{"id":7073,"date":"2022-12-20T19:35:11","date_gmt":"2022-12-20T22:35:11","guid":{"rendered":"http:\/\/lode.uno\/linux-man\/index.php\/2022\/12\/20\/getentropy-man3\/"},"modified":"2022-12-20T19:35:11","modified_gmt":"2022-12-20T22:35:11","slug":"getentropy-man3","status":"publish","type":"post","link":"https:\/\/lode.uno\/linux-man\/2022\/12\/20\/getentropy-man3\/","title":{"rendered":"GETENTROPY (man3)"},"content":{"rendered":"

GETENTROPY<\/h1>\n

NAME<\/a>
SYNOPSIS<\/a>
DESCRIPTION<\/a>
RETURN VALUE<\/a>
ERRORS<\/a>
VERSIONS<\/a>
CONFORMING TO<\/a>
NOTES<\/a>
SEE ALSO<\/a>
COLOPHON<\/a> <\/p>\n

\n

NAME <\/a> <\/h2>\n

getentropy \u2212 fill a buffer with random bytes<\/p>\n

SYNOPSIS <\/a> <\/h2>\n

#include <\/b><\/p>\n

int getentropy(void *<\/b>buffer<\/i>, size_t<\/b> length<\/i>);<\/b><\/p>\n

Feature Test Macro Requirements for glibc (see feature_test_macros<\/b>(7)):<\/p>\n

getentropy<\/b>():<\/p>\n

_DEFAULT_SOURCE<\/p>\n

DESCRIPTION <\/a> <\/h2>\n

The getentropy<\/b>() function writes length<\/i> bytes of high-quality random data to the buffer starting at the location pointed to by buffer<\/i>. The maximum permitted value for the length<\/i> argument is 256.<\/p>\n

A successful call to getentropy<\/b>() always provides the requested number of bytes of entropy.<\/p>\n

RETURN VALUE <\/a> <\/h2>\n

On success, this function returns zero. On error, \u22121 is returned, and errno<\/i> is set appropriately.<\/p>\n

ERRORS <\/a> <\/h2>\n\n\n\n\n\n
<\/td>\n\n

EFAULT<\/b><\/p>\n<\/td>\n

<\/td>\n\n

Part or all of the buffer specified by buffer<\/i> and length<\/i> is not in valid addressable memory.<\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

EIO<\/b><\/p>\n<\/td>\n

<\/td>\n\n

length<\/i> is greater than 256.<\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

EIO<\/b><\/p>\n<\/td>\n

<\/td>\n\n

An unspecified error occurred while trying to overwrite buffer<\/i> with random data.<\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

ENOSYS<\/b><\/p>\n<\/td>\n

<\/td>\n\n

This kernel version does not implement the getrandom<\/b>(2) system call required to implement this function.<\/p>\n<\/td>\n<\/tr>\n<\/table>\n

VERSIONS <\/a> <\/h2>\n

The getentropy<\/b>() function first appeared in glibc 2.25.<\/p>\n

CONFORMING TO <\/a> <\/h2>\n

This function is nonstandard. It is also present on OpenBSD.<\/p>\n

NOTES <\/a> <\/h2>\n

The getentropy<\/b>() function is implemented using getrandom<\/b>(2).<\/p>\n

Whereas the glibc wrapper makes getrandom<\/b>(2) a cancellation point, getentropy<\/b>() is not a cancellation point.<\/p>\n

getentropy<\/b>() is also declared in <\/b>. (No feature test macro need be defined to obtain the declaration from that header file.)<\/p>\n

A call to getentropy<\/b>() 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<\/b>() will keep blocking even if a signal is handled, and will return only once the entropy pool has been initialized.<\/p>\n

SEE ALSO <\/a> <\/h2>\n

getrandom<\/b>(2), urandom<\/b>(4), random<\/b>(7)<\/p>\n

COLOPHON <\/a> <\/h2>\n

This page is part of release 5.10 of the Linux man-pages<\/i> project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https:\/\/www.kernel.org\/doc\/man\u2212pages\/.<\/p>\n

\n","protected":false},"excerpt":{"rendered":"

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