Unix file system explained

These files are used to store information of the users. It may be some text or any image which is stored. It is normally located under a directory and does not contain any other files. Directories help in organizing the files which are present. The directories can contain ordinary files, special files or even other directories. All these directories are the descendants of the root directory.

The special files are used to represent physical devices like printer, tape driver or a terminal. Unix considers any device to be a file. Even the terminal is considered to be a file. It is considered as standard input file from where input is read. To link commands Unix provides pipes. The pipe is a temporary file. This also holds data from one command which is kept until it is read by another command. The output of one command is given to the next command as an input.

There is clear segregation between the contents of the file and the information which is present in the file. All files consist of a sequence of characters except for the device and special files. The information which is needed in the filesystem to handle the files is included in a data structure which is called inode. The inode is used to identify a file.

A few attributes must be provided to handle the kernel and filesystem functions. File ownership is an important component of Unix that provides a secure method for storing files. Here, the first column represents different access modes, i. The first three characters represent the permissions for the file's owner. For example, -rwxr-xr-- represents that the owner has read r , write w and execute x permission. The second group of three characters consists of the permissions for the group to which the file belongs.

For example, -rwxr-xr-- represents that the group has read r and execute x permission, but no write permission. The last group of three characters represents the permissions for everyone else. For example, -rwxr-xr-- represents that there is read r only permission.

The permissions of a file are the first line of defense in the security of a Unix system. Directory access modes are listed and organized in the same manner as any other file.

Access to a directory means that the user can read the contents. The user can look at the filenames inside the directory. A user must have execute access to the bin directory in order to execute the ls or the cd command. To change the file or the directory permissions, you use the chmod change mode command. There are two ways to use chmod — the symbolic mode and the absolute mode. Such a case could occur, for example, if a hard disk drive suffers physical failures and cannot be properly mounted.

Many systems clear this directory upon startup; it might have tmpfs mounted atop it, in which case its contents do not survive a reboot, or it might be explicitly cleared by a startup script at boot time. Users other than root can access their own mail only. Contains print jobs, mail spools and other queued tasks.

Ordinary files — An ordinary file is a file on the system that contains data, text, or program instructions. Used to store your information, such as some text you have written or an image you have drawn. This is the type of file that you usually work with. Do not contain other files. Directories — Directories store both special and ordinary files. A directory file contains an entry for every file and subdirectory that it houses. If you have 10 files in a directory, there will be 10 entries in the directory.

Each entry has two components. They appear in a file system just like an ordinary file or a directory. This type of access is called raw device access. This type of access is called block device access. For disk devices though, raw access means reading or writing in whole chunks of data — blocks, which are native to your disk.