Software & Apps Linux All About the Linux/Unix Command depmod Make sure the correct modules are always loaded on Linux By Juergen Haas Writer Former Lifewire writer Juergen Haas is a software developer, data scientist, and a fan of the Linux operating system. our editorial process Juergen Haas Updated February 19, 2020 Linux Switching from Windows Tweet Share Email Depmod handles dependency descriptions for loadable kernel modules. Synopsis depmod [-aA] [-ehnqrsuvV] [-C configfile] [-F kernelsyms] [-b basedirectory] [forced_version] depmod [-enqrsuv] [-F kernelsyms] module1.o module2.o ... Description The depmod and modprobe utilities are intended to make a Linux modular kernel manageable for all users, administrators, and distribution maintainers. Depmod creates a "Makefile"-like dependency file, based on the symbols it finds in the set of modules mentioned on the command line or from the directories specified in the configuration file. This dependency file is later used by modprobe to automatically load the correct module or stack of modules. The normal use of depmod is to include the line /sbin/depmod -a somewhere in the rc-files in /etc/rc.d, so that the correct module dependencies will be available immediately after booting the system. If you're working with a more feature complete distribution, like Ubuntu, Debian, or Fedora, this will be done for you. Note that the option -a is now optional. For boot-up purposes, the option -q might be more appropriate since that makes depmod silent about unresolved symbols. If you want to see exactly what's being added, use the -v switch to run the command verbosely. It is also possible to create the dependency file immediately after compiling a new kernel. If you do "depmod -a 2.2.99" when you have compiled kernel 2.2.99 and its modules the first time, while still running e.g. 2.2.98, the file will be created in the correct place. In this case, however, the dependencies on the kernel will not be guaranteed to be correct. See the options -F, -C and -b above for more information on handling this. While building the relationship between modules and the symbols exported by other modules,depmod does not consider the GPL status of the modules nor of the exported symbols. That is, depmod will not flag an error if a module without a GPL compatible license refers to a GPL only symbol (EXPORT_SYMBOL_GPL in the kernel). However, insmod will refuse to resolve GPL only symbols for non-GPL modules so the actual load will fail. Options -a, --all Search for modules in all directories specified in the (optional) configuration file/etc/modules.conf. -A, --quick Compare file timestamps and, if necessary, act like depmod -a. This option only updates the dependency file if anything has changed. -e, --errsyms Show all the unresolved symbols for each module. -h, --help Display a summary of options and immediately exit. -n, --show Write the dependency file on stdout instead of in the /lib/modules tree. -q, --quiet Tell depmod to keep quiet and not to complain about missing symbols. -r, --root Some users compile modules under a non-root userid, then install the modules as root. This process can leave the modules owned by the non-root userid, even though the modules directory is owned by root. If the non-root userid is compromised, an intruder can overwrite existing modules owned by that userid and use this exposure to bootstrap up to root access. By default, modutils will reject attempts to use a module that is not owned by root. Specifying-r will suppress the error and allow root to load modules that are not owned by root. Use of -r is a major security exposure and is not recommended. -s, --syslog Write all error messages via the syslog daemon instead of stderr. -u, --unresolved-error depmod 2.4 does not set a return code when there are any unresolved symbols. Some distributions want a non-zero return code in modutils 2.4 but that change might cause problems for users who expect the old behavior. If you want a non-zero return code in depmod 2.4, specify -u. depmod 2.5 will silently ignore the -u flag and will always give a non-zero return code for unresolved symbols. -v, --verbose Show the name of each module as it is being processed. -V, --version Display the version of depmod. Managing Distributions The following options are useful for people managing distributions: -b basedirectory, --basedir basedirectory If the directory tree /lib/modules containing the sub-trees of modules is moved somewhere else in order to handle modules for a different environment, the -b option tells depmod where to find the moved image of the /lib/modules tree. The file references in the depmod output file that is built, modules.dep, will not contain the basedirectory path. This means that when the file tree is moved back from basedirectory/lib/modules into /lib/modules in the final distribution, all references will be correct. -C configfile, --config configfile Use the file configfile instead of /etc/modules.conf. The environment variable MODULECONF can also be used to select a different configuration file from the default /etc/modules.conf (or/etc/conf.modules (deprecated)). When environment variable UNAME_MACHINE is set, modutils will use its value instead of the machine field from the uname() syscall. This is mainly of use when you are compiling 64 bit modules in 32 bit userspace or vice versa, set UNAME_MACHINE to the type of the modules being built. Current modutils does not support full cross build mode for modules, it is limited to choosing between 32 and 64 bit versions of the host architecture. -F kernelsyms,--filesyms kernelsyms When building dependency files for a different kernel than the currently running kernel, it is important that depmod uses the correct set of kernel symbols to resolve the kernel references in each module. These symbols can either be a copy of System.map from the other kernel or a copy of the output from /proc/ksyms. If your kernel uses versioned symbols, it is best to use a copy of the /proc/ksyms output, since that file contains the symbol versions of the kernel symbols. However, you can use a System.map even with versioned symbols. Configuration The behavior of depmod and modprobe can be adjusted by the (optional) configuration file/etc/modules.conf. See modprobe(8) and modules.conf(5) for a complete description. Strategy Each time you compile a new kernel, the command "make modules_install" will create a new directory, but won't change the default. When you get a module unrelated to the kernel distribution, you should place it in one of the version-independent directories under /lib/modules. This is the default strategy, which can be overridden in /etc/modules.conf. Use the man command (% man) to see how a command is used on your particular computer.