---
name: "mprotect"
section: "2"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/mprotect"
---

# mprotect(2)

control the protection of pages

## NAME

**mprotect** – control the protection of pages

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<sys/mman.h\>**

*int*\

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

## DESCRIPTION

The **mprotect**() system call changes the specified pages to have protection *prot*.

The *prot* argument shall be PROT\_NONE (no permissions at all) or the bitwise *or* of one or more of the following values:

- PROT\_READ

  The pages can be read.

- PROT\_WRITE

  The pages can be written.

- PROT\_EXEC

  The pages can be executed.

In addition to these standard protection flags, the FreeBSD implementation of **mprotect**() provides the ability to set the maximum protection of a region (which prevents **mprotect** from adding to the permissions later). This is accomplished by bitwise *or*'ing one or more PROT\_ values wrapped in the PROT\_MAX() macro into the *prot* argument.

## RETURN VALUES

The **mprotect()** function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

## ERRORS

The **mprotect**() system call will fail if:

- \[EACCES\]

  The calling process was not allowed to change the protection to the value specified by the *prot* argument.

- \[EINVAL\]

  The virtual address range specified by the *addr* and *len* arguments is not valid.

- \[EINVAL\]

  The *prot* argument contains unhandled bits.

- \[ENOTSUP\]

  The *prot* argument contains permissions which are not a subset of the specified maximum permissions.

## SEE ALSO

[madvise(2)](/madvise/2.md), [mincore(2)](/mincore/2.md), [msync(2)](/msync/2.md), [munmap(2)](/munmap/2.md)

## HISTORY

The **mprotect**() system call was first documented in 4.2BSD and first appeared in 4.4BSD.

The PROT\_MAX functionality was introduced in FreeBSD 13.