See also https://reproducible-builds.org/docs/stable-inputs/ According to POSIX specs, readdir can return entries in a directory in random order, though the specifics depend on the underlying filesystem. On Linux with ext4 it is pretty random. Observed in the wild: Python: https://github.com/dahlia/libsass-python/pull/212/files https://github.com/mypaint/libmypaint/pull/108/files https://github.com/skyjake/Doomsday-Engine/pull/18/files https://github.com/kovidgoyal/html5-parser/pull/5/files https://github.com/dugsong/libdnet/pull/42/files https://github.com/carlos-jenkins/nested/pull/1/files C: https://sourceforge.net/p/blobwars/patches/8/ Make (reproducible with glob-sort patch at https://savannah.gnu.org/bugs/?52076): https://github.com/dunst-project/dunst/pull/372/files shell/find: https://github.com/crawl/crawl/pull/609/files http://dpdk.org/dev/patchwork/patch/29949/ LISP: https://github.com/SawfishWM/librep/pull/12/files Rust: rust-lang/git2-rs#619