NAME

       getentropy - fill a buffer with random bytes

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <unistd.h>

       int getentropy(void buffer[.length], size_t length);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getentropy():
           _DEFAULT_SOURCE

DESCRIPTION

       The  getentropy()  function writes length bytes of high-quality random data to the buffer starting at the
       location pointed to by buffer.  The maximum permitted value for the length argument is 256.

       A successful call to getentropy() always provides the requested number of bytes of entropy.

RETURN VALUE

       On success, this function returns zero.  On error, -1 is returned, and  errno  is  set  to  indicate  the
       error.

ERRORS

       EFAULT Part or all of the buffer specified by buffer and length is not in valid addressable memory.

       EIO    length is greater than 256.

       EIO    An unspecified error occurred while trying to overwrite buffer with random data.

       ENOSYS This  kernel  version  does  not implement the getrandom(2) system call required to implement this
              function.

STANDARDS

       None.

HISTORY

       glibc 2.25.  OpenBSD.

NOTES

       The getentropy() function is implemented using getrandom(2).

       Whereas the glibc wrapper makes getrandom(2) a cancelation  point,  getentropy()  is  not  a  cancelation
       point.

       getentropy()  is  also  declared in <sys/random.h>.  (No feature test macro need be defined to obtain the
       declaration from that header file.)

       A call to getentropy() may block if the system has just booted and  the  kernel  has  not  yet  collected
       enough  randomness to initialize the entropy pool.  In this case, getentropy() will keep blocking even if
       a signal is handled, and will return only once the entropy pool has been initialized.

SEE ALSO

       getrandom(2), urandom(4), random(7)