delete_module(2) — Linux manual page


delete_module(2)           System Calls Manual          delete_module(2)

NAME         top

       delete_module - unload a kernel module

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <fcntl.h>            /* Definition of O_* constants */
       #include <sys/syscall.h>      /* Definition of SYS_* constants */
       #include <unistd.h>

       int syscall(SYS_delete_module, const char *name, unsigned int flags);

       Note: glibc provides no wrapper for delete_module(),
       necessitating the use of syscall(2).

DESCRIPTION         top

       The delete_module() system call attempts to remove the unused
       loadable module entry identified by name.  If the module has an
       exit function, then that function is executed before unloading
       the module.  The flags argument is used to modify the behavior of
       the system call, as described below.  This system call requires

       Module removal is attempted according to the following rules:

       (1)  If there are other loaded modules that depend on (i.e.,
            refer to symbols defined in) this module, then the call

       (2)  Otherwise, if the reference count for the module (i.e., the
            number of processes currently using the module) is zero,
            then the module is immediately unloaded.

       (3)  If a module has a nonzero reference count, then the behavior
            depends on the bits set in flags.  In normal usage (see
            NOTES), the O_NONBLOCK flag is always specified, and the
            O_TRUNC flag may additionally be specified.

            The various combinations for flags have the following

            flags == O_NONBLOCK
                   The call returns immediately, with an error.

            flags == (O_NONBLOCK | O_TRUNC)
                   The module is unloaded immediately, regardless of
                   whether it has a nonzero reference count.

            (flags & O_NONBLOCK) == 0
                   If flags does not specify O_NONBLOCK, the following
                   steps occur:

                   •  The module is marked so that no new references are

                   •  If the module's reference count is nonzero, the
                      caller is placed in an uninterruptible sleep state
                      (TASK_UNINTERRUPTIBLE) until the reference count
                      is zero, at which point the call unblocks.

                   •  The module is unloaded in the usual way.

       The O_TRUNC flag has one further effect on the rules described
       above.  By default, if a module has an init function but no exit
       function, then an attempt to remove the module fails.  However,
       if O_TRUNC was specified, this requirement is bypassed.

       Using the O_TRUNC flag is dangerous!  If the kernel was not built
       with CONFIG_MODULE_FORCE_UNLOAD, this flag is silently ignored.
       (Normally, CONFIG_MODULE_FORCE_UNLOAD is enabled.)  Using this
       flag taints the kernel (TAINT_FORCED_RMMOD).

RETURN VALUE         top

       On success, zero is returned.  On error, -1 is returned and errno
       is set to indicate the error.

ERRORS         top

       EBUSY  The module is not "live" (i.e., it is still being
              initialized or is already marked for removal); or, the
              module has an init function but has no exit function, and
              O_TRUNC was not specified in flags.

       EFAULT name refers to a location outside the process's accessible
              address space.

       ENOENT No module by that name exists.

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

              Other modules depend on this module; or, O_NONBLOCK was
              specified in flags, but the reference count of this module
              is nonzero and O_TRUNC was not specified in flags.

STANDARDS         top


HISTORY         top

       The delete_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 system call took only one argument:

          int delete_module(const char *name);

       If name is NULL, all unused modules marked auto-clean are

       Some further details of differences in the behavior of
       delete_module() in Linux 2.4 and earlier are not currently
       explained in this manual page.

NOTES         top

       The uninterruptible sleep that may occur if O_NONBLOCK is omitted
       from flags is considered undesirable, because the sleeping
       process is left in an unkillable state.  As at Linux 3.7,
       specifying O_NONBLOCK is optional, but in future kernels it is
       likely to become mandatory.

SEE ALSO         top

       create_module(2), init_module(2), query_module(2), lsmod(8),
       modprobe(8), rmmod(8)

COLOPHON         top

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Linux man-pages 6.9.1          2024-05-02               delete_module(2)

Pages that refer to this page: create_module(2)get_kernel_syms(2)init_module(2)query_module(2)syscalls(2)unimplemented(2)systemd.exec(5)capabilities(7)