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3.1.2. Unifying File Systems
File systems are a prominent aspect of the kernel. Unix-like systems merge all the file stores into a single hierarchy, which allows users and applications to access data by knowing its location within that hierarchy.
The starting point of this hierarchical tree is called the root, represented by the “/” character. This directory can contain named subdirectories. For instance, the home subdirectory of / is called
/home/. This subdirectory can, in turn, contain other subdirectories, and so on. Each directory can also contain files, where the data will be stored. Thus, /home/buxy/Desktop/hello.txt refers to a file named hello.txt stored in the Desktop subdirectory of the buxy subdirectory of the home directory, present in the root. The kernel translates between this naming system and the storage location on a disk.
Unlike other systems, Linux possesses only one such hierarchy, and it can integrate data from several disks. One of these disks becomes the root, and the others are mounted on directories in the hierarchy (the Linux command is called mount). These other disks are then available under the mount points. This allows storing users’ home directories (traditionally stored within /home/) on a separate hard disk, which will contain the buxy directory (along with home directories of other users). Once you mount the disk on /home/, these directories become accessible at their usual locations, and paths such as /home/buxy/Desktop/hello.txt keep working.
There are many file system formats, corresponding to many ways of physically storing data on disks. The most widely known are ext2, ext3, and ext4, but others exist. For instance, VFAT is the filesystem that was historically used by DOS and Windows operating systems. Linux’s support for VFAT allows hard disks to be accessible under Kali as well as under Windows. In any case, you must prepare a file system on a disk before you can mount it and this operation is known as formatting.
Commands such as mkfs.ext3 (where mkfs stands for MaKe FileSystem) handle formatting. These commands require, as a parameter, a device file representing the partition to be formatted (for instance, /dev/sda1, the first partition on the first drive). This operation is destructive and should be run only once, unless you want to wipe a filesystem and start fresh.
There are also network filesystems such as NFS, which do not store data on a local disk. Instead, data are transmitted through the network to a server that stores and retrieves them on demand. Thanks to the file system abstraction, you don’t have to worry about how this disk is connected, since the files remain accessible in their usual hierarchical way.