BIL 101E Introduction to Computers and Information Systems

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BIL 101EIntroduction to Computers and
Information Systems

• Spring 2006

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Unix History

• The unfinished development of OS Multics at
  Bell Laboratories in 1965 left them without a
  good OS.
• Ken Thopson and Dennis Ritchie decided to
  sketch out an OS for BL.
• Ken Thompson implemented it on PDP-7. As a pun
  on Multix he named the new operating system Unix.
  
• A new programming language C was developed for
  implementation of Unix and 95 of this operating
  system was written in C - therefore Unix is a
  very good portable system.

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Linux History

• Linux was written by Linus Torvalds and has been
  improoved by countless number of people around
  the word.
• It was initially developed for small PC.

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Linux Features
multitasking several programs running at once
multiusers several users at the same machine
at once multiplatforms it runs on many
different CPU
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Getting Started

• You can login to an UNIX operating system after
  you had been assigned a username by a system
  administrator.
• login
• Unix/Linux is case sensitive (as the C language).
  Username smith is different from Smith
• After entering your username you will be faced
  with the following
• password

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Getting Started

• If you have typed your password correctly a
  prompt will appear. For example
• or a little detailed prompt
• marian

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UNIX DIRECTORY STRUCTURE

• In Unix, the files are organized into a tree
  structure with a root named by the character '/'.
  The first few levels of the tree look like this

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UNIX DIRECTORY STRUCTURE

• In many systems the user files are subdirectories
  of a
• directory named home' in root directory /. If
  we had
• a user tango, for example, tangos home directory
  
• would be /home/tango, and all his files would be
• within that subtree.
• Suppose tango's directory looks like this

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UNIX DIRECTORY STRUCTURE
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FILE TYPES
There are four types of files in the Unix file
system. Ordinary Files An ordinary file may
contain text, a program, or other data. It can
be either an ASCII file, with each of its bytes
being in the numerical range 0 to 127, i.e. in
the 7-bit range, or a binary file, whose bytes
can be of all possible values 0 to 255, in the
8-bit range.
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FILE TYPES

• Directory Files
• Suppose that in the directory x I have a, b and
  c,
• and that b is a directory, containing files u and
  v.
• Then b can be viewed not only as a directory,
• containing further files, but also as a file
  itself.
• The file b consists of information about the
  directory b
• i.e. the file b has information stating that the
• directory b has files u and v, how large they
  are,
• when they were last modified, etc.

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FILE TYPES

• Device Files
• In Unix, physical devices (printers,
  terminals etc.) are represented as files.
• This seems odd at first, but it really makes
  sense This way, the same read() and write()
  functions used to read and write real files can
  also be used to read from and write to these
  devices.

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FILE TYPES

• Link Files
• Suppose we have a file X, and type
• ln X Y
• If we then run ls, it will appear that a new
  file, Y, has been created, as a copy of X, as if
  we had typed
• cp X Y
• However, the difference is the cp does create a
  new file, while ln merely gives an alternate name
  to an old file. If we make Y using ln, then Y is
  merely a new name for the same physical file X.

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Listing Files

• The a' (all'') and l' (long'') options of
  the ls command will give us a lot of information
  about files in a specified directory.
• ls al
• drwx--x--x 63 tango users 4096 Sep
  17 0133 .drwxr-xr-x 7 root root
  4096 Sep 3 1653 ..drwxr-xr-x 30
  tango users 4096 Sep 15 1144
  downloadsdrwxr-xr-x 4 tango users
  4096 Jul 25 2319 evrimdrwxr-xr-x 5
  tango users 4096 Sep 17 0053 foy
• 1st column - access permissions (see below)
• 2nd column - number of file entries (in the case
  of directory files)
• 3rd column - owner
• 4rd column group
• 5th column - size in bytes
• 6th column - date and time of last modification
• 7th column - name

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File Permissions

• In Unix, all files are protected under some
  access control mechanism, so that the owner of a
  file can deny access of his files to other users.
  The first column of the long directory list shows
  the access characteristics of a file, in te form
  of 10 flags, e.g.
• drwxr-xr-x.
• Position 1 file type d (directory)
  
• - (ordinary file)
  
• l (symbolic
  link)
• Position 2-4 permissions for the owner
• r (read), w (write) , x (execute)
• Position 5-7 permissions for other users in
  the same group
• Position 8-10 permissions for all other users

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BASIC UNIX COMMANDS

• The command line is a place where the commands of
  a operating system are called and the results of
  the commands are seen.
• The commands are the tools that the operations
  needed by the user to operate the system.
• The basic commands about basic operations, disk
  operations, administrative or user based
  operations, network operations are given here.
• Please note that this is not a complete set of
  commands, but most commonly used ones are
  documented here.

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BASIC UNIX COMMANDS
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BASIC UNIX COMMANDS

• ls Lists contents of directories. Directory
  contents are sorted alphabetically.
• l In addition to the name of each file,
  prints the file type, permissions, number of hard
  links, owner name, group name, size in bytes, and
  timestamp (the modification time).
• a Lists all files in directories, including all
  files that start with ..
• --color Controls whether color is used to
  distinguish file types.
• ls l
• ls a
• ls al
• ls color

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BASIC UNIX COMMANDS

• man Formats and displays the online manual
  pages. To exit the manual pages q character
  should be used.
• man ls
• cd Change directory command allows you to
  change the present working directory to another
  one.
• cd /home/user1/examples
• cd ..
• cd ../../
• cd ../../ex/project

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BASIC UNIX COMMANDS

• mkdir Creates a new directory with each given
  name.
• mkdir bil101
• rm Removes files or directories. By default, it
  does not remove directories.
• -f Ignores nonexistent files, never prompt
• -i Prompts before any removal
• -r, -R Removes the contents of directories
  
• recursively.

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BASIC UNIX COMMANDS

• rm ex1
• rm .c
• rm .
• rm f .c
• rm i example1
• rm r /home/user2/abc/

rmdir Removes empty directories. rmdir cse100
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BASIC UNIX COMMANDS

• cp Copies files and directories. If the last
  argument names an existing directory, cp copies
  each other given file into a file with the same
  name in that directory. Otherwise, if only two
  files are given, it copies the first onto the
  second. It is an error if more than two files are
  given. By default, it does not copy directories.
• i Prompts whether to overwrite existing regular
  destination files.
• R Copies directories recursively.
• cp ex1.c ex2.c
• cp ex1.c exs/
• cp ex1.c exs/ex2.c
• cp i ex1.c ../exs/
• cp R exs/ ../examples/

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BASIC UNIX COMMANDS

• mv Moves (renames) files. If the last argument
  names an existing directory, mv moves each other
  given file into a file with the same name in that
  directory. Otherwise, if only two files are
  given, it moves the first onto the second. It
  also renames directories.
• mv ex1.c ex2.c
• mv ex1.c ../exs/ex2.c

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BASIC UNIX COMMANDS

• mdir Displays an MSDOS directory. If your floppy
  disk is DOS-formatted, then you can see the
  content of your floppy disk by typing
• mdir a
• mcopy Copies MSDOS files to/from Unix. If your
  floppy disk is DOS-formatted, then you can copy
  your files from the floopy disk to the harddisk
  or from the harddisk to the floppy disk without
  mounting it.
• mcopy ex1.c a.
• mcopy aex2.c .
• mcopy ex1.c aex2.c
• mcopy aex2.c ex3.c

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BASIC UNIX COMMANDS

• mmd Makes an MSDOS subdirectory. If your floppy
  disk is DOS-formatted, then you can create
  directory in your floppy disk.
• mmd dir1
• mrd Removes an MSDOS subdirectory. If your
  floppy disk is DOS-formatted, then you can remove
  a directory in your floppy disk.
• mrd dir1
• mcd Changes MSDOS directory. If your floppy
  disk is DOS-formatted, then you can change
  directory in the floopy disk.
• mcd dir2

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BASIC UNIX COMMANDS

• mdel Deletes an MSDOS file. If your floppy disk
  is DOS-formatted, then you can delete a file in
  your floppy disk.
• mdel ex2.c
• fdformat fdformat does a low level format on a
  floppy disk. Device is usually one of the
  following
• fdformat /dev/fd0H1440
• mformat Adds an MSDOS filesystem to a low-level
  formatted floppy disk.
• mformat a

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BASIC UNIX COMMANDS

• pwd Prints name of the current working
  directory.
• pwd
• find Searches for files in a directory
  hierarchy. find searches the directory tree
  rooted at each given pathname by evaluating the
  given expression from left to right, according to
  the rules of precedence, until the outcome is
  known, at which point find moves on to the next
  pathname.
• name pattern Base of the path matches shell
  pattern
• find / -name .c
• find ./ -name .c
• find /home/user2/ -name .c

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BASIC UNIX COMMANDS

• cat Concatenates files and prints on the
  standard output.
• cat ex3.
• cat ex2.c ex5.c
• cat ex4.c ex3.c gt ex5.
• more more is a filter for paging through text
  one screenful
• at a time.
• ls more
• less Less is a program similar to more, but
  which allows
• backward movement in the file as well as forward
  movement.
• ls less

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BASIC UNIX COMMANDS

• chmod Changes the permissions of each given
  file according to mode, which can be either a
  symbolic representation of changes to make, or
  an octal number representing the bit pattern
  for the new permissions.
• In the symbolic mode a combination of the
  letters ugoa controls which users' access to
  the file will be changed the user who owns it
  (u), other users in the file's group (g), other
  users not in the file's group (o), or all users
  (a). The operator causes the permissions
  selected to be added to the existing permissions
  of each file - causes them to be removed. The
  letters rwx select the new permissions for the
  affected users read (r), write (w), execute(or
  access for directories) (x).
• chmod uw ex3.c
• chmod a-x ex5.c

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BASIC UNIX COMMANDS

• A numeric mode is from one to four octal
  digits(0-7), derived by adding
• up the bits with values 4, 2, and 1. Any omitted
  digits are assumed to
• be leading zeros. The first digit selects the
  set user ID (4) and set
• group ID (2) and save text image (1) attributes.
  The second digit
• selects permissions for the user who owns the
  file read (4), write (2),
• and execute (1) the third selects permissions
  for other users in the
• file's group, with the same values and the
  fourth for other users not in
• the filess group, with the same values.
• -R change files and directories recursively
• chmod 755 ex2.c

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BASIC UNIX COMMANDS
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BASIC UNIX COMMANDS

• chown Changes file owner and group.
• -R operate on files and directories recursively
• chown user3 ex3.c
• chown R user4 examples/
• chown user3.user3 ex4.c
• chgrp Changes group ownership.
• -R operate on files and directories recursively
• chgrp user5 ex6.c
• chgrp R user6 examples/a

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BASIC UNIX COMMANDS

• du Estimates file space usage
• du exs/
• gzip Compresses files.
• -c Write output on standard output keep
  original files unchanged.
• gzip c final/ gt fin.gz
• gunzip Expands files. gunzip can decompress
  files created by gzip.
• -c Write output on standard output keep
  original files unchanged.
• gunzip c fin.gz

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BASIC UNIX COMMANDS

• tar It is an archiving program designed to store
  and extract files from an archive file.
• -c create a new archive
• -f use archive file
• -z filter the archive through gzip
• -v verbosely list files processed
• -x extract files from an archive
• tar cvfz str.tgz /home/user1/
• tar xvfz str.tgz
• paswd Updates a user's authentication tokens
• passwd
• passwd user5
• whoami Prints the user name associated with the
  current effective user id.
• whoami

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BASIC UNIX COMMANDS

• ps Reports process status. Ps gives a snapshot
  of the current processes. It returns the process
  id knowledge.
• -A select all processes
• -a select all with a tty except session leaders
• T select all processes on this terminal
• a select all processes on a terminal, including
  those of other users
• x select processes without controlling ttys
• u display user-oriented format
• ps aux
• ps x
• ps u
• ps a
• kill Terminates a process kill sends the
  specified signal to the specified process. The
  process id can be read by the help of the ps
  command.
• kill 9 125

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BASIC UNIX COMMANDS

• ssh (SSH client) is a program for logging into a
  remote machine and for executing commands on a
  remote machine. It is intended to replace rlogin
  and rsh, and provide secure encrypted
  communications between two untrusted hosts over
  an insecure network.
• ssh burcu_at_maslak.be.itu.edu.tr
• scp secure copy (remote file copy program)
• scp file burcu_at_maslak.be.itu.edu.tr/directory1

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BASIC UNIX COMMANDS

• startx The startx script is a front end to xinit
  that provides a somewhat nicer user interface
  for running a single session of the X Window
  System. It is typically run with no arguments.
• Startx
• logout Exits from the current user.
• Logout
• reboot Stops the system.
• Reboot
• poweroff Stops the system.
• Poweroff

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Text Editing in UNIX Environments

• In many UNIX environments like GNU/Linux, the
  system provides more than one text editor. We
  will discuss vi, joe and pico here.
• VI Vi stands for visual, because it was an early
  text editor that actually showed you the text you
  were creating and what the resulting changes
  looked like. Vi is generally available on every
  UNIX system you might come across for the rest of
  your life.
• w writes the file to disk (if "file" is
  already defined)
• q quit vi
• wq save some typing same as w and then q

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Text Editing in UNIX Environments

• JOE

JOE is a powerful text editor with many
capabilities. Above is a screen shot of the help
screen of JOE.
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Text Editing in UNIX Environments

• Pico

This editor has all the basic functions for
beginners and a quick solution to editing text
files for everyone.