An Introduction to LinuxAn Introduction to Linux

John SwinbankJohn Swinbank

CompsocCompsoc

1313thth November 2001 November 2001

Part OnePart One

Why install Linux, and how Why install Linux, and how to go about doing so.to go about doing so.

What is Linux?What is Linux?

• For the purposes of this talk, a Unix For the purposes of this talk, a Unix like operating systemlike operating system

• It’s not directly descended from Unix, It’s not directly descended from Unix, but it’s designed to work along the but it’s designed to work along the same linessame lines

• At the introductory level of this talk, At the introductory level of this talk, much of what we say about Linux much of what we say about Linux applies to other Unix like systems, for applies to other Unix like systems, for example Free/Net/OpenBSDexample Free/Net/OpenBSD

Why Linux?Why Linux?

• StableStable

• PowerfulPowerful– Wide range of capabilitiesWide range of capabilities– Flexible user interfaceFlexible user interface

• Free (Open Source)Free (Open Source)

• Wide range of toolsWide range of tools– Particularly for Particularly for

development, networking development, networking and so on.and so on.

• A great learning A great learning resourceresource

• Why not?Why not?– It’s not Windows; It’s not Windows;

need to learn need to learn something newsomething new

– Doesn’t run MS Doesn’t run MS OfficeOffice

– Doesn’t run many Doesn’t run many of the latest gamesof the latest games

– The Unix command The Unix command line isn’t for line isn’t for everybodyeverybody

What is Linux What is Linux reallyreally??

• Linux itself is just kernelLinux itself is just kernel– The heart of the system; The heart of the system;

takes care of memory takes care of memory management, interrupt management, interrupt handling…handling…

– First released by Linus First released by Linus Torvalds on 17Torvalds on 17thth September 1991September 1991

– Still maintained by Linus, Still maintained by Linus, with input & patches from with input & patches from interested developers all interested developers all over the world.over the world.

• The kernel is only The kernel is only useful when used in useful when used in conjunction with other conjunction with other softwaresoftware– GNU ProjectGNU Project– XFree86XFree86– OthersOthers

• All this comes nicely All this comes nicely packaged up for you packaged up for you in a distributionin a distribution

What does a distribution do? What does a distribution do?

• Takes the kernel & Takes the kernel & other software and other software and sells/gives them to sells/gives them to youyou

• Provide a “friendly” Provide a “friendly” method of installing method of installing the systemthe system

• Provide security Provide security updates and bug updates and bug fixesfixes

• Provide a method Provide a method for installing and for installing and removing extra removing extra softwaresoftware– A ‘packaging’ A ‘packaging’

systemsystem

• Provide their own Provide their own utility software, e.g.utility software, e.g.– Printer setup,Printer setup,– Network setup,Network setup,– And so onAnd so on

Which distribution to use?Which distribution to use?

• A matter of A matter of personal preferencepersonal preference

• RedHatRedHat– Big, professional, Big, professional,

very widely usedvery widely used

• DebianDebian– Open development Open development

model, excellent model, excellent packaging systempackaging system

– I use DebianI use Debian

• MandrakeMandrake– Aims to be very easy Aims to be very easy

to install and useto install and use

• SuSESuSE– Compromise between Compromise between

RH and Mandrake(?)RH and Mandrake(?)

• SlackwareSlackware– Most traditional; little Most traditional; little

extra help extra help

InstallationInstallation

• Varies from distribution to distributionVaries from distribution to distribution• Most modern distibutions make it easy:Most modern distibutions make it easy:

– Buy CD / download and burn CD imageBuy CD / download and burn CD image– BootBoot– Follow instructionsFollow instructions

• Need to think about partitioning.Need to think about partitioning.• Will install a boot loader (probably LILO or Will install a boot loader (probably LILO or

GRUB, maybe something else). This needs GRUB, maybe something else). This needs to be configured to boot whatever other to be configured to boot whatever other operating systems you have installed.operating systems you have installed.

Useful resources for part Useful resources for part oneone• http://perso.wanadoo.fr/levenez/unix/http://perso.wanadoo.fr/levenez/unix/• http://www.kernel.org/http://www.kernel.org/• http://www.gnu.org/http://www.gnu.org/• http://www.redhat.com/http://www.redhat.com/• http://www.debian.org/http://www.debian.org/• http://www.suse.com/http://www.suse.com/• http://www.linux-mandrake.com/en/http://www.linux-mandrake.com/en/• http://www.slackware.com/http://www.slackware.com/• http://http://www.linuxemporium.co.ukwww.linuxemporium.co.uk//

Part TwoPart Two

Ok, so it’s installed – what Ok, so it’s installed – what next?!next?!

UsersUsers

• Linux is an intrinsically multi-user systemLinux is an intrinsically multi-user system• Every user on the system has their own username Every user on the system has their own username

& password& password• The The rootroot user has ultimate power to run the user has ultimate power to run the

system. You should system. You should not not log in as log in as root root unless you unless you really need toreally need to– Even if you think you need to be root, consider tools Even if you think you need to be root, consider tools

such as such as sudosudo instead instead

• During installation, you should have been During installation, you should have been prompted for a root password and also a prompted for a root password and also a username & password for an ordinary user username & password for an ordinary user account.account.

Virtual consolesVirtual consoles

• Demonstrate multi-user capabilities.Demonstrate multi-user capabilities.• After logging in, hit After logging in, hit Alt+F2Alt+F2. You can now . You can now

log in again – as a different user if you like log in again – as a different user if you like – on this new console.– on this new console.

• After logging in, type After logging in, type ww to see that you to see that you really are logged in twice.really are logged in twice.

• You could also log in from a remote You could also log in from a remote system (using SSH or similar) while still system (using SSH or similar) while still being logged in at the console.being logged in at the console.

ShellsShells

• The shell reads your input at the command line The shell reads your input at the command line and translates it to the operating systemand translates it to the operating system

• Can run external programs (e.g. Can run external programs (e.g. mozillamozilla) or ) or internal shell commands (e.g. internal shell commands (e.g. cdcd))

• String multiple commands together in a shell String multiple commands together in a shell scriptscript

• Various different shells available:Various different shells available:– bash (standard)bash (standard)– tcshtcsh– zshzsh– Others…Others…

Files and directoriesFiles and directories

• Linux shares the concept of files and Linux shares the concept of files and directories with most other everyday systems.directories with most other everyday systems.

• In general, a filename can contain any In general, a filename can contain any character except “/”, and is limited to 256 character except “/”, and is limited to 256 characters long.characters long.

• Directories work in much the same way as in Directories work in much the same way as in DOS based systems, except that instead of “\” DOS based systems, except that instead of “\” we use “/”.we use “/”.

• Note the case sensitivity – Note the case sensitivity – Mozilla Mozilla and and mozillamozilla are are notnot the same! the same!

The directory treeThe directory tree

• Unlike DOS, not directly related Unlike DOS, not directly related to the physical disk/partition to the physical disk/partition layoutlayout

• Some directories are actual Some directories are actual filesystems; others, like filesystems; others, like /proc/proc, , are generated by the kernelare generated by the kernel

• Device files, usually in the Device files, usually in the /dev/dev directory are not standard files, directory are not standard files, but actually an interface to but actually an interface to devices. For example, reading devices. For example, reading /dev/mouse/dev/mouse might show data might show data coming from the mousecoming from the mouse

• A disk partition can be mounted A disk partition can be mounted on any directory in the treeon any directory in the tree

Noteworthy directoriesNoteworthy directories

• /bin/bin– Programs needed to run the Programs needed to run the

systemsystem• /dev/dev

– Device filesDevice files• /etc/etc

– Configuration filesConfiguration files• /home/home

– Users home directoriesUsers home directories• /lib/lib

– Shared libraries needed to Shared libraries needed to run the systemrun the system

• /proc/proc– Provides information about Provides information about

running process and the running process and the state of the kernelstate of the kernel

• /sbin/sbin– Like Like /bin/bin, but commands , but commands

only needed by root useronly needed by root user• /usr/usr

– Programs, libraries, etc not Programs, libraries, etc not essential for system essential for system running.running.

• /var/var– Log files, mail spool and so Log files, mail spool and so

on.on.

NavigatingNavigating

• cdcd– Change directoryChange directory– Equivalents:Equivalents:

• cd /home/jdscd /home/jds• cd ~jdscd ~jds• cd cd (assuming you’re (assuming you’re

logged in as jds)logged in as jds)• lsls

– List directory contentsList directory contents• mkdirmkdir

– Make a new directoryMake a new directory

• cpcp– Copy files/directoriesCopy files/directories

• rmrm– Delete files or Delete files or

directoriesdirectories

• mvmv– Move files or directoriesMove files or directories

• less less (or (or moremore))– View the contents of View the contents of

filesfiles

Help! Too many commands!Help! Too many commands!

• manman is your friend. is your friend.– man cpman cp

• Help on Help on cpcp– man -k cpman -k cp

• List of everything which has “cp” in its description (ok, List of everything which has “cp” in its description (ok, there’s lots of them, bad example ;-) )there’s lots of them, bad example ;-) )

– man manman man• How does man actually work?How does man actually work?

• info info is the preferred GNU system for is the preferred GNU system for documentation.documentation.– A pain in the neck to useA pain in the neck to use– Try the Try the pinfo pinfo viewerviewer

Standard I/O streamsStandard I/O streams

• Many programs take input from standard Many programs take input from standard input and produce output on standard input and produce output on standard ourput.ourput.

• Error messages are sent to standard error.Error messages are sent to standard error.

• Often, stdin is the keyboard and stdout & Often, stdin is the keyboard and stdout & stderr are the screenstderr are the screen– But they can be redirected.But they can be redirected.

• Example: Example: catcat..– Reads data from stdin. Sends it to stdout.Reads data from stdin. Sends it to stdout.

PlumbingPlumbing

• We can redirect standard output to a fileWe can redirect standard output to a file– cat > filenamecat > filename

• Or bring standard output in from a fileOr bring standard output in from a file– cat < filenamecat < filename

• Or bothOr both– cat < file1 > file2cat < file1 > file2

• We can also send the standard output of one We can also send the standard output of one command to the standard output of otherscommand to the standard output of others– cat < file1 | cat > file2cat < file1 | cat > file2

• The “Unix philosophy”: don’t have one The “Unix philosophy”: don’t have one monolithic, do everything application. Have small monolithic, do everything application. Have small programs that do one thing well & can work programs that do one thing well & can work together.together.

Groups & permissionsGroups & permissions

• Each user can be a Each user can be a member of one or member of one or more groupsmore groups– groupsgroups command command

• Each file/directory is Each file/directory is owned by a user and a owned by a user and a groupgroup– ls –lls –l

• The file owner can set The file owner can set permission on who permission on who can can read/write/execute a read/write/execute a file.file.

• Permissions can be set Permissions can be set for each of owner, for each of owner, group and others.group and others.– chmod chmod commandcommand

• Permissions are listed Permissions are listed in the form in the form rwxrwxrwxrwxrwxrwx in the output of in the output of ls –lls –l– Three groups of threeThree groups of three– Read, write, execute for Read, write, execute for

each ofeach of– User, group, othersUser, group, others– The first character The first character

represents the type of represents the type of filefile

LinksLinks

• Give a single file more than one nameGive a single file more than one name• Create links using Create links using lnln• Hard linksHard links

– Multiple file names pointing to the same inodeMultiple file names pointing to the same inode– ls –Ils –I– ls –l ls –l displays number of links to filedisplays number of links to file– A directory is a file containing information about link to A directory is a file containing information about link to

inode associationsinode associations• Every directory contains at least two links: “.”, pointing to Every directory contains at least two links: “.”, pointing to

itself, and “..” pointing to its parentitself, and “..” pointing to its parent

• Symbolic links (symlinks)Symbolic links (symlinks)– Not linked by having the same inodeNot linked by having the same inode– ls –lls –l displays link target – note the filetype! displays link target – note the filetype!

Processes Processes

• Linux is a multitasking system – there can be Linux is a multitasking system – there can be many processes running at the same timemany processes running at the same time– psps

• Each process has a unique process ID (‘pid’) Each process has a unique process ID (‘pid’) numbernumber

• Processes can run in the foreground or in the Processes can run in the foreground or in the backgroundbackground– There can only be one foreground process at any given There can only be one foreground process at any given

time. It is this processes with which the user interacts.time. It is this processes with which the user interacts.• Suspended processes are temporarily stopped, Suspended processes are temporarily stopped,

and can be sent either to the foreground or and can be sent either to the foreground or background as required. background as required.

• The shell can control processesThe shell can control processes

Job ControlJob Control

• Kill the foreground process: Kill the foreground process: Ctrl+CCtrl+C• Suspend the foreground process: Suspend the foreground process: Ctrl+ZCtrl+Z• Send the suspended process to the:Send the suspended process to the:

– Foreground: Foreground: fgfg– Background: Background: bgbg

• Start a process in the background: append an Start a process in the background: append an && to to the commandthe command– E.g.E.g. yes & yes &– Note the PID and job numberNote the PID and job number

• Check the status of processesCheck the status of processes– jobsjobs

Killing processesKilling processes

• Use the Use the kill kill commandcommand– Either with the PID, for example:Either with the PID, for example:

• kill 22916kill 22916

– Or with the job number:Or with the job number:• Kill %2Kill %2

– Note the ‘%’!Note the ‘%’!

• Or use Or use killall killall with the command name:with the command name:– yes > /dev/null & killall yesyes > /dev/null & killall yes– Be warned that Be warned that killall killall may may not have the not have the

desired effect on non-Linux systemsdesired effect on non-Linux systems

Useful resources for part 2Useful resources for part 2

• http://www.linuxdoc.org/http://www.linuxdoc.org/

• Your own distribution’s Your own distribution’s documentationdocumentation

•man hierman hier•man bashman bash

• Other man pages (ps, ls, ln, kill, Other man pages (ps, ls, ln, kill, killall…)killall…)

Part ThreePart Three

Essential toolsEssential tools

Text EditorText Editor

• Everybody needs a text editorEverybody needs a text editor• Pick one and learn how to use it well – it’ll Pick one and learn how to use it well – it’ll

save you a lot of time in the long runsave you a lot of time in the long run• Traditional choices are Emacs and Vi (or Traditional choices are Emacs and Vi (or

Vim – Vi Improved)Vim – Vi Improved)• Also worth considering simpler editors for Also worth considering simpler editors for

getting startedgetting started– JoeJoe– PicoPico

• Lots of other editors out there if these Lots of other editors out there if these don’t suitdon’t suit

MailMail

• The “Unix philosophy” The “Unix philosophy” again – several small tools again – several small tools working together. Contrast working together. Contrast with, e.g. Outlook which with, e.g. Outlook which tries to do everything.tries to do everything.

• Mail User Agent (MUA)Mail User Agent (MUA)– Reads & writes mail. Reads & writes mail.

Handles display, Handles display, threading, etcthreading, etc

• Mail Transport Agent (MTA)Mail Transport Agent (MTA)– Sends and receives Sends and receives

messages using SMTPmessages using SMTP

• Mail Delivery Agent (MDA) Mail Delivery Agent (MDA) (optional)(optional)– Delivers messages to local Delivers messages to local

usersusers– User configurable filtering, User configurable filtering,

bounces, etcbounces, etc

• May also need a program May also need a program to retrieve messages from to retrieve messages from a POP3/IMAP server and a POP3/IMAP server and deliver them to the MTA deliver them to the MTA using SMTPusing SMTP

• Of course, there are also Of course, there are also monolithic, Outlook style monolithic, Outlook style applications out thereapplications out there

Package ManagementPackage Management

• Varies from distribution to distributionVaries from distribution to distribution• Most common system is RPM, developed & used by Most common system is RPM, developed & used by

RedHat.RedHat.– Also used by Mandrake, SuSE etcAlso used by Mandrake, SuSE etc

• Also .deb packages, as used by Debian and Also .deb packages, as used by Debian and derivativesderivatives

• Provides for installing new packages, satisfying Provides for installing new packages, satisfying dependencies, full system upgrades etc.dependencies, full system upgrades etc.– The apt-get system used by Debian for this is very The apt-get system used by Debian for this is very

powerful.powerful.– Similar, but perhaps less widely used, systems in the RPM Similar, but perhaps less widely used, systems in the RPM

using worldusing world• It’s worth learning how to use your distributions It’s worth learning how to use your distributions

package management tools properlypackage management tools properly

CompilerCompiler

• Assuming you don’t want to use binary Assuming you don’t want to use binary packages all the time, you’ll need a packages all the time, you’ll need a compilercompiler– You’ll want to compile new kernels yourself, if You’ll want to compile new kernels yourself, if

nothing elsenothing else

• Any sane distribution should ship with gcc, Any sane distribution should ship with gcc, the GNU Compiler Collection (formerly the GNU Compiler Collection (formerly GNU C Compiler)GNU C Compiler)

• Run Run gccgcc. .

Useful resources for part 3Useful resources for part 3

• http://www.vim.org/http://www.vim.org/• http://www.gnu.org/software/emacs/emacs.htmlhttp://www.gnu.org/software/emacs/emacs.html• http://www.xemacs.org/http://www.xemacs.org/• http://www.linuxdoc.org/HOWTO/Mail-User-http://www.linuxdoc.org/HOWTO/Mail-User-

HOWTO/index.htmlHOWTO/index.html• http://www.linuxdoc.org/HOWTO/Mail-http://www.linuxdoc.org/HOWTO/Mail-

Administrator-HOWTO.htmlAdministrator-HOWTO.html• http://www.rpm.org/http://www.rpm.org/• http://www.kitenet.net/~joey/pkg-comp/http://www.kitenet.net/~joey/pkg-comp/• http://www.gnu.org/software/gcc/gcc.htmlhttp://www.gnu.org/software/gcc/gcc.html

Part FourPart Four

The X Window System, or how The X Window System, or how to make a 50-MIPS to make a 50-MIPS

workstation run like a workstation run like a 4.77MHz IBM PC 4.77MHz IBM PC

X: A graphical interface for X: A graphical interface for UnixUnix• If the designers of X-If the designers of X-

Windows built cars, Windows built cars, there would be no there would be no fewer than five fewer than five steering wheels steering wheels hidden about the hidden about the cockpit, none of which cockpit, none of which followed the same followed the same principles – but you'd principles – but you'd be able to shift gears be able to shift gears with your car stereo. with your car stereo. Useful feature, that. Useful feature, that. – Marus J. Ranum, Digital Marus J. Ranum, Digital

Equipment Corporation Equipment Corporation

• Despite the above quote, X isn’t Despite the above quote, X isn’t all bad. It’s actually a all bad. It’s actually a remarkably powerful, network remarkably powerful, network aware windowing system which aware windowing system which has shown a great deal of has shown a great deal of adaptabilityadaptability

• Most Linux distributions come Most Linux distributions come with XFree86with XFree86– An open source implementation An open source implementation

of the X Window Specification of the X Window Specification • X is a huge subject; we’re not X is a huge subject; we’re not

going to attempt to cover it all going to attempt to cover it all here. Instead, I’ll aim to give a here. Instead, I’ll aim to give a flavour of the things X can do flavour of the things X can do and the graphical environments and the graphical environments which make use of it.which make use of it.

Clients and serversClients and servers

• X is network awareX is network aware– Run a program on one machine, have it display on Run a program on one machine, have it display on

anotheranother• The terminology around this is, perhaps, The terminology around this is, perhaps,

counterintuitive…counterintuitive…• An X An X server server runs on the machine where the runs on the machine where the

display is to appeardisplay is to appear• The X The X client client runs on a remote machine and runs on a remote machine and

sends data to the server to displaysends data to the server to display• So, contrary to the usual definitions, you sit at the So, contrary to the usual definitions, you sit at the

server and the clients run remotely!server and the clients run remotely!• (Most of the time on your Linux workstation, the (Most of the time on your Linux workstation, the

clients and the server run on the same machine.)clients and the server run on the same machine.)

X and the GUIX and the GUI

• X itself provides the back end X itself provides the back end needed for a GUI. It doesn’t, needed for a GUI. It doesn’t, however, provide an interface however, provide an interface itself.itself.

• Window management Window management functions – e.g. moving or functions – e.g. moving or resizing windows – are resizing windows – are performed by a window performed by a window manager, which is itself an X manager, which is itself an X client. These range from the client. These range from the spartan (twm) to the complex spartan (twm) to the complex and graphically intensive and graphically intensive (Enlightenment).(Enlightenment).

• There are various different There are various different toolkits for creating graphical toolkits for creating graphical applications, providing applications, providing libraries of widgets such as libraries of widgets such as buttons etc. These range from buttons etc. These range from the old and ugly (Motif) to the the old and ugly (Motif) to the new and shiny (GTK+, Qt)new and shiny (GTK+, Qt)

• No two users can be assumed No two users can be assumed to have the same window to have the same window manager and different manager and different applications can use different applications can use different toolkits (or even write their toolkits (or even write their own). Therefore, there’s a own). Therefore, there’s a lack of consistency about the lack of consistency about the average X desktop – this average X desktop – this makes things ugly and can be makes things ugly and can be hard to use.hard to use.

Desktop environmentsDesktop environments

• Attempt to produce a consistent Attempt to produce a consistent environment and set of applicationsenvironment and set of applications

• Two major projects along the same linesTwo major projects along the same lines– GNOME, using the GTK+ toolkitGNOME, using the GTK+ toolkit– KDE, using the Qt toolkitKDE, using the Qt toolkit– (also XFce, which aims to be more lightweight)(also XFce, which aims to be more lightweight)

• Some people (including me) find that the Some people (including me) find that the desktop environments are big, slow and desktop environments are big, slow and ugly without actually adding much usabilityugly without actually adding much usability– Luckily, it’s possible to use most KDE/GNOME Luckily, it’s possible to use most KDE/GNOME

software without running the whole environmentsoftware without running the whole environment

Useful resources for part Useful resources for part fourfour

• http://www.xfree86.org/http://www.xfree86.org/

• http://www.xwinman.org/http://www.xwinman.org/

• http://www.gtk.org/http://www.gtk.org/

• http://www.trolltech.com/products/qt/http://www.trolltech.com/products/qt/

• http://www.kde.org/http://www.kde.org/

• http://www.gnome.org/http://www.gnome.org/

• http://www.xfce.org/http://www.xfce.org/

The EndThe End

Comments, questions, pub…Comments, questions, pub…