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Monday, 7 August 2017

Linux file system - Shell scripts,Files,Kernel

Linux File System

linux file system
Linux File System


A file system is a method of storing and organising arbitrary collects of data in a form that is human-readable. A file system organizes data into an easy to manipulate database of human readable names for the data ,usually with a human readable hierarchical organization of the data ,for the storage ,organisation ,manipulation and retrieval by the computer OS (operating system). Each discrete collection of data in a file system is referred to as a computer.File system are used on data storage devices such as hard disk -CD ROMs to maintain the physical location of the files.

The linux system contains thousands of files located within many directories.

The "trunk" of the tree is the root directory.
The root directory is simply identified as a"/".
All other directories "branch" Off from the trunk.
The tree of the file system starts at the trunk or slash, indicated by a forward slash (). This directory ,containing all underlying directories and files is also called the root directory or the "root" of file system.

Directories that are only one level below the root directory are often preceded by a slash ,to indicate their position and prevent confusion with others directories that could have the same name. When starting with a new system ,it is always a good idea to take a look in the root directory.

the following lists the most common directories and their intended contents.

 / - root directory.
/home - where directories are contained for each other.
/usr - pronounced 'user' and contains Linux commands and utilities.
/bin - binary executable programs.
/lib - program libraries ,similar to windows 'dll' files
/sbin - move executable programs and linux utilities for administrative purpose.
/doc - documentation
/src - source code to programs
/tmp - temporary code to programs.
/etc - configuration files.
/rc.d - scripts used during boot and shutdown process.
/sysconfig - default.
/sysconfig/network scripts - network scripts
/sysconfig/daemons - special programs that run in background ,such as print spooling.
/bin - binary executable programs that all users need.
/dev - device files that control drives ,terminal and any equipment attached to the server.
/var - user specific files.
/log - files containing system usage and errors
/spool where spooled files are stored during print spooling process
/mail - where Email files are stored until retrieved by client Email program
/proc -system files.
/root - root's home directory
opt - others options
/sbin - more executable program and utilities.

Important files and Directories 

The Kernel is the core of any operating system. The source code is not freely available for any of the commercial versions of UNIX. quite the opposite exists for linux. As such, procedures for compiling and patching kernels and drives are vastly different. with linux and other open source operating systems ,a patch can be released in source code form and end users can install it or even verify and modify it if desired.These patches tend to be far less tested than patches from UNIX vendors. Since there  is not a complete list of applications and environments that need to be tested on linux, the linux developers have to depend on many eyes of end users and other developers to catch bugs. Commercial UNIX vendors  only release their kernels in binary form. If an update is required ,the administrator has to wait for the vendors release the patch in binary form  but they required, the administrator has to wait for vendor has performed sufficient regression testing.

The Shell is a UNIX term for the interactive users interface with an operating system. The shell is the layers of programming that understands and executes the commands a users enters. In some systems ,the shell is called a command interpreter.
Shell is a software program that allows you to interact and access a computer system. User can enter commands in the shell prompt, which will be executed by the shell. Since the only means of communication through shell is test ,it is known as Command-Line-Interface or CLI.

Types of Shell - there are different types of shells in Linux and UNIX each shell work  is different from each other-

  • sh or Bourne Shell : This shell is used in UNIX and in Unix related environments.Sh shell is basic shell and has a few features.

  • bash or bourne again shell : It is a standard GNU shell, Intuitive and flexible. Probably tool the most advisable for beginning users while being at the same time a powerful tool for the advisable for beginning users while being at the same time a powerful tool for the advanced and professional user. On Linux ,bash is the standard shell for common users. This shell is so-called superset of the bourne shell, a set add-ons  and plug-ins. This means that the bourne again shell is compatible with the bourne shell ; commands that work in sh, also work in bash.

  • csh or C shell : this shell is used for C programming.

  • tcsh or TENEX C shell : this is a advanced version of c shell and it is also called TURBO C.

  • ksh or the Korn Shell : Sometimes appreciated by people with UNIX background. A superset of the bourne shell ; with standard configuration a nightmare for beginning users.



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