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I have a C program on Ubuntu 16.04, in which I would like to use arc4random_uniform.

typedef unsigned char u_char;
#include <bsd/stdlib.h>
int main () { return (int) arc4random_uniform(100); }

Hopefully, this will return to the OS with a random exit code between 0 and 100. Compiling it:

$ gcc -o rand_test ./rand_test.c -lbsd 
/tmp/ccGL6qmU.o: In function `main':
:(.text+0xa): undefined reference to `arc4random_uniform'
collect2: error: ld returned 1 exit status

Package libbsd-dev provides /usr/include/bsd/stdlib.h. This file looks like:

/*
 * Copyright © 2005 Aurelien Jarno
 * Copyright © 2006 Robert Millan
 * Copyright © 2008-2011 Guillem Jover <guillem@hadrons.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
 * THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifdef LIBBSD_OVERLAY
#include_next <stdlib.h>
#else
#include <stdlib.h>
#endif

/* For compatibility with NetBSD, which defines humanize_number here. */
#ifdef LIBBSD_OVERLAY
#include <libutil.h>
#else
#include <bsd/libutil.h>
#endif

#ifndef LIBBSD_STDLIB_H
#define LIBBSD_STDLIB_H

#include <sys/cdefs.h>
#include <sys/stat.h>
#include <stdint.h>

__BEGIN_DECLS
uint32_t arc4random(void);
void arc4random_stir(void);
void arc4random_addrandom(u_char *dat, int datlen);
void arc4random_buf(void *_buf, size_t n);
uint32_t arc4random_uniform(uint32_t upper_bound);

int dehumanize_number(const char *str, int64_t *size);

const char *getprogname(void);
void setprogname(const char *);

int heapsort (void *, size_t, size_t, int (*)(const void *, const void *));
int mergesort(void *base, size_t nmemb, size_t size,
              int (*cmp)(const void *, const void *));
int radixsort(const unsigned char **base, int nmemb,
              const unsigned char *table, unsigned endbyte);
int sradixsort(const unsigned char **base, int nmemb,
               const unsigned char *table, unsigned endbyte);

void *reallocf(void *ptr, size_t size);
void *reallocarray(void *ptr, size_t nmemb, size_t size);

long long strtonum(const char *nptr, long long minval, long long maxval,
                   const char **errstr);

char *getbsize(int *headerlenp, long *blocksizep);
__END_DECLS

#endif

It contains declarations, but no actual functions. pkg-config --libs libbsd prints -lbsd (which I already compiled with).

The following packages are installed:

libbsd-dev/xenial,now 0.8.2-1 amd64 [installed]
  utility functions from BSD systems - development files

libbsd0/xenial,now 0.8.2-1 amd64 [installed]
  utility functions from BSD systems - shared library

man 3 arc4random_uniform says:

LIBRARY
    Utility functions from BSD systems (libbsd, -lbsd)

SYNOPSIS
    #include <bsd/stdlib.h>

That certainly sounds like #include <bsd/stdlib.h> and gcc ... -lbsd should get it to work, but it doesn't.

Can I use arc4random_uniform and friends on Linux? Which header should I include, or package should I install, to find these functions' declarations?

Here's the result of the commands suggested in the comments:

cat @ mint-kitty : ~/projects/c/junk $ cat > rand_test.c
typedef unsigned char u_char;
#include <bsd/stdlib.h>
int main () { return (int) arc4random_uniform(100); }

cat @ mint-kitty : ~/projects/c/junk $ gcc -o rand_test ./rand_test.c -Wl,--verbose -lbsd | grep bsd
attempt to open /usr/lib/gcc/x86_64-linux-gnu/5/libbsd.so failed
attempt to open /usr/lib/gcc/x86_64-linux-gnu/5/libbsd.a failed
attempt to open /usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/libbsd.so succeeded
-lbsd (/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/libbsd.so)

cat @ mint-kitty : ~/projects/c/junk $ ls -l /lib/x86_64-linux-gnu/libbsd*
lrwxrwxrwx 1 root root    15 Jan 28 00:11 /lib/x86_64-linux-gnu/libbsd.so.0 -> libbsd.so.0.8.2
-rw-r--r-- 1 root root 81040 Jan 28 00:11 /lib/x86_64-linux-gnu/libbsd.so.0.8.2
  • It works for me, with libbsd-dev 0.8.3-1... What does pkg-config --libs libbsd say? – Stephen Kitt May 10 '16 at 15:49
  • @StephenKitt It says -lbsd, but linking with -lsbd doesn't work. – cat May 10 '16 at 15:53
  • You could check to see how the linker attempts to resolve it e.g. gcc-5 -o rand_test ./rand_test.c -Wl,--verbose -lbsd | grep bsd. BTW what does ls -l /lib/x86_64-linux-gnu/libbsd* return? (perhaps there is a broken link?) – steeldriver May 10 '16 at 17:42
  • @steeldriver It seems there are no broken links? pastebin.com/qXBUwg0N – cat May 10 '16 at 17:50
  • ... and presumably you can see the objects with nm -D /lib/x86_64-linux-gnu/libbsd.so.0 | grep arc or equivalent? – steeldriver May 10 '16 at 20:34

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