docker run -it --platform linux/amd64 --volume ~/Downloads:/downloads ubuntu:latest
apt-get update
apt-get install binutils -y
cd /downloads
tar xf volta-linux.tar
objdump -T ./volta | grep GLIBC | sed 's/.*GLIBC_\([.0-9]*\).*/\1/g' | sort -Vu

Output:

2.2.5
2.3
2.3.4
2.4
2.9
2.12
2.14
2.15

Or with ldd:

ldd -v ./volta

	./volta:
		libdl.so.2 (GLIBC_2.2.5) => /lib/x86_64-linux-gnu/libdl.so.2
		ld-linux-x86-64.so.2 (GLIBC_2.3) => /lib64/ld-linux-x86-64.so.2
		librt.so.1 (GLIBC_2.2.5) => /lib/x86_64-linux-gnu/librt.so.1
		libm.so.6 (GLIBC_2.2.5) => /lib/x86_64-linux-gnu/libm.so.6
		libpthread.so.0 (GLIBC_2.12) => /lib/x86_64-linux-gnu/libpthread.so.0
		libpthread.so.0 (GLIBC_2.2.5) => /lib/x86_64-linux-gnu/libpthread.so.0
		libgcc_s.so.1 (GCC_3.0) => /lib/x86_64-linux-gnu/libgcc_s.so.1
		libgcc_s.so.1 (GCC_4.2.0) => /lib/x86_64-linux-gnu/libgcc_s.so.1
		libgcc_s.so.1 (GCC_3.3) => /lib/x86_64-linux-gnu/libgcc_s.so.1
		libc.so.6 (GLIBC_2.15) => /lib/x86_64-linux-gnu/libc.so.6
		libc.so.6 (GLIBC_2.14) => /lib/x86_64-linux-gnu/libc.so.6
		libc.so.6 (GLIBC_2.9) => /lib/x86_64-linux-gnu/libc.so.6
		libc.so.6 (GLIBC_2.4) => /lib/x86_64-linux-gnu/libc.so.6
		libc.so.6 (GLIBC_2.3.4) => /lib/x86_64-linux-gnu/libc.so.6
		libc.so.6 (GLIBC_2.3) => /lib/x86_64-linux-gnu/libc.so.6
		libc.so.6 (GLIBC_2.2.5) => /lib/x86_64-linux-gnu/libc.so.6

So I suppose 2.15 is the min version? But this doesn't match what Rust docs say

This said, if you get ubuntu 12.04 (shipping with glibc 2.15), running ./volta does work:

docker run -it --platform linux/amd64 --volume ~/Downloads:/downloads ubuntu:12.04

I suppose you might remain compatible with older glibc as long as you only use a subset of the standard library? But really not sure.

If that's the case, you'd have to check the min glibc version on CI, or just say that you support [whatever glibc your version of Rust supports] and make no promises about compatibility with earlier glibc versions.

Regarding semver — I don't feel like bumping the minimum supported version is a semver violation, because eg. a distro maintainer might build your binary with musl, or even with an alternative Rust compiler, and it will work fine on older machines.

This said, there's a long long argument about it at semver/semver#716, so evidently there are people who think any breaking change counts as breaking the API.

Unrelatedly, feel free to ping me on discord (@availablegreen) if you want me to check anything else re/ glibc

Thanks so much for that info and input, @neongreen! We have some discussion over on #1619 for why we're inclined to treat the change as breaking. The TL;DR is that in practice, the change in MSRV will break any Fedora/RHEL users who rely on the pre-Rust 1.64 glibc version (or other distros), and who are committed to staying on those unsupported distro versions for whatever reason. Given SemVer is primarily a matter of keeping whatever contract we establish, we can ultimately do what we want here, but it seems best to just do the clearest thing in this case: flag it as a small breaking change. Especially since this is a binary, not a library, major versions are mostly free.