NAME

       getentropy - fill a buffer with random bytes

SYNOPSIS

       #include <unistd.h>

       int getentropy(void *buffer, 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 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.

       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)

COLOPHON

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