title: Various glibc and Linux kernel versions compatibility
body: <p>When building a compiler, one must specify Linux headers version and minumum supported kernel version, in addition to glibc version. And then there is actual kernel version and glibc version (with its own kernel headers version and minumum supported kernel version) on the target machine. I'm rather confused trying to understand how these versions go together.</p>
  
  <p>Example 1: Assume I have system with glibc <em>2.13</em> built against kernel headers <em>3.14</em>. Does that make any sense? How is it possible for glibc <em>2.13</em> (released in 2011) to use new kernel features from <em>3.14</em> (released in 2014)?</p>
  
  <p>Example 2: Assume I have a compiler with glibc version <strong>newer</strong> than <em>2.13</em>. Will compiled programs work on system with glibc <em>2.13</em>? And if compiler's glibc version is <strong>older</strong> than <em>2.13</em>?</p>
  
  <p>Example 3: From <a href="https://sourceware.org/glibc/wiki/FAQ#What_version_of_the_Linux_kernel_headers_should_be_used.3F" rel="noreferrer">https://sourceware.org/glibc/wiki/FAQ#What_version_of_the_Linux_kernel_headers_should_be_used.3F</a> I understand that it's OK to use older kernel if it satisfies "minumum kernel version" used when compiling glibc. But I don't understand the passage <code>The other way round (compiling the GNU C library with old kernel headers and running on a recent kernel) does not necessarily work as expected. For example you can't use new kernel features if you used old kernel headers to compile the GNU C library.</code>. Is it the only thing that can happen to me? Won't it break something in glibc if the kernel is newer than at compile-time?</p>
  
  <p>Example 4: Do more subtle differences in glibc settings (for example, linking an executable against glibc version <em>2.X</em> compiled against kernel headers <em>3.Y</em> with minimum supported kernel version <em>2.6.A</em> and executing in on system with the same glibc <em>2.X</em>, but compiled against kernel headers <em>3.Z</em> with minumum supported kernel version <em>2.6.B</em>) influence anything? I suspect they're not, but would like to be sure.</p>
  
  <p>So many questions :) Thanks!</p>