Inside Linux

 Inside Linux

• Kernel  

1.  The core of the UNIX system. Loaded at system start up (boot). Memory-resident control program. 
2.  Manages the entire resources of the system, presenting them to you and every other user as a coherent
3.  system. Provides service to user applications such as device management, process scheduling, etc. 
4. Example functions performed by the kernel are: 

                ⦾  Managing the machine's memory and allocating it to each process.

                ⦾  Scheduling the work done by the CPU so that the work of each user is carried out as efficiently as is possible.

                ⦾  Accomplishing the transfer of data from one part of the machine to another

                ⦾  Interpreting and executing instructions from the shell

                ⦾  Enforcing file access permissions

       

      5. You do not need to know anything about the kernel in order to use a UNIX system. These details are provided for your information only.

•  Shell  

1. Whenever you login to a Unix system you are placed in a shell program. The shell's prompt is usually visible at the cursor's position on your screen. To get your work done, you enter commands at this prompt. 
2. The shell is a command interpreter; it takes each command and passes it to the operating system kernel to be acted upon. It then displays the results of this operation on your screen.
3.   Several shells are usually available on any UNIX system, each with its own strengths and weaknesses.
4. Different users may use different shells. Initially, your system adminstrator will supply a default shell, which can be overridden or changed. The most commonly available shells are:  

                    ⦾  Bourne shell (sh)

                    ⦾  C shell (csh)

                    ⦾  Korn shell (ksh)

                    ⦾  TC Shell (tcsh)

                    ⦾  Bourne Again Shell (bash)

      5. Each shell also includes its own programming language. Command files, called "shell scripts" are used to accomplish a series of tasks.

• Utilities

1. UNIX provides several hundred utility programs, often referred to as commands.
2. Accomplish universal functions

                    ⦾  editing

                    ⦾  file maintenance

                    ⦾  printing

                    ⦾  sorting

                    ⦾  programming support

                    ⦾  online info etc.

      3. Modular: single functions can be grouped to perform more complex tasks