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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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init_module(2) System Calls Manual init_module(2)
init_module, finit_module - load a kernel module
Standard C library (libc, -lc)
#include <linux/module.h> /* Definition of MODULE_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <unistd.h>
int syscall(unsigned long size;
SYS_init_module, void module_image[size], unsigned long size,
const char *param_values);
int syscall(SYS_finit_module, int fd,
const char *param_values, int flags);
Note: glibc provides no wrappers for these system calls,
necessitating the use of syscall(2).
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; size specifies the size of that buffer. The
module image should be a valid ELF image, built for the running
kernel.
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:
name[=value[,value...]]
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.
finit_module()
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:
MODULE_INIT_IGNORE_MODVERSIONS
Ignore symbol version hashes.
MODULE_INIT_IGNORE_VERMAGIC
Ignore kernel version magic.
MODULE_INIT_COMPRESSED_FILE (since Linux 5.17)
Use in-kernel module decompression.
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 reliable.
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.
If the kernel was build with CONFIG_MODULE_DECOMPRESS, the in-
kernel decompression feature can be used. User-space code can
check if the kernel supports decompression by reading the
/sys/module/compression attribute. If the kernel supports
decompression, the compressed file can directly be passed to
finit_module() using the MODULE_INIT_COMPRESSED_FILE flag. The
in-kernel module decompressor supports the following compression
algorithms:
• gzip (since Linux 5.17)
• xz (since Linux 5.17)
• zstd (since Linux 6.2)
The kernel only implements a single decompression method. This is
selected during module generation accordingly to the compression
method chosen in the kernel configuration.
On success, these system calls return 0. On error, -1 is returned
and errno is set to indicate the error.
EBADMSG (since Linux 3.7)
Module signature is misformatted.
EBUSY Timeout while trying to resolve a symbol reference by this
module.
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.
ENOEXEC
The binary image supplied in module_image is not an ELF
image, or is an ELF image that is invalid or for a
different architecture.
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.
EINVAL The decompressor sanity checks failed, while loading a
compressed module with flag MODULE_INIT_COMPRESSED_FILE
set.
ENOEXEC
fd does not refer to an open file.
EOPNOTSUPP (since Linux 5.17)
The flag MODULE_INIT_COMPRESSED_FILE is set to load a
compressed module, and the kernel was built without
CONFIG_MODULE_DECOMPRESS.
ETXTBSY (since Linux 4.7)
The file referred to by fd is opened for read-write.
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.
Linux.
finit_module()
Linux 3.8.
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 glibc 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).
Linux 2.4 and earlier
In Linux 2.4 and earlier, the init_module() system call was rather
different:
#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 relocation).
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;
typeof(int (void)) *init;
typeof(void (void)) *cleanup;
const struct exception_table_entry *ex_table_start;
const struct exception_table_entry *ex_table_end;
#ifdef __alpha__
unsigned long gp;
#endif
};
All of the pointer fields, with the exception of next and refs,
are expected to point within the module body and be initialized as
appropriate for kernel space, that is, relocated with the rest of
the module.
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.
create_module(2), delete_module(2), query_module(2), lsmod(8),
modprobe(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-06-28 init_module(2)
Pages that refer to this page: create_module(2), delete_module(2), get_kernel_syms(2), query_module(2), syscalls(2), unimplemented(2), systemd.exec(5), capabilities(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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