ITR3 lecture 6: intoduction to UNIX

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ITR3 lecture 6 intoduction to UNIX

• Thomas Krichel
• 2002-10-21

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Today we have fun with

• Disks
• Unix basics
• Important unix utilities

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Files, directories and links

• Files are continuous chunks data on disks that
  are required for software applications.
• Directories are files that contain other files.
  Microsoft calls them folders.
• A link is a file that contain the address of
  another file. Microsoft call it a shortcut.

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Structure of a disk

• Disks are round devices divided into tracks and
  sectors.
• A hard disk may have several physical disks.
• Sector is 571 bytes long
• 512 bytes are used by the user
• The rest is reserved for disk operation
• The disk spins, a head reads and writes data.

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Data integrity

• The special data in each sector is kept there to
  try ensure that the user data is safe.
• It contains a summary of the user data.
• When the summary and the user data no longer
  match, the summary can be used to correct the
  user data.
• SMART disks are those that can monitor if they
  are a in good shape.

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Formatting a floppy

• Physical formatting
• writing tracks
• writing sectors
• Logical formatting
• labeling each sector
• create boot record
• create file allocation table (FAT)

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Formatting a hard disk

• That is the same as formatting a floppy but
• Between physical and logical formatting, the hard
  disk may be partitioned.
• This allows for several logical disks on the same
  physical disk
• Therefore the boot record is more complicated
  than on the floppy and called a master boot
  record MBR.
• Example dual boot Linux/Windows machine

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Unix file conventions

• In UNIX the root directory is /.
• / is the directory separator.
• A number of special files in /dev represent
  devices.
• Each device is mounted as a subdirectory of the
  root directory. Example
• mount /dev/fd0 /floppy
• You need to be root to do this.

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Device names

• /dev/fd0 first floppy drive
• /dev/fd1 second floppy
• /dev/sda first SCSI disk
• /dev/sdb second SCSI disk
• /dev/scd0 first SCSI CD-ROM
• /dev/hda master disk on IDE primary controller
• /dev/hdb slave disk on IDE primary controller
• /dev/hdc master disk on IDE secondary controller
  
• /dev/hdd slave disk on IDE secondary controller

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Root user

• root is the user name of the superuser.
• The superuser has all priviledges.
• Most of the time, you should not work as the
  superuser, but use your own private account.

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Permission model

• Permission of files are give to the owner, the
  group, and the rest of the world.
• A group is a grouping of users. Unix allows to
  define any number of groups and make users a
  member of it.
• The rest of the world are all other users who
  have access to the system.

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Listing files

• ls lists files
• ls l make a long listing. It contains
• Date
• Owner
• Group
• Size
• permission

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First element in ls -l

• Type indicator
• d means directory
• l means link
• - means ordinary file
• 3 letters for permission of owner
• 3 letters for permission of group
• 3 letters for permission of rest of the world
• r means read, w means write, x means execute

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Change permission chmod

• A permission is a number
• 4 is read
• 2 is write
• 1 is excute
• Permissons are three numbers, for owner, group
  and rest of the world.
• Example chmod 764 file
• Directories need to be executable to get in them

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Change owner and group

• chown user file
• chgrp group file
• Usually you need to be root to do this.
• Add users with adduser, follow instructions.
• userdel rids you of an annoying user.

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shell

• The shell is a command line interpreter.
• When you login, a shell is started for you.
• Shells include
• Bourne shell sh -- Korn shell ksh
• C shell csh -- extended C shell tcsh
• Bourne again shell bash z shell zsh
• The default shell will be bash, which is linked
  to the default place where the shell is found,
  /bin/sh

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General structure of commands

• commandname flag --option
• Where commandname is a name of a command
• Flag can be a letter
• Several letters set several flags or form an
  option
• An option can also be expressed with - - and a
  word.

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Bash features

• cd is a command to change directory
• File names and command names can be completed
  with TAB
• The command history can be activated with the
  arrow keys of the keyboard
• Environment variables can be completed
• So login now

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Environment variables

• Are variable that the shell knows about.
• Env lists all of them
• PATH, where the executable files are searched
• EDITOR, the default editor
• PS1, the primary prompt
• HOME, the home directory

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Setting and showing them

• LWORDlibrary
• Set lword to be library
• export LWORD
• Make it visible to the shell
• echo LWORD
• Show the value.
• Other example
• PATHPATHHOME/bin

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Copying and removing

• cp file copyfile
• scp user_at_machinefile user_at_machinefile
• User is a user
• Machine is a machine
• File is the path to a file
• Of course you will need permissions here!
• rm file there is no recycling bin!!
• -r flag copies and deletes recursively

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Directories and files

• mkdir file makes a directory
• rmdir file removes it
• touch file
• makes a new empty file
• sets the time on an existing file
• more file
• Pages contents of file, no way back
• less file
• Pages contents of file, u to go back, q to
  quit

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Important programs

• echo, shows argument on the screen
• cat file, shows file on the screen
• who, shows who is logged in
• top, shows processes
• ln s file1 file2 create a link form file2 to
  file1. pretty confusing
• man command shows manual for command
• man k term looks for commands with the keyword
  term

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grep

• Looks up an expression in a file
• Syntax is one of simple regular expressions
• READ the man page for this command. This is an
  important reading and will be part of the quiz
  after the installation

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kill

• Sends signal to a process.
• You need to know the number of the process, you
  can do that with ps
• Signal 9 will kill the process
• Signal HUP will hang up the process, it will read
  its configuration file again .

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find

• Finds files
• Has a exec flag that allows you to execute
  programs on the files found.
• READ the man page for this command. This is an
  important reading and will be part of the quiz
  after the installation

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http//openlib.org/home/krichel

• Thank you for your attention!