ITR3 lecture 6: intoduction to UNIX

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/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

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 userfile • 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 file there 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!