Modprobe vs insmod

What is the differences between modprobe and insmod can be somewhat confusing. I know that modprobe and insmod are used to install  or load modules to linux kernel, but then what are the differences?  Even more, when I tried the following

modprobe /path/to/module.ko

it didn’t work, while when I used

insmod /path/to/module.ko

it worked like a charm.

It turned out to be simple, here are the key points:

1. modprobe calculates all of the module dependencies and then load the module along with the dependencies, while insmod does not care about dependencies, insmod only loads the module in question.

2. How modprobe calculates module dependencies? First let me introduce you the depmod tool, this tool’s function is to calculate module dependencies for all modules located in/lib/modules/`uname -r`/ and then keep the dependencies information in/lib/modules/`uname -r`/modules.dep. depmod usually runs when system is booted or when there is new module installed or when you call depmod -a from shell. For example, consider module A, and this module depends on module B and module C.  depmod finds that module A needs module B and module C, and then depmod keeps this information in form of “A:B C” in/lib/modules/`uname -r`/modules.dep. Now, let us return to modprobe. modprobe basically reads the modules.dep file and then loads, using insmod, the module and all of the dependencies.

3. So why modprobe /path/to/module.ko didn’t work? It is simply because modprobe only deals with modules in /lib/modules/`uname -r`/.  So, if you want it to work, create soft link from/path/to/module.ko to /lib/modules/`uname -r`/.

ln -s /path/to/module.ko /lib/modules/`uname -r`

and don’t forget to refresh the modules.dep

depmod -a

and call the modprobe, also loose the .ko

modprobe module