Once upon a time, it was common to have time-shared multiuser Unix systems – a single server and everyone in the department could login and use it simultaneousl

Once upon a time, it was common to have time-shared multiuser Unix systems – a single server and everyone in the department could login and use it simultaneously. Filesystem permissions – first the classic mode bits, then ACLs – were originally designed for that use case. While such systems still exist, they are a much smaller percentage of all installed systems than they used to be. Most contemporary Unix(-like) systems fall into one of two categories: (a) single-user machines (such as a laptop) (b) application servers, database servers, etc, which serve many users, but those users are defined at the application layer, the OS and filesystem don't know anything about them Maybe part of the reason why filesystem ACL adoption is weaker than people expected, is that (a) and (b) don't have the same need for filesystem ACLs as the classic multi-user timesharing environments do. > But the most common Linux distributions are Android which make extensive use of SELinux features SELinux context and filesystem ACLs are two separate things. I see many machines with heaps of the former and little of the later (such as most Red Hat boxes). Even with single-user machines, there is still some value in inter-process security – application sandboxing, corporate-managed devices, etc – but there are many technologies available now to meet those requirements, and filesystem ACLs are often not the most useful among them.