A recent post reminded me of a problem I once had; determine the glibc version and its support for various things.
There's actually a little known but useful confstr call defined for just this sort of thing. Here's a minimal example:
#include <stdio.h>
#include <unistd.h>
#include <alloca.h>
#include <string.h>
int main (void)
{
size_t n = confstr (_CS_GNU_LIBC_VERSION, NULL, 0);
if (n > 0)
{
char *buf = alloca (n);
confstr (_CS_GNU_LIBC_VERSION, buf, n);
printf("%s\n", buf);
}
return 0;
}
man confstr has all the details. If you don't need it in your program, you can also just run /lib/libc/so.6 and it will print out it's version info, e.g.
$ /lib/libc.so.6
GNU C Library stable release version 2.7, by Roland McGrath et al.
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 4.3.1 20080523 (prerelease).
Compiled on a Linux >>2.6.24.4<< system on 2008-06-02.
Available extensions:
crypt add-on version 2.1 by Michael Glad and others
GNU Libidn by Simon Josefsson
Native POSIX Threads Library by Ulrich Drepper et al
BIND-8.2.3-T5B
For bug reporting instructions, please see:
<http://www.gnu.org/software/libc/bugs.html>.
There's also another glibc trick that often comes in useful; the LD_DEBUG environment variable. Start with help and you can get more details from there.
$ LD_DEBUG=help ls Valid options for the LD_DEBUG environment variable are: libs display library search paths reloc display relocation processing files display progress for input file symbols display symbol table processing bindings display information about symbol binding versions display version dependencies all all previous options combined statistics display relocation statistics unused determined unused DSOs help display this help message and exit To direct the debugging output into a file instead of standard output a filename can be specified using the LD_DEBUG_OUTPUT environment variable.