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Asked: 2026-05-10T21:49:57+00:00

Notice these two RedHat Linux system configuration settings: $ getconf GNU_LIBC_VERSION glibc 2.3.4 $

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Notice these two RedHat Linux system configuration settings:

$ getconf GNU_LIBC_VERSION glibc 2.3.4  $ getconf GNU_LIBPTHREAD_VERSION NPTL 2.3.4

I see they correspond to some of the TLS libraries:

/lib/tls/libc-2.3.4.so /lib/tls/libm-2.3.4.so /lib/tls/libpthread-2.3.4.so /lib/tls/librt-2.3.4.so

I’d like to link against these libraries instead of the /usr/lib equivalents. I have a few questions:

  1. I’ve seen this on RedHat and Debian. Does it exist on all GNU Linux distributions?
  2. Is there any case where GNU_LIBC_VERSION differs from GNU_LIBPTHREAD_VERSION?
  3. Are those variables safe to use for identifying the shared libraries in /lib/tls? I’d like to automate this in a Makefile, rather than hard-coding a magic glibc/pthread version number.
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1 Answer

  1. The NPTL project which first implemented pThreads on Linux was a separate project initially adding kernel support and providing its own library.

    When it was stable enough it was merged into glibc. I would assume that those two versions are identical on all reasonably up-to-date installations.

    On Ubuntu 8.10 the output is like this:

     $ getconf GNU_LIBC_VERSION glibc 2.8.90 $ getconf GNU_LIBPTHREAD_VERSION NPTL 2.8.90
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