RAM for caching, so seeing high utilisation isn’t necessarily a problem. What’s important is the breakdown of used versus cached memory.
  • Swap: This is virtual memory on your SD card. Your swap should not be used too much—if it is, your system will often slow down as it swaps memory between the disk (or SD card) and RAM as required. Heavy swap usage is a key indicator that you need more physical RAM or need to reduce your workload.

Process List

The main section displays all running processes with details like:

  • PID (Process ID)
  • User (who owns the process)
  • Priority (PR) and Nice values (NI)
  • Virtual (VIRT), Resident (RES), and Shared (SHR) memory usage
  • CPU% and MEM% (percentage of CPU and memory used)
  • Time (how long the process has been running)
  • Command (what program the process is)

Running and Using Htop

Running htop is simple—just log in to the command line (via SSH or local terminal) and type:

htop

Useful Controls and Features

Htop offers many useful features through function keys:

  • F1: Help
  • F2: Setup (customise the display)
  • F3: Search for a process
  • F4: Filter processes by name
  • F5: Tree view (show parent-child relationships)
  • F6: Sort by a column
  • F7/F8: Decrease/increase process priority (nice value)
  • F9: Kill a process (useful for terminating unresponsive applications)
  • F10: Quit

You can also use traditional keyboard shortcuts like Ctrl+M to sort by memory usage or Ctrl+P to sort by processor usage.

Customising Htop

Using F2, you can access the setup menu to add more charts to the top section—on both left and right sides. Don’t forget to save your new default settings for future sessions.

This customisation allows you to focus on the metrics most relevant to your specific use case, whether that’s network I/O, memory breakdown, or CPU load averages.

Identifying Performance Issues

When diagnosing why your Raspberry Pi is running slowly, look for:

  1. Processes with high CPU usage (near 100% consistently)
  2. High swap usage (indicating memory pressure)
  3. Processes consuming large amounts of memory
  4. Many zombie processes (may indicate underlying issues)

Once you’ve identified problematic processes, you can decide whether to:

  • Kill unnecessary processes
  • Optimise applications
  • Reduce the services running simultaneously
  • Consider a hardware upgrade if possible

Availability on Other Linux Systems

If you use another flavour of Linux, it most likely has htop available as well. On CentOS-based systems, try:

yum install htop

Conclusion

Htop is an invaluable tool for monitoring and managing your Raspberry Pi’s performance. With its intuitive interface and detailed information, you can quickly identify what might be causing your Pi to slow down and take appropriate action to optimise its performance.

Regular monitoring with htop can help you maintain a smoothly running system by identifying issues before they significantly impact performance, making it an essential addition to any Raspberry Pi enthusiast’s toolkit.

Keeping Your Raspberry Pi Install Tidy After Upgrades and Changes

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Whilst Linux in general is very good at being neat and tidy, devices such as the Raspberry Pi, where resources can be much more limited than other computers, can sometimes suffer—usually from lack of space (performance will be dealt with in another post).

The Problem with Updates and Package Changes

If you’ve recently made changes—removed some packages, or manually updated some components—you may find your disk space getting a bit lower. This is because Linux package managers don’t always clean up perfectly after themselves. Some common scenarios that lead to wasted space include:

  • Cached package files that were downloaded during updates
  • Dependencies that are no longer needed after removing applications
  • Older versions of packages kept after upgrades
  • Temporary files created during installations

Simple Cleanup Commands

Fortunately, one of the tools you can use is built into apt-get and allows it to scan and remove dependencies no longer required. To reclaim your disk space, simply run the following commands:

1. Clean Up Package Archives

sudo apt-get autoclean

This removes old archive files that might have been left behind. Note you can use clean as well—however, this can cause slowness as it removes all archive files, and some may be needed again soon if you’re frequently installing and updating packages.

2. Remove Unused Packages

sudo apt-get autoremove

This removes any unused packages—often these can be left behind if you remove a programme which had optional dependencies, as these dependencies are not always removed by the system. Other system changes may have now marked certain packages as unused as well.

Results You Can Expect

The output of these commands will look similar to this:

Screen-Shot-2016-02-03-at-00.37.23 Claiming back some disk space using apt-get autoremove

In this particular example, I gained back 300MB of space. However, I’ve previously recovered as much as 1.2 gigabytes from a Raspberry Pi that had gone through multiple update cycles and application changes.

When to Run These Commands

For optimal system maintenance, consider running these cleanup commands:

  1. After removing large applications
  2. Following significant system updates
  3. When you receive low disk space warnings
  4. As part of a regular monthly maintenance routine
  5. Before creating a backup or disk image

Additional Space-Saving Tips

Beyond these basic commands, here are some other ways to keep your Raspberry Pi’s storage optimised:

Clear Logs

Log files can accumulate over time. To safely truncate them:

sudo journalctl --vacuum-time=7d

This keeps only the last seven days of logs.

Check for Large Files

You can find unexpected space-hogging files with:

sudo find / -type f -size +100M

This will list all files larger than 100MB, helping you identify potential candidates for removal.

Minimise Installed Packages

Consider running a minimal installation if your Raspberry Pi is dedicated to a specific task. Many Raspberry Pi OS installations include software you might not need.

Conclusion

Regular maintenance using these simple commands can help ensure your Raspberry Pi runs efficiently within its storage constraints. This is particularly important for models with smaller SD cards or for projects that generate or download significant amounts of data.

By integrating these cleanup steps into your routine maintenance, you can avoid the frustration of running out of space unexpectedly and extend the useful life of your SD card by reducing unnecessary write cycles.

Wi-Fi for Raspberry Pi: Setting Up the Edimax Nano USB Adapter

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The Raspberry Pi computer comes without Wi-Fi initially, but its true freedom is reached when you connect it wirelessly. There are a number of options for this, but I’d recommend using the Edimax Nano USB adapter. It’s easy to set up your Raspberry Pi to work with this device—just follow this straightforward guide.

Required Hardware

First, you need the Wi-Fi dongle (other adapters may work with this guide, as long as they have drivers for the Raspberry Pi). The Edimax Nano USB adapter is available from Amazon UK and other retailers.

Once you have the dongle, simply plug it directly into one of the Raspberry Pi’s USB ports. I recommend using a direct port rather than connecting via a USB hub, as sometimes problems can occur going through a hub. The Raspberry Pi has enough power to run this compact networking tool without issues.

Verifying the Adapter Is Detected

First, let’s check that your Raspberry Pi recognises the adapter. For convenience, I’ll use sudo su to switch to root access (remember to exit this level when you’re finished):

sudo su

Now, check the USB devices with:

lsusb

You should see your device listed, similar to this:

Screen-Shot-2016-01-19-at-13.09.19

The line with “Edimax” shows your device is detected and you’re ready to configure it.

Checking Current Wi-Fi Status

If you have configured Wi-Fi before (for another adapter), it may have already connected. Type:

iwconfig

If it says “unassociated”, then you need to proceed with configuration. If it’s associated (like the screenshot below), you’re done and don’t need to do anything further:

Screen-Shot-2016-01-19-at-14.34.27

The top line ESSID indicates that the Wi-Fi is configured and working. If you cannot see wlan0 or wlan1, then your device is not working yet—try unplugging it or rebooting your Raspberry Pi.

Configuration Steps: Network Interfaces

First, we need to make sure the WLAN interface is set up for hot-plugging and establish the filepath for the configuration. Edit the network interfaces file:

nano /etc/network/interfaces

Make sure the following lines are present (some are probably already there):

auto wlan0
allow-hotplug wlan0
iface wlan0 inet manual
wpa-roam /etc/wpa_supplicate/wpa_supplicant.conf

If you find a wlan1 entry, you may want to add similar lines for it as well (this sometimes happens if you switch the USB ports). This ensures any wireless interface connects properly (alternatively, you can point to a different configuration file to connect to different networks).

Screen-Shot-2016-01-19-at-23.51.39

Configuration Steps: Wi-Fi Security Details

Now we need to edit the WPA supplicant file and add your network details:

nano /etc/wpa_supplicate/wpa_supplicant.conf

If the fields are missing, add them in. Put your SSID and password in quotes as shown:`

network={
ssid="YOUR SSID HERE"
psk="YOUR KEY HERE"
proto=RSN
key_mgmt=WPA-PSK
pairwise=CCMP TKIP
group=CCMP TKIP
}

Bringing Up the Wi-Fi Interface

Once you’ve completed the configuration, bring up the interface:

ifup wlan0

You may get some errors, but it is usually safe to ignore them. To see if the configuration has worked, run:

ifconfig wlan0

You should see an IP address assigned to the interface:

Troubleshooting

If you encounter any problems, I’d recommend rebooting your Raspberry Pi. This will start up the wireless interface as the system boots.

sudo reboot

After rebooting, check the connection status again with iwconfig to confirm everything is working properly.

Benefits of Wi-Fi on Your Raspberry Pi

Adding wireless connectivity to your Raspberry Pi offers numerous advantages:

  1. Flexibility in placement: Position your Pi anywhere within your Wi-Fi range
  2. Reduced cable clutter: No more trailing Ethernet cables
  3. Portable projects: Ideal for mobile applications and projects
  4. Remote access: Easily SSH into your Pi from anywhere on your network
  5. Internet of Things (IoT) applications: Perfect for connected devices and sensors

Conclusion

The Edimax Nano USB adapter is an excellent, compact choice for adding Wi-Fi capabilities to your Raspberry Pi. Once properly configured, it provides reliable wireless connectivity that opens up new possibilities for your Raspberry Pi projects.

With this small and affordable addition, your Raspberry Pi can be transformed from a tethered computer into a fully mobile computing platform, ready to power your next creative endeavour.

Monitoring Disk Space Usage on Raspberry Pi with ncdu

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You’ve had your Raspberry Pi working away, first as a media center, then a web server with a database, and you’ve been tinkering with lots of other features. But now you’re wondering: what exactly is taking up all your storage space?

Fortunately, when running Raspbian, the Raspberry Pi comes with an excellent command-line tool already installed that makes analyzing disk usage straightforward and intuitive.

Introducing ncdu: NCurses Disk Usage

The ncdu tool (NCurses Disk Usage) provides an interactive, visual way to explore your Raspberry Pi’s storage. It’s significantly more user-friendly than the standard du command and allows you to navigate through your directory structure to find space-hogging files and folders.

Basic Usage

To start using ncdu, simply open a terminal or SSH into your Raspberry Pi and type:

ncdu

This command will scan your current directory and all subdirectories, displaying a sorted list of folders by size.

If you want to analyze a specific location, you can provide a path:

ncdu /home/pi

Scanning Only the Root Filesystem

One particularly useful option is to only scan the root filesystem without crossing into other mounted devices (like external hard drives or network shares). This gives you a clear picture of what’s taking up space on your SD card:

ncdu -x /

The -x flag tells ncdu to stay on one filesystem and not cross filesystem boundaries.

Reading the Display

After scanning, ncdu will show you something like this:

    2.6GiB [##########] /usr
    1.0GiB [###       ] /home
  633.8MiB [##        ] /opt
  593.0MiB [##        ] /var
  141.4MiB [          ] /lib
   10.2MiB [          ] /media
   10.1MiB [          ] /mnt
    7.9MiB [          ] /bin
    7.5MiB [          ] /sbin
    6.7MiB [          ] /etc
    1.7MiB [          ] /tmp
   40.0KiB [          ] /root
   16.0KiB [          ] /lost+found
    4.0KiB [          ] /srv
    0.0  B [          ] /sys
    0.0  B [          ] /run
    0.0  B [          ] /proc
    0.0  B [          ] /dev
    0.0  B [          ] /boot

This visual representation makes it immediately obvious where your space is being used. In this example, the /usr directory is using 2.6GB, while /home is using 1GB.

Navigating the Interface

Once ncdu is displaying the results, you can:

  • Use the arrow keys to move up and down the list
  • Press Enter to dive into a directory
  • Press Backspace or Left arrow to go back to the parent directory
  • Press q to quit the program

This interactive navigation makes it easy to drill down into directories to find exactly what’s consuming your space.

Advanced Features: Exporting Reports

If you want to save your disk usage analysis for later reference or comparison, ncdu allows you to export reports:

ncdu -x -o /home/pi/filesystem.txt /

This command will scan the root filesystem and save the report to /home/pi/filesystem.txt. Note that this file is in a binary format and isn’t human-readable directly.

To view an exported report later:

ncdu -f /home/pi/filesystem.txt

This feature is particularly useful for:

  • Tracking space usage over time
  • Comparing before/after a cleanup operation
  • Documenting system state before making major changes

When to Use This Tool

The ncdu utility is particularly valuable when:

  1. Your Raspberry Pi is running low on space
  2. You’re trying to optimize an SD card with limited capacity
  3. You suspect log files or cache directories might be filling up
  4. You need to identify which applications are consuming the most storage
  5. You’re preparing to back up or clone your system

Conclusion

The ncdu tool provides a user-friendly way to analyse disk usage on your Raspberry Pi. Instead of guessing what might be taking up space or running multiple commands to piece together the information, this single utility gives you a clear, interactive view of your storage situation.

If you’re managing a Raspberry Pi for any length of time, this tool will likely become an essential part of your maintenance routine. Give it a try next time you’re wondering where all your free space has gone!

Copyright Michael Helm 2026.
The earliest version of this site available is from October 2003 - possibly viewable here: https://web.archive.org/web/20031228013629/http://www.ihelm.org.uk:80/

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