getentropy(3)                                         Library Functions Manual                                        getentropy(3)

       getentropy - fill a buffer with random bytes

       Standard C library (libc, -lc)

       #include <unistd.h>

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

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


       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.

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

       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.

       The getentropy() function first appeared in glibc 2.25.

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

       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.

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

Linux man-pages 6.03                                         2022-11-10                                               getentropy(3)