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Part One

Part One. The Essence of UNIX. Overview. Unix history Origins, versions, distributions Using Unix Log in/out Unix shells Basic commands Editor(s) Compile a C/C++ program. Introducing the UNIX Operating System. UNIX is a multi-user system

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Part One

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  1. Part One The Essence of UNIX

  2. Overview • Unix history • Origins, versions, distributions • Using Unix • Log in/out • Unix shells • Basic commands • Editor(s) • Compile a C/C++ program

  3. Introducing the UNIXOperating System • UNIX is a multi-user system • Allows many users access and share the resources of a server computer • UNIX is a multitasking system • Allows user to execute more than one program at a time • UNIX is a portable operating system • Used in many computing environments

  4. Unix History • Bell Labs … • UC Berkeley … • Commercial versions: • Solaris, Irix, HP/UX, Ultrix, SCO Unix, AIX, … • Open source versions: • FreeBSD • Linux

  5. Linux and UNIX • Linux is UNIX-like • Created by Linus Torvalds • Not written from traditional UNIX code • Linux is original code • follows POSIX standards

  6. Linux Structure

  7. Linux Distributions • Many companies have createdLinux distributions • distributions contain • source code for the Linux kernel and utilities • installation tools • professional documentation • technical support, • specialized software • They can charge as much as they choose for their Linux distributions

  8. Linux Distributions

  9. UNIX Concepts • Shell • The interface between user and OS • Hierarchical Structure • Directory and subdirectory organization • Layered components • Layers of software cover hardware

  10. Choosing Your Shell • Shells interpret commands and act as first-class programming language • A default shell is associated with your account when created • A list of some UNIX shells: • Bourne • C shell • Korn • Bash, tcsh

  11. Choosing User Names and Passwords • To use UNIX, a user must log in by providing a unique user name and password • UNIX system administrators create accounts by adding user names and passwords

  12. Connecting to a UNIX System • Directly via attached terminal • Via terminal window in windowing system • Remotely through telnet, rsh or ssh

  13. Connecting to UNIXUsing Telnet • telnet is terminal emulation software • Deemed insecure • Better: ssh • connects to Unix server • Once connected to a UNIX host, work with UNIX may begin • Uses IP addresses or domain names to access remote systems

  14. Entering Commands • To interact with UNIX, a command is entered at the command prompt • UNIX is case-sensitive and most commands are typed in lower case • Two categories of commands • User-level: perform tasks • System administration: system management

  15. Entering Commands • The date command • Displays the system date, which the system administrator maintains • The cal command • Shows the system calendar • The who command • Shows who is using the system and their current location

  16. Entering Commands

  17. Entering Commands

  18. Entering Commands

  19. Entering Commands • Command-line editing (shell dependent) • Certain keystrokes perform command-line editing • Use up and down arrow keys to scroll through command history • Multiple command entry • Separate commands with semicolon(;) • The clear command • Clears the current screen

  20. Getting Help The man program displays the UNIX online reference manual, called the man pages, for help purposes

  21. Viewing Files • Use cat, more, and less to view an entire file contents • cat displays a whole file at one time • more displays a file one screen at a time, allowing scroll down • less displays a file one screen at a time, allowing scroll down and up

  22. Viewing Files • Use head and tail to view the first few or last few lines of a file • head displays the first few lines • tail displays the last few lines

  23. Logging Out of UNIX • Logging out ends your current process and indicates to UNIX that you are finished • Logging out is shell dependent • Bourne, Korn, Bash – exit command • C shell – logout command

  24. Changing Passwords • For security purposes, changing passwords is necessary • Use the passwd command • UNIX allows new password if: • The new password differs by at least three characters • It has six or more characters, including at least two letters and one number • It is different from the user name

  25. Understanding the Role of the UNIX System Administrator • User “root” manages the UNIX system • Adds users and deletes old accounts • Also called the superuser • Unlimited permission to alter system

  26. Unix file system

  27. Understanding the UNIXFile System • A file is the basic component for data storage • UNIX considers everything it interacts with a file • A file system is UNIX’s way of organizing files on mass storage (disk) devices • A physical file system is a section of the hard disk that has been formatted to hold files • The file system is organized in a hierarchical structure similar to an inverted tree

  28. Understanding the Standard Tree Structure • The structure starts at the root level • Root is the name of the file at this basic level and it is denoted by the slash character (/) • A directory is a file that can contain other files and directories • A subdirectory is a directory within a directory • The subdirectory is considered the child of the parent directory

  29. Exploring the Root File System • UNIX must mount a file system before any programs can access files on it • To mount a file system is to connect it to the directory tree structure • The root file system is mounted by the kernel when the system starts

  30. Exploring the Root File System • The root directory contains sub-directories that contain files: • /bin contains binaries, or executables needed to start the system and perform system tasks • /boot contains files needed by the bootstrap loader as well as kernel images • /dev contains system device reference files

  31. Exploring the Root File System • Root subdirectories continued: • /etc contains configuration files that the system uses when the computer starts • /lib contains kernel modules, security information, and the shared library images • /mnt contains mount points for temporary mounts by the system administrator • /proc is a virtual file system allocated in memory only

  32. Exploring the Root File System • Root subdirectories continued: • /root is the home directory of the root user, or the system administrator • /sbin contains essential network programs used only by the system administrator • /tmp is a temporary place to store data during processing cycles • /var contains subdirectories which have sizes that often change, such as error logs

  33. Understanding Pathsand Pathnames • To specify a file or directory, use its pathname, which follows the branches of the file system to the desired file • A forward slash (/) separates each directory name • The UNIX command prompt may indicate your location within the file system • Use the UNIX pwd command to display the current path name

  34. Navigating the File System • To navigate the UNIX directory structure, use the cd (change directory) command • UNIX refers to a path as either: • Absolute - begins at the root level and lists all subdirectories to the destination file • Relative - begins at your current working directory and proceeds from there

  35. Listing Directory Contents The ls (list) command displays a directory’s contents, including files and subdirectories

  36. Listing Directory Contents • ls options: • a include files with “.” • l long format • R recursively list subdirectories

  37. Listing Directory Contents

  38. Managing Directories and Files • mkdir (make directory) command • Create a new directory • rmdir (make directory) command • Delete an empty directory • cp (copy) command • Copy files from one director to another • rm (remove) command • Delete files

  39. Setting File Permissions

  40. Setting File Permissions

  41. Setting File Permissionsfor Security • chmod command • To set file permissions • Settings are read (r), write (w), execute (x) • The three types of users are owners, groups, and others • Setting permissions to directories • Use the execute (x) to grant access

  42. Using Input and Error Redirection • You can use redirection operators to retrieve input from something other than the standard input device and send output to something other than the standard output device • Examples of redirection: • Redirect the ls command output to a file, instead of to the monitor (or screen) • Redirect a program that receives input from the keyboard to receive input from a file instead • Redirect error messages to files, instead of to the screen by default

  43. Redirecting Output • The greater than sign (>) is called a redirection symbol • Create a new file or overwrite an existing file by attaching (>) to a command that produces output • To append to an existing file, use two redirection symbols (>>)

  44. Creating new files • using cat output redirection • concatenate text via output redirection • touch command on new file • invoke editor for new file

  45. Manipulating Files • Delete files when you no longer needed • rm command • permanently removes a file or an empty directory • -r option removes a directory and everything it contains • Copy files as a means of back-up or as a means to assist with new file creation • cp command • copies the file(s) specified by the source path to the location specified by the destination path

  46. Manipulating Files • Moving a file • mv command • removes file from one directory and places it in another • Finding a file helps you locate it in the directory structure • find command • searches for the file that has the name you specify

  47. Manipulating Files • Combining files using output redirection • cat command • concatenate text of two different files via output redirection • paste command • joins text of different files in side by side fashion • Extracting fields of a file using output redirection • cut command • removes specific columns or fields from a file

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