Ubuntu – Why are these directories called file systems

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/proc, /usr, /var, /home are called file systems.

What does that mean? i thought there was only one file system (e.g. ext4)..

Best Answer

The term "file system" has several meanings. When people talk about the file system names like ext4, UFS, NTFS etc. they have in mind the organization of data storage at low level (in terms of blocks on media). Such "file systems" usually requires driver to access data stored on media formatted with that file system. In the case of /proc, /usr, root file system or something file system simply refers to a directory structure.

Technically in Linux any directory can be a mount point for file system. This allows you to select the best type of file system (ext4, ufs, xfs etc.) for individual directories, depending on the nature of the stored information and security requirements.

I believe in your case those directories are called "file systems" because they are are often used as a mount point for individual file systems. /proc is always a mount point for the procfs pseudo-file system that presents information about processes and other system information in a hierarchical file-like structure.

There are a few directories which can be considered file systems: /dev, /sys and /tmp.

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