Unix/Linux basics

1. Unix/Linux basics Operating systems lab Gergely Windisch

2. Unix • It was created around the 70’s for mini computers. It has spread to the mainframes, workstations and then to personal computers • Simplicity was always an aim • The kernel was written in C (almost from the beginning) -> new • The many flavors of Unix and the incompatiblity that came with it is still around • Multiple unix versions: good, because competition enhancesthere is no one accepted solution (incompatiblity) • Standardization work, multiple standards (the important is „what”, not „how”) • Commercially avalable Unix versions: Sun/Solaris, HP/HP-UX, IBM/AIX • Interesting: Mac OS X (BSD based) Multiuser, multitask operting system

3. A Linux • Born in 1991– Linus Torvalds – x86 • Started life as a terminal app for minix • Nowdays an alternative to Unix and Windows systems • Linux is not Unix, but similar • Unix like in appearance and programming API, different under the hood • The kernel is not held by one company but is developed by the community (with centralized management - Linus) • The code base is developed by the community • Wide spectrum of supported hardware architectures • There are some pioneer solutions, but there are also some weak spots compared to the „big” Unix versions (thread management in the 2.4 kernels for example)

4. Linux - distributions • Linux distributions • „A Linux distribution (also called GNU/Linux by some vendors and users) is a member of the family of Unix-like software distributions built on top of the Linux kernel. Such distributions (often called distros for short) consist of a large collection of software applications such as word processors, spreadsheets, media players and database applications. The operating system will consist of the Linux kernel and, usually, a set of libraries and utilities from the GNU project, with graphics support from the X Window System. „ - Wikipedia • http://upload.wikimedia.org/wikipedia/commons/8/8c/Gldt.svg

5. Linux – distros (cont’d) • Even more colorful than unix • free and commercial as well • Most important commercial versions: RedHat and Suse • Free versions: Debian and co. (debian based), Fedora (RedHat based) and openSuse • Live CD try without installation • Knoppix: http://www.knoppix.org/ (Debian GNU/Linux) • Demolinux: http://www.demolinux.org/ (Mandrake) • More at: http://en.wikipedia.org/wiki/Live_CD

6. Useful links • http://www.hup.hu – Hungarian Unix Portal • Only in hungarian  for those of you who are interesten in the language • http://www.kernel.org – Place of the linux kernel • http://www.distrowatch.com – home of practically all the distributions

7. Where can I practice? • Downloading linux: • www.ubuntu.com, www.debian.org, www.slackware.com, www.suse.de, en.opensuse.org, www.distrowatch.com • VMWARE pre-built images:http://www.vmware.com/vmtn/appliances/directory/cat/45

8. Where can I get help? • Everywhere! • The Hungarian Unix Portal:http://hup.hu (again, for the eager minded) • Linux Knowledge Base and Tutorial: http://www.linux-tutorial.info • http://en.wikipedia.org/wiki/Linux • Linux Shell Scripting Tutorial:http://www.freeos.com/guides/lsst/ • http://www.google.com

9. The graphical world… • Distributions • RedHat (www.redhat.com) • Ubuntu (www.ubuntu.com) • Debian (www.debian.org) • Slackware (www.slackware.com) • Mandriva (www.mandriva.com) • Suse (opensuse.org) • Let’s look at some of them

10. Linux basics • Linux is like Unix – API and the command line is unix compatible • As far as we get into the subject, all the distros are the same • Makes no difference which one we install

11. Linux basics (cont’d) • Multiuser: we do not rule the whole machine – just one session (many concurrent users) • Authentication before being able to do anything – user + password • System access is restricted – we can only modify those to which we have the permissions • Simple users cannot change (break) the system (for that would affect others)!

12. Because of the multiuser environment, linux is somewhat different to other pc operating systems: one machine, multiple terminals. Still apparent today: virtual console • Text based mode (shell) and graphical interface (X) • GUI is spreading like mushroom after the rainy season - but the main interface for setting the system up is still the console. • Terminal access via TCP/IP, earlier it was via RS-232 (serial port) • In a PC based desktop solution the machine and the view isn’t separated, however it is still separated underneath (modularity)

13. Root user • Every OS needs a superuser who can access everything, set things up • In Unix, the role is called root. Root has total control over the machine • There can only be one root, it’s task cannot be given to multiple users • Possible solutions: • sudo, RBAC (hasn’t really caught on) • Security Enhanced Linux

14. Let’s start linux! • VMWare workstation • Ubuntu8.10, XUbuntu8.10, Ubuntu 8.10 Server • Credentials: • hallgato / nik119 • Take a good look around the system • Try programs like gimp, openoffice, kate, xcalc, gmplayer, firefox etc. • Install software using Synaptic • Packages vs. source

15. Command line • Login can be Local (console or terminal) Remote: telnet, ssh, putty (Windows ssh client) On-Line help: man – reference, not a tutorialpractice, practice, practice • user: • hallgato:nik119 • Commands: • who am i • uname -a • ls • ls / • man ls

16. Take a look around! • Ubuntu 8.10 tty1 • Last login: When did we log in last • 2.6.27-2-386: current kernel • there can be multiple kernels on the machine • Ubuntu Server does not have X

17. Kernel • Three number versioning scheme • Kernel version • Major revision • Minor revision • Fourth number for immediate patches (2.6.8.1) • 1991 – Linux 0.01 • 1994 – Linux 1.0 • 1996 – Linux 2.0 • 1999 - Linux 2.2.0 • 2001 - Linux 2.4.0 • 2003 - Linux 2.6.0

18. Console • The character interface is called console (or terminal) • Virtual consoles. Switch: alt+F1 – alt+F6 • Command line interpreter is BASH (shell) • Use tab key to complete commands • mor[tab]: more • cd /sbi[tab]: cd /sbin • press tab twice if nothing happens

19. Parancsok • man : Manual – reference • There is a manual for almost every command • man ls • ls –help • man man • Commands • command • switch: - • full name of switch: -- • eg: ls -a == ls --all

20. Where are we? Who are we? • uname -a • who • who am i (whoami) • w • last • ls • ls /

21. Directories • Important directories • / : root directory • /etc: home of the configuration files • /bin: executable commands • /var: files that change a lot : log, spool, mail • /home: users own directories • /usr/local: files of installed applications

22. Könyvtárak • /sbin: executables reserved for root • /boot: stuff for booting • /root: own directory of the root • /proc: system data (dynamic) • cat /proc/cpuinfo (later)

23. Partitioning • / : root • /home • Swap • /boot • /usr • /var

24. File basics • All files are byte streams • Files are denoted by their names • Filename can be quite long • There is no extension – can contain . • Hierarchical structure • Directory separator: / (and not \ !!!)

25. File alapok (2) • echo „Hello” > apple.txt • ls • ls -l • cat apple.txt • echo „Leo” >> apple.txt • cat apple.txt • echo „Hello World” > apple.txt • cat apple.txt

26. touch orange.txt • ls • ls -l • Joker characters: • *: Denotes any number of chars • ?: Denotes just one char

27. Tricky filenames (1) • echo „Hallo” > ‘apple*’ • echo „Welt” > appletree • echo „Hi”> applewine • cat appletree • cat applewine • cat apple*Escape character: '\' --> cat apple\*

28. Tricky filenames (2) • echo „apple” > aa • echo „orange” > bb • echo „fruit” > 'aa bb' • ls • cat aa bb • cat 'aa bb'

29. Print contents of file (1) • cat applewine • cat /bin/catWhat happened to the console?

30. Print contents of file (2) • cat applewine • cat /bin/catWhat happened to the console?cat should only be used for printing text files • /usr/bin/cat is a binary, with control codes • Print contents of any file: od • od /bin/cat • od -c /bin/cat

31. File type • Extension does not always help • file command • file /usr/bin/file • Uses file headers • Try tricking it into making a mistake: • cp /usr/bin/apt-get . (use tab!) • file apt-get • mv apt-get something.mp3 • file something.mp3

32. File commands • Remove: rm • rm apt-get • rm –r: remove recursively (subdirectories as well) • Copy: cp • cp apple.txt orange.txt • ls • Move: mv • mv apple.txt orange.txt • ls

33. Directories • cwd: current working directory • pwd command returns cwd • ~: own directory of user • echo ~ • /home/user (/root): default dir to the user • . : current directory • .. : parent directory

34. Directories • Relative path<--> absolute path • ls /etc • pwd • ls ../../etc • ls .. • ls . • PATH • echo $PATH • ./program

35. Directories • Moving around • cd • cd /etc • cd etc • cd jumps to the user home directory • cd ~ jumps to the user home directory • cd .. jumps to the parent directory • cd / jumps to the root directory

36. Directories • Create directory: mkdir • mkdir fruit • touch fruit/apple • touch fruit/orange • ls -l orange • ls –R, ls * : list subdirectories • delete directories: rmdir

37. Hidden files • Everything that starts with '.' is hidden • touch orange • touch .orange • ls • ls –a • orange and .orange are completely different

38. Multiple commands • &&: command1 && command2 • Run command 2 after command 1 • ls –l / && echo „success” • ls –l /homme && echo „success” • ||: command1 || command2 • run command2 after command 1 if command 1 failed • ls –l / || echo „failure” • ls –l /homme || echo „failure”

39. Pipe, background • |: pipe • ls –l /etc | more • &: start command in background (later)‏ • command &

40. Practice (for it makes perfect) Create the following directory structure: ~ directory1 directory2 directory3 directory4 directory41 directory11 directory12 directory21 directory22 directory111 directory23 directory112 Bonus: create a shell script which creates directories like so (creatdir directory113 – directory 11 and 1 are created) directory113

41. Practice Create files in each directory where the name of the file is file<number>. The <number> should be the number of the directory (eg: directory131: file131) Use touch, >, >> to create files Use TAB Use relative and full path Use your imagination For bonus points: create a shell script that when gets a filename like this, will create the directory and put the file in it