---
name: "mprotect"
section: "3p"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/mprotect/3p"
---

# mprotect(3p)

set protection of memory mapping

## PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

## NAME

mprotect — set protection of memory mapping

## SYNOPSIS

```
#include <sys/mman.h>
```

int mprotect(void \**addr*, size\_t *len*, int *prot*);

## DESCRIPTION

The *mprotect*() function shall change the access protections to be that specified by *prot* for those whole pages containing any part of the address space of the process starting at address *addr* and continuing for *len* bytes. The parameter *prot* determines whether read, write, execute, or some combination of accesses are permitted to the data being mapped. The *prot* argument should be either PROT\_NONE or the bitwise-inclusive OR of one or more of PROT\_READ, PROT\_WRITE, and PROT\_EXEC.

If an implementation cannot support the combination of access types specified by *prot*, the call to *mprotect*() shall fail.

An implementation may permit accesses other than those specified by *prot*; however, no implementation shall permit a write to succeed where PROT\_WRITE has not been set or shall permit any access where PROT\_NONE alone has been set. Implementations shall support at least the following values of *prot*: PROT\_NONE, PROT\_READ, PROT\_WRITE, and the bitwise-inclusive OR of PROT\_READ and PROT\_WRITE. If PROT\_WRITE is specified, the application shall ensure that it has opened the mapped objects in the specified address range with write permission, unless MAP\_PRIVATE was specified in the original mapping, regardless of whether the file descriptors used to map the objects have since been closed.

The implementation may require that *addr* be a multiple of the page size as returned by *sysconf*().

The behavior of this function is unspecified if the mapping was not established by a call to *mmap*().

When *mprotect*() fails for reasons other than **\[EINVAL\]**, the protections on some of the pages in the range \[*addr*,*addr*+*len*) may have been changed.

## RETURN VALUE

Upon successful completion, *mprotect*() shall return 0; otherwise, it shall return -1 and set *errno* to indicate the error.

## ERRORS

The *mprotect*() function shall fail if:

- **EACCES**

  The *prot* argument specifies a protection that violates the access permission the process has to the underlying memory object.

- **EAGAIN**

  The *prot* argument specifies PROT\_WRITE over a MAP\_PRIVATE mapping and there are insufficient memory resources to reserve for locking the private page.

- **ENOMEM**

  Addresses in the range \[*addr*,*addr*+*len*) are invalid for the address space of a process, or specify one or more pages which are not mapped.

- **ENOMEM**

  The *prot* argument specifies PROT\_WRITE on a MAP\_PRIVATE mapping, and it would require more space than the system is able to supply for locking the private pages, if required.

- **ENOTSUP**

  The implementation does not support the combination of accesses requested in the *prot* argument.

The *mprotect*() function may fail if:

- **EINVAL**

  The *addr* argument is not a multiple of the page size as returned by *sysconf*().

*The following sections are informative.*

## EXAMPLES

None.

## APPLICATION USAGE

Most implementations require that *addr* is a multiple of the page size as returned by *sysconf*().

## RATIONALE

None.

## FUTURE DIRECTIONS

None.

## SEE ALSO

*mmap()*, *sysconf()*

The Base Definitions volume of POSIX.1‐2017, ***\<sys\_mman.h\>***

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting\_bugs.html .