Introduction to Computing

Transcription

1 Chapter 1 Introduction to Computing Unix is an operating system. In a unix environment, the fundamental layer is the hardware which provides the service the users need. The hardware include the CPU, memory, disk and many other parts that are necessary for computing. The operating system is referred as kernel which takes care of the technical aspects of the computer s operation. The users do not need to know anything about the configuration of the hardware. They may request services such as printing. The operating system will direct the hardware to perform those tasks. In order to achieve this goal, the user programs provide a set of commands (system calls). These commands will request actions from the kernel to perform certain task such file management or run a program. Unix is a multi-user, multi-tasking operating system. They are many users logged into a system simultaneously, each running his or her own programs. The role of the kernel b to keep each process and user separate and to regulate access to system hardware, including cpu, memory, disk and other I/O devices. 1.1 Introduction to Unix The Unix structure can be represented as a inverted tree structure with the root on top. Programs are sorted and stored into different places which are called directories. The programs are accessible to all users. But only the system administrators have 1

2 2 CHAPTER 1. INTRODUCTION TO COMPUTING the authority to change some important features or aspects of the entire system Log On/Off It should always noted that the Unix system is shared by many users and many programs. Each user has a unique ID and a corresponding password. For security reason, the password should be reasonably complicated. You should use your first name or last as the password. It is recommended not to use a single word as the password. Also, you should change your password periodically. After you have done your work, you should always log off to protect your work. 1.2 File Management Your files will be placed in a directory that has been assigned to you by the system. You have the permission to create, copy and delete your files in your own directory. There are mainly two types of files: directories and files File Creation There are many text editor available. The most powerful one is probably a program called vi. It is a bit difficult to use it at the first place but it can perform many operations. There are other editors such as nedit which is much more user-friendly. To create a directory, you use the following $ mkdir directory-name Check the files To list the files, one use the following command: $ ls or

3 1.3. FILE TYPES 3 $ ls -l If there are too may files, one can list a certain group. For example: $ ls a* or $ ls *.txt 1.3 File Types There are many types of files in Unix System Files The system files are usually started with a dot, for example.cshrc or.plan. These files defines the environment of your account. YOU SHOULD NOT MODIFY OR DELETE THESE FILES Directories The directories are containers that are used to store more than one file. The name of directories should be informative instead of using some generic names such T or U. 1.4 Commonly used files File identification consists of two parts: file name given by the user and extension. The first part is given by the user and the second part indicates the actual type of one particular file. 1. Data files usually have the extension.dat or.txt. 2. Files containing computer source code have extension such as.c or.f.

4 4 CHAPTER 1. INTRODUCTION TO COMPUTING 3. Web files have extensions.html or.htm. 4. Acrobat files ends with.pdf. 5. Image files ends with.gif or.jpeg or.ps. 6. Latex files:.tex and.dvi. 7. Files without extension might be programs that can be executed by the user.

5 1.5. FILE PERMISSIONS File Permissions If one list the files under his or her own account using $ ls -l One may find that the following shown on the screen: drwxrwxr-x 2 abc 1024 Aug 29 22:58 Assigment/ -rwxr-xr-x 1 abc 359 Aug 29 23:05 grades* -rw-r--r-- 1 abc 1381 Aug 29 22:59 problem_set_1.txt If you set up your website and see an error such as F ilenotf ound, you should check the file permission if the files does exist in the tartget directory. To grant the permission of a file or directory $ chmod a+rx *. To remove the access by other users, one can use the following command: $ chmod a-rx *. To make sure that you own the files, you might try $ chmod 700 *.

6 6 CHAPTER 1. INTRODUCTION TO COMPUTING 1.6 Copy and Remove Files To copy a file to one location to another, one can use the following $ cp grades.txt Answers where Answers is a directory. To copy the file to the root of your account, one might use $ cp grades.txt To remove a file, the command is $ rm grades.txt To remove a directory, the command is $ rmdir Directory-name while all the files within that directory have to be removed. To remove everything under one directory, the command is $ rm -r Directory-name This will delete recursively all the files and sub-directories under the target directory Directories To access one sub-directory under the current directory, the command is $ cd Directory-name To go back one level, the command is $ cd.. To go back to the root directory in one command, one might simply use $ cd 1.7 File Transfer In order to transfer files from one machine to another, you need to use FTP or WSFTP which is window-based program to transfer files. To use FTP to transfer files manually, you need to type

7 1.8. PRINTING 7 f tpdestination Then you need to type your user name and password. To obtain a file from the above location, you need to use getfile name To make a copy of the file in your current directory, you need to use putfile name PROBLEM SHOOTING: [1] Pay attention to put and get [2] Set the BINARY mode ftp > bin [3] Pay attention to permission 1.8 Printing PDF or image files such as.pdf.gif or.jpeg can not be printed directly. Software must be used to handle them. Postscript files (.ps) can be printed directly.

8 8 CHAPTER 1. INTRODUCTION TO COMPUTING 1.9 TIPS Getting Help $ man command Process Control $ ps -u user-name It would be good to run one job at a time instead of running multiple tasks at the same time. You should choose a less busy time to run a time-consuming task Always Make Copies You can make copies of your files. fold is a very way of making things organized File Organization To be efficient, you need to organize your files like your home.