Operating system kernel (kernel): realizes the core functions of the operating system: memory management, process management, file system management and device management.
System call (system call): function similar to C language, about two hundred. System call is the smallest functional unit of the operating system, but the function is too simple and cumbersome to use.
Library function (library): It is a collection of functions with certain functions established by the system. The role is to combine system calls into some commonly used functions.
Shell (command interpreter - interpreter): the command line, used for human-computer interaction.
In Linux, everything is a file
Linux uses a standard tree directory structure, the top directory is the root directory, and other subdirectories are generated from the root directory.
A file path, formally consisting of multiple filenames separated by slashes /. All but the last filename must represent a directory. Paths starting with a slash are called absolute paths and will be looked up from the root directory. Paths that do not start with a slash are called relative paths and will be searched from the current directory.