getentropy(3) Library Functions Manual getentropy(3)NAME top
getentropy - fill a buffer with random bytesLIBRARY top
Standard C library (libc, -lc)SYNOPSIS top
#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 top
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 top
On success, this function returns zero. On error, -1 is returned,
and errno is set to indicate the error.
ERRORS top
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 top
None.HISTORY top
glibc 2.25. OpenBSD.NOTES top
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 top
getrandom(2), urandom(4), random(7)COLOPHON top
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Pages that refer to this page: getrandom(2), random(7)
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