E01

 The Linux Filesystem

• A Linux operating system's built-in layer called the Linux file system is typically used to manage storage device data.
• The structure of the Linux file system is tree-like. The directory tree is another name for the structure that resembles a tree.It controls a file's name, size, creation date, and a tonne of other details.
• Representing and organising the system's storage resources is the fundamental function of a filesystem.
• Other files and folders can be found in its root directory.

Pathnames

• A pathname is a text string consisting of one or more names, such as assignment 02 /check, /var/log/auth.log,./etc/passwd, etc., separated by forward slashes (/).
• A pathname is a series of names that tells the hierarchical file system tree where to find a certain item.
• Pathnames that begin with a slash specify locations that are relative to the root of the pathname space (/). 

          For example:

                     - /home

                     - /etc/password

                     - usr /wc

                     - /vaar/ntpstats loopstats 

• The filesystem is shown as a single, cohesive structure that descends via an infinite number of subdirectories from the directory.
• Another name for the root directory is /.
• Under a single tree hierarchical file system structure, Unix/Linux files are arranged into directories that may contain additional subdirectories and files, as well as files that contain data (such as documents and programmes).

File Type in Linux

• Everything in a Linux system is a file, and everything that isn't a file is a process.
• Seven different file types are defined by most file system implementations.
• Developers must still make the file tree appear like one of these seven categories even when they add something amazing and unique, like the process information beneath /.

1. Regular files
2. Directories
3. Character device files
4. Block device files
5. Local domain sockets
6. Named pipes (FIFO)
7. Link files

Regular or Ordinary files

• Text, music, video, photos, scripts, and programmes are just a few of the content kinds that may be stored in regular or ordinary files.
• The vast majority of files on Linux and UNIX are standard files.
• Regular files in Linux can be generated either way around an extension.
• Standard files begin with -

Directories

• Named references to other files can be found within a directory. 
• It is a binary file that is used to find and track other directories and files.
• Directories can be created using mkdir and, if they are empty, deleted using rmdir. 
• Directories are used by file systems to arrange files in a hierarchy.
• A directory called /, or the root directory, is where the Linux file system begins. 
• This directory is where all files and directory files are produced. Every directory, aside from the root directory, has a parent directory.

Special Files: Character device and Block device file

• Hard drives, printers, displays, terminal emulators, and CD/DVD drives are just a few examples of the hardware devices that Linux handles as unique files.
• To expose the device as a file in the file system is the goal of a special file.
• Because tools for file I/O may access the device, a particular file offers a universal interface for physical devices (including virtual devices produced and utilised by the kernel).
• Data written to or read from a special file occurs instantly and is not governed by standard filesystem conventions. 
• A character special file is an example of a device, like a printer or monitor, that sends data in bytes. A block special file is an example of a device, like a hard disc, that transmits data in blocks.
• a block-specific special file that grants access to a device that sends data in fixed-size groups. As an instance, a disc.
• a unique character file that grants access to a device—like a terminal—that sends data in single-character increments.

Link files: Hard link And Soft links

• We can utilise a file from a different place and with a different filename thanks to link files. Link files are used for this.
• A pointer to another file is found in a link file. connections come in two varieties: symbolic or soft connections and hard linkages.
• The original file is mirrored when a hard link is used.
• You cannot make a hard link to a file or directory on a different filesystem.#
• By name, a symbolic or "soft" link refers to a specific file.
• It is possible to make a soft link to a file or directory on a different filesystem.

Socket Files:

• Applications utilise sockets as communication endpoints to share data.
• For instance, a programme on the local system connects to the socket of a distant application using the port number and IP address of the remote application in order to interact with it.
• Sockets are used by all programmes that accept connections from distant clients or other applications.
• Every socket has a port number and IP address that enable it to receive connections from clients.
• Linux employs socket files to facilitate communication between local programmes.

• Applications running on the local system can communicate data using socket files without requiring the complicated networking and sockets procedure.
• The unique files known as socket files are those that refer to themselves by their file name rather than by their IP address and port number.
• The sendmsg() and recvmsg() system functions are used by socket files to provide inter-process communication between nearby programmes.

Named Pipes:

• Named pipes facilitate communication between two processes that are operating on the same host, much as local domain sockets.
• Another name for them is "FIFO files."
• Mknod can be used to build named pipes, while rm may be used to delete them.
• The functions of named pipes and local domain sockets are identical, and their existence is largely an artefact of the past.
• If UNIX and Linux were created today, network sockets would probably be used in place of both of them.