/proc/modules: Explanation & Insights

Lists the kernel modules that are currently loaded on the system

The file /proc/modules is a representation of the state of the kernel's module loader at a particular point in time. It provides a snapshot of all modules that are currently loaded into the Kernel.

What does /proc/modules contain?

The /proc/modules file contains several pieces of information about each loaded module, including:

The module name
The size of the module (in bytes)
The number of instances of the module currently loaded
The state of the module (Live, Loading, Unloading)
The list of modules that this module depends on
The memory addresses where the module is loaded

Here is an example of what you might see in a /proc/modules file:

nf_conntrack 139264 9 nf_conntrack_ipv6,iptable_nat,nf_nat,nf_nat_ipv4,nf_nat_ipv6,xt_conntrack,nf_conntrack_ipv4,nf_conntrack_ipv6,Live 0xffffffffc0a6a000
ip_tables 24576 1 iptable_nat,Live 0xffffffffc0a62000
x_tables 40960 10 xt_conntrack,iptable_nat,ip_tables,Live 0xffffffffc0a58000

Why is /proc/modules important?

Understanding the /proc/modules file can prove crucial in several situations. For example, if your system is experiencing a high load or other performance issues, you might be able to trace the problem to a specific module by looking at this file. Additionally, if you're trying to load a module and it's failing, the /proc/modules file might provide insight into why.

How to use /proc/modules?

The /proc/modules file can be simply read using the cat command. For example:

cat /proc/modules

You can also use the grep command to search for a specific module:

grep 'module_name' /proc/modules

Common problems related to /proc/modules

One common problem is having a module that is stuck in the 'Loading' or 'Unloading' state. If a module is in this state for a long time, it could be causing a performance issue.

Another typical problem is a module failing to load due to a dependency on another module that isn't loaded. In this case, /proc/modules can help you identify the missing dependency.

Conclusion

In this post, we've explored the /proc/modules file - an important file in Linux that contains valuable information about the currently loaded modules in the kernel. Understanding this file can greatly assist system administrators in diagnosing and solving performance issues.