The root filesystem and mount points

As a Linux system boots, the first filesystem that becomes available is the top level, or root filesystem, denoted with a single forward slash. The root filesystem /, also known as the root directory, shouldn’t be confused with the root superuser account or the superuser’s home directory, /root. The distinct directories / and /root are unrelated and are not required to share the same filesystem. In a simple installation, the root filesystem could contain nearly everything on the system. However, such an arrangement could lead to system failure if the root filesystem fills to capacity. Instead, multiple partitions are typically defined, each containing one of the directories under /. As the Linux kernel boots, the partitions are mounted to the root filesystem, and together create a single unified filesystem (see Objective 3: Control Filesystem Mounting and Unmounting for a discussion about mounting). Everything on the system that is not stored in a mounted partition is stored locally in the / (root) partition. The mounted filesystems are placed on separate partitions and possibly multiple disk drives.

The choice of which directories are placed into separate partitions is both a personal and technical decision. Here are some guidelines for individual partitions:

/ (the root directory)

Since the only filesystem mounted at the start of the boot process is /, certain directories must be part of it to be available for the boot process. These include: ...

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