Show major/minor numbers of a mountpoint's filesystem

Test if a directory is a filesystem mountpoint.
More information: <https://manned.org/mountpoint>.
Trick copyright: tl;dr; <https://github.com/tldr-pages/tldr>

mountpoint --fs-devno {{path/to/directory}}

click the source code to copy install mountpoint on any operating system with command-not-found.com