文件系统

In order for a Linux system to run, it typically needs two file systems:

1. boot file system (bootfs)
2. root file system (rootfs)

The boot file system contains the bootloader and the kernel. The user never makes any changes to the boot file system. In fact, soon after the boot process is complete, the entire kernel is in memory, and the boot file system is unmounted to free up the RAM associated with the initrd disk image.

The root file system includes the typical directory structure we associate with Unix-like operating systems: /dev, /proc, /bin, /etc, /lib, /usr, and /tmp plus all the configuration files, binaries and libraries required to run user applications (like bash, ls, and so forth).

While there can be important kernel differences between different Linux distributions, the contents and organization of the root file system are usually what make your software packages dependent on one distribution versus another. Docker can help solve this problem by running multiple distributions at the same time.