Manpages - getentropy.3

getentropy - fill a buffer with random bytes

  #include <unistd.h>

  int getentropy(void *buffer, size_t length);

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

*getentropy*():

      _DEFAULT_SOURCE

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 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.

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

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