On success, a call to mmap() returns the location of the mapping. On failure, the call returns MAP_FAILED , and sets errno appropriately. A call to mmap() never returns 0.

Possible errno values include:

EACCES S
   The given file descriptor is not a regular file, or the
   mode with which it was opened conflicts with prot
   or flags .

EAGAIN
   The file has been locked via a file lock.

EBADF
   The given file descriptor is not valid.

EINVAL
   One or more of the parameters addr , len , or off
   are invalid.

ENFILE
   The system-wide limit on open files has been
   reached.

ENODEV
   The filesystem on which the file to map resides does
   not support memory mapping.

ENOMEM
   The process does not have enough memory.

EOVERFLOW
   The result of addr+len exceeds the size of the
   address space.

EPERM 
   PROT_EXEC was given, but the filesystem is mounted 
 noexec .