finit_module(2) — Linux manual page


INIT_MODULE(2)            Linux Programmer's Manual           INIT_MODULE(2)

NAME         top

       init_module, finit_module - load a kernel module

SYNOPSIS         top

       int init_module(void *module_image, unsigned long len,
                       const char *param_values);

       int finit_module(int fd, const char *param_values,
                        int flags);

       Note: glibc provides no header file declaration of init_module() and
       no wrapper function for finit_module(); see NOTES.

DESCRIPTION         top

       init_module() loads an ELF image into kernel space, performs any
       necessary symbol relocations, initializes module parameters to values
       provided by the caller, and then runs the module's init function.
       This system call requires privilege.

       The module_image argument points to a buffer containing the binary
       image to be loaded; len specifies the size of that buffer.  The
       module image should be a valid ELF image, built for the running

       The param_values argument is a string containing space-delimited
       specifications of the values for module parameters (defined inside
       the module using module_param() and module_param_array()).  The
       kernel parses this string and initializes the specified parameters.
       Each of the parameter specifications has the form:


       The parameter name is one of those defined within the module using
       module_param() (see the Linux kernel source file
       include/linux/moduleparam.h).  The parameter value is optional in the
       case of bool and invbool parameters.  Values for array parameters are
       specified as a comma-separated list.

       The finit_module() system call is like init_module(), but reads the
       module to be loaded from the file descriptor fd.  It is useful when
       the authenticity of a kernel module can be determined from its
       location in the filesystem; in cases where that is possible, the
       overhead of using cryptographically signed modules to determine the
       authenticity of a module can be avoided.  The param_values argument
       is as for init_module().

       The flags argument modifies the operation of finit_module().  It is a
       bit mask value created by ORing together zero or more of the
       following flags:

              Ignore symbol version hashes.

              Ignore kernel version magic.

       There are some safety checks built into a module to ensure that it
       matches the kernel against which it is loaded.  These checks are
       recorded when the module is built and verified when the module is
       loaded.  First, the module records a "vermagic" string containing the
       kernel version number and prominent features (such as the CPU type).
       Second, if the module was built with the CONFIG_MODVERSIONS
       configuration option enabled, a version hash is recorded for each
       symbol the module uses.  This hash is based on the types of the
       arguments and return value for the function named by the symbol.  In
       this case, the kernel version number within the "vermagic" string is
       ignored, as the symbol version hashes are assumed to be sufficiently

       Using the MODULE_INIT_IGNORE_VERMAGIC flag indicates that the
       "vermagic" string is to be ignored, and the
       MODULE_INIT_IGNORE_MODVERSIONS flag indicates that the symbol version
       hashes are to be ignored.  If the kernel is built to permit forced
       loading (i.e., configured with CONFIG_MODULE_FORCE_LOAD), then
       loading continues, otherwise it fails with the error ENOEXEC as
       expected for malformed modules.

RETURN VALUE         top

       On success, these system calls return 0.  On error, -1 is returned
       and errno is set appropriately.

ERRORS         top

       EBADMSG (since Linux 3.7)
              Module signature is misformatted.

       EBUSY  Timeout while trying to resolve a symbol reference by this

       EFAULT An address argument referred to a location that is outside the
              process's accessible address space.

       ENOKEY (since Linux 3.7)
              Module signature is invalid or the kernel does not have a key
              for this module.  This error is returned only if the kernel
              was configured with CONFIG_MODULE_SIG_FORCE; if the kernel was
              not configured with this option, then an invalid or unsigned
              module simply taints the kernel.

       ENOMEM Out of memory.

       EPERM  The caller was not privileged (did not have the CAP_SYS_MODULE
              capability), or module loading is disabled (see
              /proc/sys/kernel/modules_disabled in proc(5)).

       The following errors may additionally occur for init_module():

       EEXIST A module with this name is already loaded.

       EINVAL param_values is invalid, or some part of the ELF image in
              module_image contains inconsistencies.

              The binary image supplied in module_image is not an ELF image,
              or is an ELF image that is invalid or for a different

       The following errors may additionally occur for finit_module():

       EBADF  The file referred to by fd is not opened for reading.

       EFBIG  The file referred to by fd is too large.

       EINVAL flags is invalid.

              fd does not refer to an open file.

       In addition to the above errors, if the module's init function is
       executed and returns an error, then init_module() or finit_module()
       fails and errno is set to the value returned by the init function.

VERSIONS         top

       finit_module() is available since Linux 3.8.

CONFORMING TO         top

       init_module() and finit_module() are Linux-specific.

NOTES         top

       The init_module() system call is not supported by glibc.  No
       declaration is provided in glibc headers, but, through a quirk of
       history, glibc versions before 2.23 did export an ABI for this system
       call.  Therefore, in order to employ this system call, it is (before
       glibc 2.23) sufficient to manually declare the interface in your
       code; alternatively, you can invoke the system call using syscall(2).

       Glibc does not provide a wrapper for finit_module(); call it using

       Information about currently loaded modules can be found in
       /proc/modules and in the file trees under the per-module
       subdirectories under /sys/module.

       See the Linux kernel source file include/linux/module.h for some
       useful background information.

   Linux 2.4 and earlier
       In Linux 2.4 and earlier, the init_module() system call was rather

           #include <linux/module.h>

           int init_module(const char *name, struct module *image);

       (User-space applications can detect which version of init_module() is
       available by calling query_module(); the latter call fails with the
       error ENOSYS on Linux 2.6 and later.)

       The older version of the system call loads the relocated module image
       pointed to by image into kernel space and runs the module's init
       function.  The caller is responsible for providing the relocated
       image (since Linux 2.6, the init_module() system call does the

       The module image begins with a module structure and is followed by
       code and data as appropriate.  Since Linux 2.2, the module structure
       is defined as follows:

           struct module {
               unsigned long         size_of_struct;
               struct module        *next;
               const char           *name;
               unsigned long         size;
               long                  usecount;
               unsigned long         flags;
               unsigned int          nsyms;
               unsigned int          ndeps;
               struct module_symbol *syms;
               struct module_ref    *deps;
               struct module_ref    *refs;
               int                 (*init)(void);
               void                (*cleanup)(void);
               const struct exception_table_entry *ex_table_start;
               const struct exception_table_entry *ex_table_end;
           #ifdef __alpha__
               unsigned long gp;

       All of the pointer fields, with the exception of next and refs, are
       expected to point within the module body and be initialized as appro‐
       priate for kernel space, that is, relocated with the rest of the mod‐

SEE ALSO         top

       create_module(2), delete_module(2), query_module(2), lsmod(8),

COLOPHON         top

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2017-09-15                   INIT_MODULE(2)

Pages that refer to this page: syscalls(2)