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ITR3 lecture 6: intoduction to UNIX Thomas Krichel 2002-10-21.

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Presentation on theme: "ITR3 lecture 6: intoduction to UNIX Thomas Krichel 2002-10-21."— Presentation transcript:

1 ITR3 lecture 6: intoduction to UNIX Thomas Krichel 2002-10-21

2 Today we have fun with Disks Unix basics Important unix utilities

3 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.

4 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.

5 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.

6 Formatting a floppy Physical formatting: –writing tracks –writing sectors Logical formatting: –labeling each sector –create boot record –create file allocation table (FAT)

7 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

8 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.

9 Device names /dev/fd0 first floppy drive /dev/fd1 second floppy /dev/sdafirst SCSI disk /dev/sdbsecond SCSI disk /dev/scd0 first SCSI CD-ROM /dev/hdamaster 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

10 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.

11 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.

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

13 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

14 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…

15 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.

16 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

17 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.

18 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

19 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

20 Setting and showing them LWORD=library –Set lword to be library export LWORD –Make it visible to the shell echo $LWORD –Show the value. Other example PATH=$PATH:$HOME/bin

21 Copying and removing cp file copyfile scp user@machine:file user@machine:file –User is a user –Machine is a machine –File is the path to a file –Of course you will need permissions here! rm filethere is no recycling bin!! -r flag copies and deletes recursively

22 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

23 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

24 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

25 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.

26 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

27 http://openlib.org/home/krichel Thank you for your attention!


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