depmod analyzes your kernel modules (in the directory /lib/modules/kernel-release) and creates a list of dependencies (named modules.dep), so that when modules are added and removed with modprobe, no modules are without the other modules they require. At the same time, it creates a map correlating hardware identifiers and the modules that handle them. This mapping is used to find the correct module when a piece of hardware requests it.

The kernel relies on depmod and modprobe to pass it the raw data for its modules, in the order it needs to load them.

depmod [-b basedir] [-e] [-E Module.symvers] [-F System.map]
       [-n] [-v] [-A] [-P prefix] [-w] [version]

depmod [-e] [-E Module.symvers] [-F System.map] [-m] [-n] [-v] [-P prefix]
       [-w] [version] [filename...]

Technical Description

Linux kernel modules can provide services (called "symbols") for other modules to use (using one of the EXPORT_SYMBOL variants in the code). If a second module uses this symbol, that second module clearly depends on the first module. These dependencies can get quite complex.

depmod creates a list of module dependencies by reading each module under /lib/modules/kernel-release and determining what symbols it exports and what symbols it needs. By default, this list is written to modules.dep, and a binary hashed version named modules.dep.bin, in the same directory. If file names are given on the command line, only those modules are examined (which is rarely useful unless all modules are listed).

depmod also creates a list of symbols provided by modules in the file named modules.symbols and its binary hashed version, modules.symbols.bin.

Finally, depmod will output a file named modules.devname if modules supply special device names (devname) that should be populated in /dev on boot (by a utility such as udev).

If a version is provided, then that kernel version's module directory is used rather than the current kernel version (as returned by uname -r).

Options

The following series of commands illustrate a common way to use depmod. Each command is prefixed with sudo, since they require root permissions:

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

sudo depmod -a

sudo modprobe your-kernel-module

These commands perform the following operations:

1. In the first command, we use ln to create a symbolic link to our module file in the directory /lib/modules/kernel-release. The command uname -r, enclosed in back quotes, is executed by the shell and translates to the appropriate string representing our kernel release version.
2. In the second command, an updated dependency list is generated by depmod -a to make sure that the module we're installing is aware of all existing modules and dependencies. This dependency list will be used by modprobe when installing the module in the third command.
3. modprobe installs the kernel module.