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GETENTROPY(3) Library Functions Manual GETENTROPY(3) NAME getentropy -- get entropy LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <unistd.h> int getentropy(void *buf, size_t buflen); DESCRIPTION getentropy() fills a buffer with high-quality random data. The maximum buflen permitted is 256 bytes. If it does not produce an error, getentropy() always provides the re- quested number of bytes of random data. Similar to reading from /dev/urandom just after boot, getentropy() may block until the system has collected enough entropy to seed the CSPRNG. IMPLEMENTATION NOTES The getentropy() function is implemented using getrandom(2). RETURN VALUES Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ERRORS getentropy() will succeed unless: [EFAULT] The buf parameter points to an invalid address. [EINVAL] Too many bytes requested. SEE ALSO getrandom(2), arc4random(3), random(4) STANDARDS getentropy() conforms to . HISTORY The getentropy() function appeared in OpenBSD 5.6. The FreeBSD libc compatibility shim first appeared in FreeBSD 12.0. FreeBSD 14.3 January 17, 2025 GETENTROPY(3)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | IMPLEMENTATION NOTES | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY
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