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.TH DELETE_MODULE 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

delete_module \- unload a kernel module

.SH SYNOPSIS

.nf

.BI "int delete_module(const char *" name ", int " flags );

.fi

.PP

.IR Note :

No declaration of this system call is provided in glibc headers; see NOTES.

.SH DESCRIPTION

The

.BR delete_module ()

system call attempts to remove the unused loadable module entry

identified by

.IR name .

If the module has an

.I exit

function, then that function is executed before unloading the module.

The

.IR flags

argument is used to modify the behavior of the system call,

as described below.

This system call requires privilege.

.PP

Module removal is attempted according to the following rules:

.IP 1. 4

If there are other loaded modules that depend on

(i.e., refer to symbols defined in) this module,

then the call fails.

.IP 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.

.IP 3.

If a module has a nonzero reference count,

then the behavior depends on the bits set in

.IR flags .

In normal usage (see NOTES), the

.BR O_NONBLOCK

flag is always specified, and the

.BR O_TRUNC

flag may additionally be specified.

.\"  	O_TRUNC == KMOD_REMOVE_FORCE in kmod library

.\"  	O_NONBLOCK == KMOD_REMOVE_NOWAIT in kmod library

.IP

The various combinations for

.I flags

have the following effect:

.RS 4

.TP

.B flags == O_NONBLOCK

The call returns immediately, with an error.

.TP

.B flags == (O_NONBLOCK | O_TRUNC)

The module is unloaded immediately,

regardless of whether it has a nonzero reference count.

.TP

.B (flags & O_NONBLOCK) == 0

If

.I flags

does not specify

.BR O_NONBLOCK ,

the following steps occur:

.RS

.IP * 3

The module is marked so that no new references are permitted.

.IP *

If the module's reference count is nonzero,

the caller is placed in an uninterruptible sleep state

.RB ( TASK_UNINTERRUPTIBLE )

until the reference count is zero, at which point the call unblocks.

.IP *

The module is unloaded in the usual way.

.RE

.RE

.PP

The

.B O_TRUNC

flag has one further effect on the rules described above.

By default, if a module has an

.I init

function but no

.I exit

function, then an attempt to remove the module fails.

However, if

.BR O_TRUNC

was specified, this requirement is bypassed.

.PP

Using the

.B O_TRUNC

flag is dangerous!

If the kernel was not built with

.BR CONFIG_MODULE_FORCE_UNLOAD ,

this flag is silently ignored.

(Normally,

.BR CONFIG_MODULE_FORCE_UNLOAD

is enabled.)

Using this flag taints the kernel (TAINT_FORCED_RMMOD).

.SH RETURN VALUE

On success, zero is returned.

On error, \-1 is returned and

.I errno

is set appropriately.

.SH ERRORS

.TP

.B EBUSY

The module is not "live"

(i.e., it is still being initialized or is already marked for removal);

or, the module has

an

.I init

function but has no

.I exit

function, and

.B O_TRUNC

was not specified in

.IR flags .

.TP

.B EFAULT

.I name

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

.TP

.B ENOENT

No module by that name exists.

.TP

.B EPERM

The caller was not privileged

(did not have the

.B CAP_SYS_MODULE

capability),

or module unloading is disabled

(see

.IR /proc/sys/kernel/modules_disabled

in

.BR proc (5)).

.TP

.B EWOULDBLOCK

Other modules depend on this module;

or,

.BR O_NONBLOCK

was specified in

.IR flags ,

but the reference count of this module is nonzero and

.B O_TRUNC

was not specified in

.IR flags .

.SH CONFORMING TO

.BR delete_module ()

is Linux-specific.

.SH NOTES

The

.BR 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 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

.BR syscall (2).

.PP

The uninterruptible sleep that may occur if

.BR O_NONBLOCK

is omitted from

.IR flags

is considered undesirable, because the sleeping process is left

in an unkillable state.

As at Linux 3.7, specifying

.BR O_NONBLOCK

is optional, but in future kernels it is likely to become mandatory.

.SS Linux 2.4 and earlier

In Linux 2.4 and earlier, the system call took only one argument:

.PP

.BI "   int delete_module(const char *" name );

.PP

If

.I name

is NULL, all unused modules marked auto-clean are removed.

.PP

Some further details of differences in the behavior of

.BR delete_module ()

in Linux 2.4 and earlier are

.I not

currently explained in this manual page.

.SH SEE ALSO

.BR create_module (2),

.BR init_module (2),

.BR query_module (2),

.BR lsmod (8),

.BR modprobe (8),

.BR rmmod (8)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.