GETENTROPY(3)		   Linux Programmer's Manual		 GETENTROPY(3)



NAME
       getentropy - fill a buffer with random bytes

SYNOPSIS
       #include <sys/random.h>

       getentropy(void *buffer, size_t length);

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 returns the requested number
       of bytes of entropy.

RETURN VALUE
       On success, this function returns zero, On error, -1 is	returned,  and
       errno is set appropriately.

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.

VERSIONS
       The getentropy() function first appeared in glibc 2.25.

CONFORMING TO
       This function is nonstandard.  It is also present on OpenBSD.

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

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

       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)

COLOPHON
       This  page  is  part of release 4.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest	  version     of     this    page,    can    be	   found    at
       https://www.kernel.org/doc/man-pages/.



Linux				  2017-01-22			 GETENTROPY(3)