Code change:
COPY host-x86_64/dist-x86_64-linux/build-binutils.sh /tmp/ RUN ./build-binutils.sh <del> # libssh2 (a dependency of Cargo) requires cmake 2.8.11 or higher but CentOS # only has 2.6.4, so build our own COPY host-x86_64/dist-x86_64-linux/build-cmake.sh /tmp/ RUN ./build-cmake.sh # Build a version of gcc capable of building LLVM 6 </del> <ins> # Need at least GCC 5.1 to compile LLVM nowadays </ins> COPY host-x86_64/dist-x86_64-linux/build-gcc.sh /tmp/ <del> RUN ./build-gcc.sh </del> <ins> RUN ./build-gcc.sh && apt-get remove -y gcc g++ </ins> <del> # CentOS 5.5 has Python 2.4 by default, but LLVM needs 2.7+ </del> <ins> # Debian 6 has Python 2.6 by default, but LLVM needs 2.7+ </ins> COPY host-x86_64/dist-x86_64-linux/build-python.sh /tmp/ RUN ./build-python.sh <del> # Now build LLVM+Clang 7, afterwards configuring further compilations to use the </del> <ins> # LLVM needs cmake 3.4.3 or higher, and is planning to raise to 3.13.4. COPY host-x86_64/dist-x86_64-linux/build-cmake.sh /tmp/ RUN ./build-cmake.sh # Now build LLVM+Clang, afterwards configuring further compilations to use the </ins> # clang/clang++ compilers. <del> COPY host-x86_64/dist-x86_64-linux/build-clang.sh host-x86_64/dist-x86_64-linux/llvm-project-centos.patch /tmp/ </del> <ins> COPY host-x86_64/dist-x86_64-linux/build-clang.sh /tmp/ </ins> RUN ./build-clang.sh ENV CC=clang CXX=clang++ <del> # Apparently CentOS 5.5 desn't have `git` in yum, but we're gonna need it for # cloning, so download and build it here. COPY host-x86_64/dist-x86_64-linux/build-git.sh /tmp/ RUN ./build-git.sh # for sanitizers, we need kernel headers files newer than the ones CentOS ships # with so we install newer ones here COPY host-x86_64/dist-x86_64-linux/build-headers.sh /tmp/ RUN ./build-headers.sh # OpenSSL requires a more recent version of perl # with so we install newer ones here COPY host-x86_64/dist-x86_64-linux/build-perl.sh /tmp/ RUN ./build-perl.sh </del> COPY scripts/sccache.sh /scripts/ RUN sh /scripts/sccache.sh

Related discussion:
text: If there are any known issues with such Linux compatibility code, I am definitely willing to take assignment for fixing them.
(Not a Rust maintainer, but I'm a Rust user and maintain a lot of other OSS software so I have well-developed feelings around supporting Very Old Software :-)) Do you have any sense of on what timeline Rust would be able to drop support for 2.6.18 kernels without causing you pain? In general I don't think people mind supporting configurations that have users and are painful to work around, but needing to support them for forever is a bitter pill to swallow! Particularly as they get harder and harder to test over time (already I have no idea how to test on really old kernels besides building it myself). So if there was an estimate "we'd like to be able to support this until Q2 2020", even if it's not set in stone, I think that would be very helpful!
The other benefit would be that Rust wouldn't have to use CentOS 5 for CI, which means we don't have to patch LLVM (and Emscripten LLVM) to compile on those systems. Of course that's also fairly limited in scope.
As soon as we stop shipping Firefox and Thunderbird updates on RHEL 6, I won't need Rust there anymore. AFAIK this does correspond to the end of Maintenance Support, November 30, 2020. Then I'll be on to RHEL 7 builders as my minimum, probably still with some RHEL 6 2.6.32 kernels involved. It should be fine for me if we update CI to CentOS 6. This is mostly concerned with how the release binaries are linked to GLIBC symbol versions, which is all in userspace. It's a broader community question whether any other Rust users still care about running on RHEL or CentOS 5. (Small caveat - glibc support for a symbol can still return , .)
I noticed that Red Hat also has Extended Life Cycle Support (ELS) for RHEL 6 until June 30, 2024. Will you need RHEL 5 to work during this time? I don't know how ELS works with Firefox updates. Also, is there any reason RHEL 4 support wasn't an issue prior to March 31, 2017 (while RHEL 5 was still normally supported)?