lsmod Command Linux: Complete Guide to Listing Kernel Modules

The lsmod command is an essential Linux utility that displays information about currently loaded kernel modules in your system. Understanding how to use this command effectively is crucial for system administrators, developers, and anyone working with Linux kernel management.

What is the lsmod Command?

The lsmod command stands for “list modules” and provides a formatted view of the kernel modules currently loaded in memory. It reads information from the /proc/modules file and presents it in a user-friendly format showing module names, sizes, usage counts, and dependencies.

Basic Syntax and Usage

The basic syntax of the lsmod command is straightforward:

lsmod [options]

In most cases, you’ll use lsmod without any options:

lsmod

Sample Output Explanation

When you run lsmod, you’ll see output similar to this:

Module                  Size  Used by
nvidia_drm             69632  4
nvidia_modeset       1142784  10 nvidia_drm
nvidia              35282944  412 nvidia_modeset
bluetooth             737280  31 btusb,bnep,btrtl,btbcm,btintel
rfkill                 32768  9 bluetooth,cfg80211
snd_hda_codec_hdmi     73728  1
snd_hda_intel          57344  5
snd_intel_dspcfg       32768  2 snd_hda_intel,snd_sof_intel_hda_common

This output contains three columns:

• Module: The name of the loaded kernel module
• Size: Memory size occupied by the module in bytes
• Used by: Shows the usage count and which modules depend on this module

Understanding Module Dependencies

The “Used by” column reveals important dependency relationships between modules. For example, in the output above:

• nvidia is used by 412 processes and the nvidia_modeset module
• bluetooth is used by multiple modules: btusb, bnep, btrtl, btbcm, and btintel

Command Options and Variations

Basic lsmod Command

lsmod

This displays all currently loaded modules with their basic information.

Filtering Output with grep

To find specific modules, combine lsmod with grep:

# Find audio-related modules
lsmod | grep snd

# Find network-related modules
lsmod | grep net

# Find USB-related modules
lsmod | grep usb

Sorting Output by Size

To see modules sorted by memory usage:

# Sort by size (largest first)
lsmod | sort -k2 -nr

# Sort by size (smallest first)
lsmod | sort -k2 -n

Practical Examples and Use Cases

Example 1: Checking Graphics Driver Modules

$ lsmod | grep -i nvidia
nvidia_drm             69632  4
nvidia_modeset       1142784  10 nvidia_drm
nvidia              35282944  412 nvidia_modeset

This shows all NVIDIA-related modules and their dependencies, useful for troubleshooting graphics issues.

Example 2: Monitoring USB Modules

$ lsmod | grep usb
usbhid                 57344  0
hid                   147456  2 usbhid,hid_generic
usb_storage            81920  1
usbcore               299008  6 usbhid,usb_storage,btusb,xhci_hcd,xhci_pci

This helps identify USB-related kernel modules when diagnosing USB device issues.

Example 3: Finding the Largest Modules

$ lsmod | head -1; lsmod | sort -k2 -nr | head -10
Module                  Size  Used by
nvidia              35282944  412 nvidia_modeset
i915                 2093056  12
xfs                  1540096  1
libcrc32c              16384  4 nf_conntrack,nf_nat,xfs,raid456

This shows the largest modules by memory consumption, helpful for memory optimization.

Alternative Ways to View Module Information

Using /proc/modules Directly

cat /proc/modules | head -5

This shows the raw module information that lsmod formats.

Using modinfo for Detailed Module Information

# Get detailed information about a specific module
modinfo nvidia

# Get just the description
modinfo -d nvidia

Troubleshooting with lsmod

Identifying Missing Modules

When hardware isn’t working, check if required modules are loaded:

# Check for Wi-Fi modules
lsmod | grep -i wifi
lsmod | grep -i wlan

# Check for sound modules
lsmod | grep -i snd
lsmod | grep -i audio

Finding Module Conflicts

Sometimes modules conflict with each other. Use lsmod to identify loaded modules before troubleshooting:

# Save current module list
lsmod > /tmp/modules_before.txt

# After making changes, compare
lsmod > /tmp/modules_after.txt
diff /tmp/modules_before.txt /tmp/modules_after.txt

Security Considerations

The lsmod command is generally safe to use and doesn’t require root privileges. However, the information it provides can be valuable for system reconnaissance, so consider this in security-sensitive environments.

Related Commands

Several other commands work alongside lsmod for module management:

• modprobe: Load and unload kernel modules
• insmod: Insert a module into the kernel
• rmmod: Remove a module from the kernel
• modinfo: Show information about a kernel module
• depmod: Generate module dependency information

Performance Impact and Best Practices

The lsmod command has minimal performance impact as it simply reads from the /proc filesystem. Here are some best practices:

• Use lsmod regularly to monitor system state
• Combine with other commands for comprehensive module management
• Save module lists before system changes for comparison
• Use filtering to focus on specific module categories

Common Error Scenarios

While lsmod rarely fails, you might encounter these situations:

• Permission denied: Usually not an issue with lsmod, but related module management commands may require root access
• Empty output: Indicates no modules are loaded (rare in modern systems)
• Module not found: When filtering, no modules match your criteria

Conclusion

The lsmod command is a fundamental tool for Linux system administration and troubleshooting. By understanding how to use it effectively, you can better manage your system’s kernel modules, diagnose hardware issues, and optimize system performance. Whether you’re a system administrator, developer, or Linux enthusiast, mastering lsmod will enhance your ability to work with the Linux kernel effectively.

Remember that lsmod provides a snapshot of your system’s current state, and module loading can change based on hardware detection, system boot, and manual intervention. Regular monitoring with lsmod helps maintain awareness of your system’s kernel module status and can be invaluable for troubleshooting and optimization tasks.