NAME
getrandom —
get random data
LIBRARY
library “libc”
SYNOPSIS
#include
<sys/random.h>
ssize_t
getrandom(void
*buf, size_t
buflen, unsigned int
flags);
DESCRIPTION
getrandom()
fills buf with up to buflen bytes
of random data.
The flags argument may include zero or more of the following:
- ‘
GRND_NONBLOCK’ - Return
EAGAINinstead of blocking, if the random(4) device has not yet been seeded. By default,getrandom() will block until the device is seeded. - ‘
GRND_RANDOM’ - This flag does nothing on FreeBSD. /dev/random and /dev/urandom are identical.
- ‘
GRND_INSECURE’ - This flag is treated as an alternative name for
GRND_NONBLOCK. It is provided solely for API compatibility with Linux.
If the random(4) device has been seeded, reads of up to 256 bytes will always return as many bytes as requested and will not be interrupted by signals.
RETURN VALUES
Upon successful completion, the number of bytes which were actually read is returned. For requests larger than 256 bytes, this can be fewer bytes than were requested. Otherwise, -1 is returned and the global variable errno is set to indicate the error.
ERRORS
The getrandom() operation returns the
following errors:
- [
EAGAIN] - The ‘
GRND_NONBLOCK’ (or ‘GRND_INSECURE’) flag was set and the random(4) device was not yet seeded. - [
EFAULT] - The buf parameter points to an invalid address.
- [
EINTR] - The sleep was interrupted by a signal.
- [
EINVAL] - An invalid flags was specified.
- [
EINVAL] - The requested buflen was larger than
IOSIZE_MAX.
SEE ALSO
STANDARDS
getrandom() is non-standard. It is present
in Linux.
HISTORY
The getrandom() system call first appeared
in FreeBSD 12.0.
CAVEATS
Unlike Linux, the GRND_INSECURE flag on
FreeBSD does not produce any output before the
random(4) device is seeded.