macOS FS vs Linux FS - case sensitivity
Abstract
In this article, I will overview the case-sensitivity difference between macOS default filesystem (FS) and Linux filesystem with some practical examples and gotchas.
Intro
Unix and Linux might sound the same to some of us, but they are different beasts. macOS aka OS X or Max OS X is a Unix-based operating system, while Linux is Unix-like OS. There are many articles explaining the difference [1]. No need to repeat.
Experiment - maxOS FS case sensitivity
Let's do an experiment 🤓.
Assuming that you're running on macOS, create a file called entrypoint.sh with content:
#!/bin/bash
echo "hello"
Try running it as:
$ bash ./entrypoint.sh
hello
Now rename it to Entrypoint.sh (with capital E) and run again:
$ bash ./entrypoint.sh
hello
Works anyway! File names are case insensitive, meaning that you can run it even as:
$ bash ./eNtryPOInt.sh
hello
I don't know how about you, but when I found it for the first time I was really surprised. When working with a mac, on the surface, it looks and feels very Linuxy, the terminal, the shell, the commands, the paths... It's all been a lie 😭.
Let's see how case-sensitivity would work on Linux using Docker
Define a simple dockerfile:
FROM alpine:3.14
WORKDIR /poc
COPY ./Entrypoint.sh /poc/Entrypoint.sh
ENTRYPOINT ["/bin/sh", "/poc/entrypoint.sh" ]
Here we're copying the entrypoint.sh file and running it as the ENTRYPOINT command. Notice that we run the lowercased file but we copied in uppercased file!
Well, running it won't work since Linux filesystem is case-sensitive:
$ docker build -t macOS-FS . && docker run -t macOS-FS
/bin/sh: can't open '/poc/entrypoint.sh': No such file or directory
If we change the entrypoint to /poc/Entrypoint.sh it should work. Try it yourself!
FS case-sensitivity and Git
Another thing to note is that since FS is case-insensitive, these changes will not be tracked in Git 😶. I know! Quite shocking to stop thinking of Git as the source of the absolute truth of text-based file changes! The same experiment can be done by renaming one of the tracked files and seeing the Git-detected changes 🤯. It got me personally multiple times over the past years when programs worked locally but failed to launch in Linux-based containers or in my lovely CI/CD pipelines.
Using macOS case-sensitive file system
It's possible to have a case-sensitive filesystem on macOS. For that, we need to set the disc to use APFS (Case-sensitive) format: "APFS (Case-sensitive): Uses the APFS format, is case-sensitive to file and folder names. For example, folders named “Homework” and “HOMEWORK” are two different folders." [2].
However, it might be risky. Most macOS applications don’t recognize a case-sensitive file system. And probably won’t work as expected. So wouldn't recommend it. On the other hand, it might make sense to set a separate partition on your drive to be case-sensitive, especially if you work with Linux-based systems quite often. But not the whole drive.
Conclusion
macOS and Linux might look and feel the same, but in reality, they are quite different. Filesystem case sensitivity is only one example of such diffrence. I hope that this short overview of case-sensitivity differences was useful. And you won't be caught off-guard next time your application won't run when Git didn't pick up on file rename changes on macOS.