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					 Introduction to UNIX


                 Ke Liu
http://www.cs.binghamton.edu/~kliu/cs350/
         Kliu1@binghamton.edu




                                            1
                   Topics.
•   Logging in.
•   Unix Shells and useful shell commands.
•   File System in Unix.
•   Program, Process and Process control.
•   Inter-process communication.
•   Compiling and debugging C programs.
•   Editors.
                                             2
                  UNIX
• UNIX is multi-user and multi-tasking
  operating system.
• Multi-tasking: Multiple processes can run
  concurrently.
• Example, different users can read mails,
  copy files, and print all at once.


                                              3
               Logging In
• Enter login name and password !
• System password file: /etc/passwd (usually).
• You can change password using the
  command: passwd.




                                             4
                    Shell
• After a successful login, the shell program
  is run. The default shell of bingsuns: tcsh
• bingsun2% ps
  PID TTY TIME CMD
  2159 pts/2 0:00 tcsh
• Shell is a command line interpreter that
  reads user commands and executes them.

                                                5
               Unix Shells
• Common Shells: Bourne shell, the C shell,
  and the Korn shell.
• The shell on bingsuns is tcsh (tc shell).
• Users can switch between shells, using the
  commands bash, csh, ksh, sh.
• Control D (^d) to return back to original
  shell, or just use the command: exit.

                                               6
      Some shell commands
• Most Important command: man (manual
  pages).
• Help: unix commands, C functions.
• Usage: man <command/function>
• Try “man man” !
• Example:
  man ls, man passwd, man printf.
                                        7
    Some shell commands (cont’)
• pwd: working directory (/u0/users/2/kliu1).
• ls: list contents of directory
• mkdir <dir-name>: make directory
• rmdir <dir-name>: remove an empty directory
• rm –r <dir-name>: remove a directory with all the
  contents
• cd <directory>: change directory, ~/ means your
  home directory
• cp <source> <target>: copy command.
                                                      8
   Some shell commands (cont’)
• chmod <mode> <filename>: change mode of a
  file/directory
• ls –l <directory or filename>: long list with details
• 9 permission bits: d r w x r w x r w x
• 3 categories: user/group/all.
• Permissions: read/write/execute (r/w/x).
• E.g.: mode= 644 means r w _ r_ _ r _ _
  command: chmod 644 <filename>
• first 3 bits for user. Next group. Next all others.
                                                      9
  Some shell commands (cont’)
• rm <option> <filename>: remove files
  e.g.: rm –fr directory/filename
• mv <old> <new>: change the name of a file
• Pipes: Connect the stdout of one command
  with the stdin of another command
   e.g.: ls -l | more or ls –l | less

                                          10
                 File System
• Hierarchical arrangement of files and directories.
• Top level: root or /
  e.g.: cd /
• . Current directory, .. One level higher directory
  e.g.: cd . No change for it is current directory
  or cd .. Change to parent directory.


                                                       11
         File System (cont’)
• Pathname: absolute and relative.
• Absolute pathname: /u0/users/2/kliu1
• Relative pathname: abc.




                                         12
                    Editors.
•   Different editors: emacs, pico, vi
•   emacs <filename>
•   pico <filename>
•   vi <filename>




                                         13
    The easiest editor: pico or nano
•   pico <filename>
•   Full screen editor
•   Help on the bottom of the screen
•   The nano is an extension to the pico




                                           14
         Basic operations in pico
•   Ctrl + v : to move page down
•   Ctrl + y : to move page up
•   Ctrl + o : to save the current buffer
•   Ctrl + x : to exit with or without saving
•   Ctrl + g : to get help
•   Ctrl + r : to open a file
•   Ctrl + w : to find a string in the current buffer
•   Ctrl + c : to get the current position in the buffer
                                                           15
          Program & Process
• Program is an executable file that resides on
  the disk.
• Process is an executing instance of a
  program.
• A Unix process is identified by a unique
  non-negative integer called the process ID.
• Check process status using the “ps”
  command.
                                              16
      Foreground/background
            processes
• A program run using the ampersand
  operator “&” creates a background process.
• E.g.:
  bingsun2% back &
• otherwise it creates a foreground process.
• E.g.:
  bingsun2% back
                                           17
       Foreground/background
             processes
• Only 1 foreground process for each session.
  Multiple background processes.
• Where are background processes used?
• All system daemons, long user processes, etc.
  e.g. printer-daemon process or mailer-daemon
  process.
• These processes are always running in background.
• Pine is foreground process.
                                                 18
            Process Status
bingsun2% back &
[1] 16488 the process id assigned by system
bingsun2% ps
  PID TTY TIME CMD
  1973 pts/39 0:01 tcsh
 16488 pts/39 0:00 back

                                              19
         How to stop a process?
• Foreground processes can generally be stopped by pressing
  CONTROL C (^C).
• Background processes can be stopped using the kill
  command.
• Usage: kill SIGNAL <process id list>
• kill -9 <process id list> (-9 means no blocked)
   Or kill <process id list>.
• If a foreground process is not stopping by ^C, you can
  open another session and use the kill command.

                                                         20

				
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