The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


mprotect - set protection of memory mapping


#include <sys/mman.h>

int mprotect(void *addr, size_t len, int prot);


The function mprotect() changes 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() fails.

An implementation may permit accesses other than those specified by prot; however, no implementation permits a write to succeed where PROT_WRITE has not been set or permits any access where PROT_NONE alone has been set. Implementations will support at least the following values of prot: PROT_NONE, PROT_READ, PROT_WRITE, and the inclusive OR of PROT_READ and PROT_WRITE. If PROT_WRITE is specified, the application must have 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  will require that addr be a multiple of the page size as returned by sysconf().

The behaviour 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.


Upon successful completion, mprotect() returns 0. Otherwise, it returns -1 and sets errno to indicate the error.


The mprotect() function will fail if:
The prot argument specifies a protection that violates the access permission the process has to the underlying memory object.
The prot argument specifies PROT_WRITE over a MAP_PRIVATE mapping and there are insufficient memory resources to reserve for locking the private page.
The addr argument is not a multiple of the page size as returned by sysconf().
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.
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.
The implementation does not support the combination of accesses requested in the prot argument.




The EINVAL error above is marked EX because it is defined as an optional error in the POSIX Realtime Extension.




mmap(), sysconf(), <sys/mman.h>.

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Copyright © 1997 The Open Group
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