Compiling kernal vs modprobe -i / -r

[jsmaye]

As I understand it, a general-purpose non-customized kernal has a collection of (for lack of a better word) modules compiled into it that are what someone has determined to be generic and all-purpose. What is later needed but not in the compilation is run as external (to the kernal) services. Some people re-compile their kernals to include what they use and exclude what they don't. I'm guessing that things that run in the kernal are faster and/or take up less space or fewer resources, and things in the kernal that are not needed are wasted space and resource. I thought about eventually learning how to recompile a kernal, but aside from the experience of doing it, is there that much of a gain?

Second question - how does using modprobe to install or remove modules compare to re-compiling a kernal? Is it permanent? For instance, let's say my kernal has appletalk in it. Do I gain anything by removing it? Can I even remove it (man is a little fuzzy about whether you can even use modprobe to remove modules)?

[alacheesu]

I read a post that you might find interesting.

http://www.fedoraforum.org/forum/showthread.php?t=18627

Hope this helps.

[jsmaye]

Outstanding article - I had no idea the kernal was already 99% optimized out of the box.

Now, what exaclty does modprobe do, and is it permanent, or must it be done after every boot?

[james_in_denver]

Modprobe is not permament, it's run at every system boot........

The difference is that with "modprobe" you can specify certain paramters and actions for modules BEFORE they are loaded, like IRQ, shared memory, etc.......

[AndyGreen]

modprobe adds the code and data in to module to the kernel running in memory in realtime. It therefore only persists until the next reboot when the kernel without any modules is loaded into RAM fresh.

A little more info: modules have dependencies just like RPMs. If you do, for example

modinfo usb-storage

and scroll back, you'll see

Depends: scsi_mod

which is another module that implements the SCSI command set. When you build a kernel or you compile a new module, a utilty

depmod

is run which goes though all the modules making a database of who needs what. The command

insmod modulename

inserts just the module into the kernel without dependencies, so if other modules are needed that are not already loaded in you will get an error;

modprobe modulename

loads in both the given module AND any modules it is depenedent on. So modprobe is like the "yum of modules".