Introduction to Unix and Networks

Title: Introduction to Unix and Networks 

Prerequisites: None 

Languages: None 

Time: 1hour 

Schedule: Chapter 2 

Requirements: Linux on a networ k 

$man unix 

core dump 

$ 

Summar y: 

This is a shortintroduction to computing facilities based on Linux PCs with networ king connection. 

Learning Objectives: 

To practise the connect / login and logout procedures & remote access to the networ k 

To gain some familiar ity and confidence with simple Unix commands and the use of X-windows 

To contrast the File Manager and command line approach to file handling. 

Understand the interrelationship between the var ious systems. 

To understand how totransfer files around the networ k and access printers. 

To use an editor such as vi or emacs. 

Be confident in using basic Internet facilities. 

To dev elop simple C programs. 

Commercial Relevance: 

Until recently,any major database server orlarge host connected to the Internet would have run Unix, 

probably Sun/Solaris or HP/UX. Microsoft Windows has now begun to capture some of this sector. Another 

recent change is the emergence of Linux as a force within the commercial marketplace, especially for "backroom" 

systems. 

3p11 

3p28 

3p27 

Jaz 

164.11.222.x 

164.11.7.x 

Hub1 

Hub2 

164.11.8.x 

Ether 

Switch 

Ether 

switch 

por tal.netlab 

CEMS networ k 

old 

Kenny 

Kyle 

Kenny 

Schematic layout of CEMS Netlab networ k 

1 

164.11.222.200 

164.11.222.164 

164.11.222.253 

Sun 

164.11.11.13 

Ser ver - milly 

NAS 

164.11.8.48 

Networ k Attached 

Storage 20 TB

The role of an operating system, such as Unix or Windows-XP, istoassist the user and protect the hardware. 

Operating systems are large, complex programs, orgroups of programs, designed to help application 

programs employ the resources of the computer more securely and efficiently. With multi-user systems, and 

ev en single-user multi-tasking systems, the allocation, arbitration and control of shared resources is a 

pr imary function. When the computer is shared between a number of users, the problem of data security 

becomes paramount. More and more, the operating system provides convenient access to a networ k and the 

Inter net beyond. Unix remains an important commercial example, and has also attracted more enthusiasts 

with the introduction of the freely distributed Linux version. 

1. Logging on 

This wor ksheet requires you to wor k with Linux, so you may have toreboot the PC. Check tosee if your PC 

needs to be turned on, or just rebooted if it is currently running Windows. Log on with your CEMS user id 

and netlab password which may bedifferent from that for the main networ k. Note that Unix respects the 

upper/lowercase distinction, so be careful entering the allocated password. The password scheme for Netlab 

Linux is separate from the main Unix and PC networ ks in the rest of the University. Yes, you could end up 

having to remember 4 distinct passwords! At the last count, I discovered that I was remembering 13 different 

passwords and identity codes. How ever, at UWE, you can set them all the same value if you wish. 

Although it would be nice to have a single password for all UWE facilities: librar y, email, ITS computing, 

CEMS computing, WiFi connection, remote login from home, web page administration, this has not yet been 

achieved and you will still need to remember several distinct passwords. You can set most of these to the 

same value if that suits you. But do not overlook the need for effective, appropr iate secur ity. Because the 

university takes a ver y ser ious view onplager ism (copying). Allowing others to get access to your personal 

files can lead you into deep trouble with UWE. Certainly NEVER allow others the right to send emails from 

your account when you are not present. 

Changing a Unix password to some more personally memorable item is easy, but make sure you do 

remember your new password. For security reasons it is good practice to include a non-letter (number or 

punctuation) in the password to discourage "dictionary scanning". Car numbers are a good source, but don’t 

be daft and use your current number plate. 

Tr y guessing a friend’s password, and note down your strategies. Most malign hacking involves reading a 

password from a PostIT note stuck toanadmin terminal, or given over the phone. 

Av oid guessable items for your own password! 

We usually recommend that you do not change the original, unmemorable passwords immediately. Wait until 

you are more familiar with the UWE system. But this is the way you do it: 

rob@kenny> passwd 

Please enter your old password: 

Please enter your new password: 

Please enter your password again: 

Your password has now been changed. 

rob@kenny> 

When you login (or start anew shell), the Unix operating system will try toexecute setup instructions held in 

anumber of standard script files. Typically these instructions will initialize some environment var iables, such 

as PS1, PATHand TERM. Look into the following files, note they are hidden fromls by the leading ".". You 

must usels -al or select [View] -> [Show Hidden Files] for the file browser. 

1 /etc/profile at login, by the initial shell 

2 ~/.bash_profile 

3 ~/bash_login 

4 ~/.profile 

~/.bashrc at each new shell start up 

~/bash_logout by initial shell at logout 

There are 3 files you really need to understand when customizing the bash shell: /etc/profile, ~/.bash_profile, 

and ~/.bashrc. Inspect /etc/profile (more /etc/profile which holds global initialization commands for 

ev ery user. Each user can have an personalised ~/.bash_profile which is executed only at login. It is NOT 

executed for each shell, only the login shell. However, ~/.bashrc is executed for each new shell except the 

2

login shell. It is recommened that you put all your special shell customizations into your .bashrc file, and set 

.bash_profile to call .bashrc with the command:source ~/.bashrc. 

The most important set-up action is to initialise thePATH variable. This tells the Unix shell where to find 

executable programs. Ifitisnot set up, noprograms can be found, or run. Quite tragic. Now look at its value 

for your session: 

# printenv PATH 

/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games:$HOME/bin 

# 

To add another directory, such as your current one (indicated by the .), to the PATH, 

you could use the following: 

# export PATH=${PATH}:. 

look here 

# printenv PATH 

/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games:$HOME/bin:. 

# 

Note the use of { } to define clearly what the var iable name is. Otherwise the $ prefix could extend in scope to 

the end of the line. Alter natively, you could addexport PATH=${PATH}:. to your.bash initialization file. 

As an exper iment, tr y clear ing PATH, and see what results. But before you do it, make sure you know how to 

reset it: 

COMMENTS 

# OLDPATH=$PATH save value in PATH 

# PATH="" clear PATH 

# emacs tr y to run an application 

-bash: emacs: No such file or directory error from Linux !! 

# PATH=$OLDPATH restore PATH’s value 

# emacs & all OK now again 

# 

When you are registered on a Unix system as a user, you are allocated a UID (user identity number). Also 

you can join groups of other users. Use the commandswhoami andid to find out who you are. Once logged 

in, you maybeable toswitch user identity usingsu, but at UWE this is a privileged command, limited to 

administrators only. 

2. The Unix Filesystem 

There is a general pattern which all Unix file system hierarchies keep to, although it does var y abit when 

moving between HP/UX, Solaris, and all the Linuxes. When logged in, list the root directory ofyour desktop 

machine: 

# ls -al / 

bin/ etc/ initrd/ local/ proc/ sys/ tmp/ vmlinuz@ 

boot/ floppy/ initrd.img@ mnt/ root/ tftpboot/ usr/ 

dev/ home/ lib/ opt/ sbin/ tftpboot.tgz var/ 

# 

The directory patter n is best expressed in a tree diagram, each of the nodes also elaborate the hierarchy 

fur ther,until the files themselves are reached. Here is the top level director y tree: 

bin boot dev etc home local mnt proc sbin tmp usr var 

Take a look in each of the top level subdirector ies and decide what kind of files, used for what purpose, are 

stored there:cd /bin; ls -al 

3 

/

3. The network 

The UWE CEMS faculty has a main networ k, and an exper imental networ k called Netlab. The main networ k 

has some 17 subnets and 500 hosts (notably milly the main Sun multiprocessor), including all the staff 

rooms,student PC and Unix labs, and so becomes ver y complex. The much smaller exper imental networ k 

only covers 3p11, 3p27, 2p28, 2n24 and the local servers, notably kenny, asinthe preceding diagram. 

This networ k diagram only shows the interconnectivity of the var ious hosts accessible from the Netlab 

networ k. The main University networ k is really too complex tobother with, but from the users’ point of viewit 

all acts like agigantic central switch, routing packets between all the subnets. 

The distribution and routing of data packets along local area networ ks (LAN) and out across the Internet is 

based on the TCP/IP protocols. These protocols specify data packet for mats, command codes, responses 

and conventions. They were originally devised as part ofthe US Department of Defense (DOD) computer 

communications research program and were intended to allow easy exchange of data within the US 

Research and Military community. They became the premier standard mainly because they wor ked well and 

were readily available through the Unix operating system. 

The var ious networ k IP numbers are inserted onto the first diagram next tothe hosts and LAN segments 

(subnets) to which they apply. The quad-dotted IP numbers are like telephone numbers, they allow you to 

refer to subnets and individual connected devices, such as PCs, printers, routers. Each device is allocated a 

globally unique 32 bit address number, which is normally written in quadruple dotted notation. For my 

workstation, called olveston, the IP number is written as 164.11.253.36. This is actually: 

10100100000010111111110100100100 in binary, summar ized in hex for mat as: A40BFD24 . You can see 

the advantage to having friendly names such as milly and kenny allocated to each computer! 

In 3p11 the host numbers are allocated to the PCs in this way: 

164.11.222.01, 

164.11.222.02, 

164.11.222.03, and so on. 

Note that the left hand "164.11" is the University domain address on the internet. The "222" is the subnet 

address for the Netlab LAN, and the righthand, least significant numbers such as "02" refer uniquely to 

individual computers. Asalready explained, hosts are normally referred to by name, such as kenny or milly. 

The official name and IP number can be used interchangeably in most circumstances 

Find out the name and IP number of your current wor kstation by usinghostname -i orifconfig, 

(on XP useipconfig). 

Youcan trytesting for other hosts on the net by usingping. Ping also tells you how long it takes for a 

packet toreach its destination. 

rob@kenny> ping milly 

PING milly.cems.uwe.ac.uk (164.11.11.13): 56 octets data 

64 octets from 164.11.11.13: icmp_seq=0 ttl=253 time=0.6 ms 






ˆC 

--- milly.cems.uwe.ac.uk ping statistics --- 

7packets transmitted, 6 packets received, 0% packet loss 

round-trip min/avg/max = 0.5/0.5/0.6 ms 

rob@kenny> 

4. Logging out 

Use [CNTRL/ALT/DEL] and selectlogout for nor mal exit. Don’t turn off the power because then it takes 

longer for the next student to log on. Don’t forget to logout! There is a screen/key-lock facility if you want to 

pop out to the loo. 

4

5. Unix basic commands 

All self-respecting computers have a program called the Operating System to organize the facilities, protect 

the hardware from ignorant/malicious programs and generally help the user to have a good time. Unix is one 

of the most stable Operating Systems currently available. Sun’s Solar is, HP/UX and Linux are three well 

known versions of Unix. Most of the fastest wor kstations have been designed to run Unix because of its 

facility to deal with multi-processor hardware. Windows has not yet demonstrated long-term success in this 

niche, itisalso some-what cramped by the 32-bit Pentium, whereas the newer 64-bit CPUs (Alpha, ARM, 

HP/PA, Itanium) are already running Unix. 

Unix is a tool kit. There are hundreds of commands and tools to help the knowledgeable programmer. Many 

of the original, cryptic command line tools have now been repackaged for the X-windows and so are 

conveniently GUI-based. To stop a Unix process (a running program) try using[CNTRL C]. This usually 

works, else you must identify its process number, using theps command, and use this withkill. 

ls director y file listing,ls -al for more details 

ls list current directory 

ls -al ~ detailed listing of home directory 

ls / list top level, root directory 

ls -al Projects list contents of subdirectory, Projects 

ls /tmp/*.ps list names of all PostScr ipt file in /tmp 

cat ormore list contents of a text file 

mkdir ~/Newdir create a new subdirector y 

rmdir 

cd /tmp change current wor king director y 

rm junkfile remove/delete a file 

cp oldfile newfile copy afile 

mv oldfile newfile move a file 

pwd pr int current wor king director y 

hostname pr int host name,hostname -i for IPnumber 

ps list processes,ps -AF for all processes 

kill pid kill a process 

man kill Help from Unix about thekill command 

xclock & display aclock, releasing the keyboard 

find ~ -name prog.c -print find a file 

grep -rs "marks" ~ locate any ofmyfiles referr ing to marks 

date 

wc file.txt letter, word & liner count 

whereis xeyes locate an executable 

file something test the file-type of a file called something 

So, boot up a PC into Linux, start the X windowing system if necessary from the command line by typing: 

startx,then use the RMB to select shells->xterm from the main window panel. This allows you to startup 

command windows and type in commands to Unix. Try these example commamds: 

ps list your processes with PID number 

ps -FA 

hostname -i; hostname -d 

/sbin/ifconfig -a another way to find out your local IP number 

xeyes & star t xe y es inthe background, note the "&" 

ps 

kill xxx inser t the PID number for the xeyes process 

xeyes & 

kill ‘ps | gawk ’/xeyes/ {print $1}’‘ anice Unix pipe 

xhost + 

5

6. Printing 

xterm -T kenny -n kenny & 

change to new window 

ssh -X yourid@kenny 

Password: ******* 

export DISPLAY=3p11-10.netlab.cems.uwe.ac.uk tell kenny your screen 

emacs & 

(find . -name "fred*" -print >> ~/foundit ) >& /dev/null & 

background search for a file called fred-something 

grep -rs "strncmp" /usr/include 

search for a function definition in header files 

ypcat passwd | grep -i "williams" 

using the Unix NIS/yp password file, locate a student 

When you want to print from a Linux system on the networ k, you can uselpstat to check printer 

availability,lpq to check the queue length, andlp to send a file to the chosen printer. The printers owned by 

ITS use the Pharos billing system which requires you to pay per sheet. A document to be printed is queued 

at the print station until you go and specially login at the station and release the print job. Uselprm to 

remove your job waiting on a printer’s queue. 

rob@kenny> lpstat -p 

printer bw_plain is idle. enabled since Jan 01 00:00 

printer col_plain is idle. enabled since Jan 01 00:00 

printer netlab is idle. enabled since Jan 01 00:00 

printer staffcol is idle. enabled since Jan 01 00:00 

printer staffps is idle. enabled since Jan 01 00:00 

rob@kenny:~$ 

rob@kenny> lp -dnetlab world.c 

request id is netlab-159 (1 file(s)) 

rob@kenny> 

rob@kenny> lpq -Pnetlab 

netlab is ready and printing 

Rank Owner Job File(s) Total Size 

active rob 160 client.c 8192 bytes 

rob@kenny> 

The following is a useful command line for printing wide, commented source code. Look up the manual page 

(man enscript) and find out what each of the 7 flag options achieve . Note that it should all be typed into 

Unix on a single line. You could use this for your programming assignment listings. 

enscript -dnetlab -c -r --header=’$n|%W|Page $% of $=’ -n2 

-Dduplex:false -fCourier10 prog.c 

7. Remote access 

Students maybeable tologin to the Unix hosts or wor kstations from anywhere, through broadband or 

through dial up modems. Remote sessions via the Internet are routed, for security reasons, through a firewall 

host. To use this facility for inward remote login, you will have to register with the Help Desk and obtain an 

ssh password. I login from home using the secure shell (ssh) command: 

rob> ssh r-williams@gateway.uwe.ac.uk 

r-williams@gateway.uwe.ac.uk’s password: 

Then I telnet or ssh to milly to see my files, orssh to kenny for Netlab access. You cannot achieve much on 

the gateway machine itself, but it does run the ftp demon, so it can act as a forwarding station for off-site file 

transfers. 

6

The utilitynslookup can be useful when you are trying to find domain names or IP numbers. Check out the 

manual page for nslookup, and try:nslookup yahoo.co.uk. Itcan be useful when trying to set up a 

session from home to know some IP numbers. 

yahoo.co.uk 217.12.3.11 

blueyonder.co.uk 62.30.31.86 

google.co.uk 66.249.93.104 

milly 164.11.11.13 

kenny 164.11.222.253 

kyle 164.11.222.164 

nas 164.11.8.48 

The two applicationstelnet andssh provide remote login capability. But if you want to transfer files 

between computers there are several alter natives which can be exploited, besides the flash stick, of course. 

8. Flash sticks 

•dual login and use desktop cut & paste facilities to copy text across 

•ftp or sftp (file transfer protocol) 

•NFS file expor t/sharing 

•web browser such as IE or Firefox using http and SAVE AS the file 

•email an attachment to yourself 

To use a flash stick, CDROM or floppy inaPCrunning Unix, you have to notify the computer that a newfile 

system is available by using themount command: 

7

Inser t your flash stick, and use themount /media/flash command. On my machine the mount point is 

/media/DISGO due to some problems with its file system. Then inspect the flash stick director y using:ls 

-al /media/flash. Remember toumount /media/flash before removing it from the computer. The 

reason you have to tell the system when you intend to withdraw the memory stick isthat often the new data 

is held in RAM cache, and not immediately written to the flash memory. Thus you have to flush the cache 

before removing the stick. Watch the flash stick LED for activity. Unix also has thesync command to flush 

all buffers before turning off the power. 

In large networ ks, itiscommon for data and executable binaries to be distributed amongst several hosts. 

This is made possible by the Networ k Filing System (nfs) provided by Sun Microsystems. This allows a user 

to see remote files as if they were stored on the local hard disk. Microsoft offers a similar facility known as 

"shares". To get an indication of the usage of the nfs cross-mounting facility use thedf -k utility, which 

gives more infor mation thanmount. Below ispar t of the df -k results for my wor kstation: 

rwilliam@olveston [87] df -k 

Filesystem kbytes used avail capacity Mounted on 

/dev/hda2 34177192 3261124 30916068 10% / 

tmpfs 254096 0 254096 0% /dev/shm 

/dev/hda3 8770392 4 8770388 1% /shared 

tmpfs 10240 700 9540 7% /dev 

nas:/nas 1756463104 215384496 1541078608 13% /nas 

/dev/hdc 620876 620876 0 100% /media/cdrom0 

rwilliam@olveston [88] 

Youcan see mention of the partitions on the local drives hda2 and hda3, also the remote mounted nas 

device which expor ts its file systems to all the local computers for access. This makes them appear the same 

as locally stored files. Note also the last entry which shows a removeable CD (Burks) has also been mounted 

for access.Inlarge sites, files are distributed across many different computers. But more and more, user 

data files (home directories) are held on a Networ k Attached Storage (NAS) device which efficiently 

manages terabytes (T, 2 40 ,or10 12 )ofstorage. 

9. Unix & MS Windows-XP in P,Q&NBlock 

There are several distinct subnets and computing labs set up in different lab blocks. You must get used to 

their differences and individual quirks if you want to gain the maximum benefit from your time at university. 

Take a stroll around the campus site to locate the different labs. 

The ability for Unix to handle data for Windows, using the SMB file server program means that a single host 

can store files for both Unix and XP. Atthe moment a large ( 1.7 TB) networ k storage array perfor ms that 

function. 

10. X11R6, X-windows 

Unix originally did not have a GUI interface. Itcould only be accessed from the command line, through a 

command line interface (CLI), normally called the Shell. Now itisnor mal to install the X-windows suite of 

programs on top of Unix to provide full WIMP/GUI facilities. Itisimpor tant to understand that X-windows 

suppor ts distr ibuted processing in addition to a graphical display facility. 

If when you login, Unix does not automatically evoke the X11 GUI, you can often start itmanually with: 

startx. 

Nowadays, without X-windows, Unix looks ver y quiet and unexciting. This is the same situation you find when 

running a MicroSoft command prompt (C>) orDOS session. Occasionally you may have tolog into "vanilla" 

version of Unix. On Linux this is possible using the F1-F7 keys with [CNTL][ALT], but only one of these 

sessions can run X11, this is usually on F7. Try[CNTL][ALT]F2. Login to a parallel session and checkon 

your processes. You should be able to see processes from the previous processes. Logout and hit 

[CNTL][ALT]F7 to return tothe X11 session. X-windows often involves 3 separate processes: an X Client 

application, a Screen Server, and X-window Manager. The client application is the user program that wants 

to displaysomething. The Screen Server runs the .... screen, rendering the display correctly under the 

control of X protocol packets. Finally, the X-window Manager organises multiple window sessions on a single 

screen, taking events and directing them to the correct client processes. There are several alter native 

8

managers: twm, olwm, kwin, 

Pr int Ser ver 

client 

application 

Window 

manager 

Screen Server 

X-windows Client-Server couplets wor king across a networ k 

Note that the Client and Manager proceses do not need to be running on the local machine. Infact, it is 

common to distribute X applications around the networ k, in order to exploit the available processing and 

storage facilities. With such a powerful and flexible system, there is a real danger of unwanted data arriving 

on your screen. The first level defence is to stop all "foreign" hosts from sending data to your screen: 

$xhost - 

This stops all the fun! So normally you would open up to trusted remote machines or friends: 

$xhost +kenny +rwilliam +164.11.222.164 

With this arrangement, new windows can be opened on your machine from anyone running on kenny orkyle, 

or rwilliam from any machine. 

If you are running a client X application (in fact practically any Unix program) and wish to display remotely, 

the client process has to send X data acros the networ k to the selected target screen. This can be done be 

setting theDISPLAY environment var iable on the client machine: 

$export DISPLAY=target_machine:0.0 

The term target_machine can be either the IP or the domain name of the machine This will of course mean 

that all o/p will get redirected tothe same remote machine, soanalter native istouse an X command line 

parameter when starting the application: 

$xeyes -display 164.11.253.36:0.0 

Following this introduction to parameters for X applications, there is also font control. 

$emacs -font -*-helvetica-*-r-*-*-*-120-*-*-*-*-*-* & 

The font name is too complex totype in, even though only 3 of the fields are necessary. Use the font browser 

xfontsel to view the available fonts, copy the name specifier using the [select] button, and paste it back onto 

the command line using the middle mouse button. 

$xfontsel & 

9

11. KDE desktop environment 

The K Desktop Environment, usually abbreviated to KDE, is one of several graphical desktops for Linux. The 

main alternative isGnome. Generally, desktop GUIs offer everything you need to wor k with on a daily 

basis.But occasionally you still need to use the command line to obtain the required facility. The typical KDE 

desktop consists of several par ts: Apanel at the bottom of the screen, used to start applications and switch 

between desktops. Itcontains the K menu, a large icon which displays a menu ofapplications which start 

when LMB clicked. A taskbar, bydefault running across the bottom of the screen, is used to manage 

currently running applications. Click onanapplication on the taskbar to switch to the application. The 

desktop itself, can display icons for frequently used applications. KDE provides multiple desktops, each of 

which has its own windows. Click onthe numbered buttons on the panel to switch between desktops. 

Applications can be started by: 

Selecting a desktop icon, 

Selecting the name from the main KDE menu (botton left corner), 

Typing the name into a command window, such as konsole or xterm. 

Typing the name into the Tool Bar Application Launcher window, 

RMB click ondesktop, select Run. 

KDE is constructed using the Qt X-windows widget librar y, and comes with many useful X applications, such 

as the browser Konqueror, Konsole terminal, Kpackage package manager and many more. Anon-line help 

system is available from the toolbar as a life belt icon. This shows the KDE help files as well as the normal 

UNIX man pages. The Linux HOWTOs are also available on kenny at/usr/share/doc. 

12. Unix BASH shell 

AUnix shell, such as bash, sh, csh, ksh or tcsh, is a program which monitors the command line keyboard 

input, interprets the instructions and outputs results to the screen. It runs when you start acommand 

window (konsole or xterm). Because everybody’s prompt is different in this sheet we will try touse the old $ 

sign as the Unix prompt. Note that you can change your line prompt if you want to, when using the bash 

shell: 

$ 

$ export PS1="hi> " 

hi > 

The user interface program, or Command Line Interface (CLI) isknown as the shell. There are several 

alter native shells that the user can choose from: 

sh original Bourne shell, written by Steve Bour ne 

csh C shell written by Steve Joy 

ksh Kor n shell, often found on HP equipment 

tcsh tennex shell, my favour ite 

bash born again shell, used with Linux 

10

Just type inksh orbash to swap toanother shell. You can return tothe previous shell withexit. The 

bash shell is often found running on Linux and is like the old Bourne shell. It does things a bit differently to 

the csh, so to change your bash screen prompt you need to type:PS1="here> ". Onthe ksh the same 

would be You may find a short prompt is preferable. 

Some shells offer helpful facilities for users, such as auto completion, command line editing and 

command line history. Iuse bash, tsh or ksh to get command line editing in the style of the emacs editor. 

histor y auto editing 

list previous next completion 

bash history ˆP ˆN TAB emacs 

tcsh history ˆP ˆN TAB emacs 

csh history !! TAB ed 

!-1 !emac 

!42 

!mkd 

sh TAB none 

ksh fc -l r 

histor y fc -e emacs 1 

ksh -o emacs histor y ˆP ˆN TAB(Linux) emacs 

The character erase key can sometimes get lost. It can often be bound to either [DEL} or [BS}, you can set 

erase to whatever you want: 

$ tset -e[BS] 

$erase set to Cntrl-H 

$ 

Another feature of Unix is the PA TH. This "environment var iable" holds a list of directories where 

programmes can be found. 

rob@kenny> printenv PATH 

/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:/usr/games:/usr/local/ 

jdk1.3.1_01/bin:/usr/local/mysql/bin:/usr/local/samba/bin:.:/opt/ 

gnome/bin:/usr/share/texmf/bin:/usr/openwin/bin 

Adding another bin location to the PATHlist: 

rob@kenny> export PATH=${PATH}:/home/netlab/rob/bin 

rob@kenny> printenv PATH 

/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:/usr/games:/usr/local/ 

jdk1.3.1_01/bin:/usr/local/mysql/bin:/usr/local/samba/bin:.:/opt/ 

gnome/bin:/usr/share/texmf/bin:/usr/openwin/bin:/home/netlab/rob/bin 

If you trytorun a program and Unix gives the error "not found", it might mean that the program isstored in a 

director y which is not mentioned in the current PATHlist. If you already know where the executable is stored 

on disk you can simply sort itout by typing in the full pathname, such as/usr/sbin/ping, oradding the 

director y to your PATHlist,setenv PATH=${PATH}:/usr/sbin, Ifhow ever you have no idea where in the 

CEMS NFS networ k the code might reside - you have a bit of a problem! Removing an entry from the PATH 

is a bit more sophisticated, involving command piping and substitution which we will encounter again, later in 

this wor ksheet: 

$ printenv PATH 

/usr/bin:/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin/:/usr/games:/home/rob/bi 

$ export DISPLAY=‘echo $PATH | sed ’s#/usr/games:##g’‘ 

$ printenv PATH 

/usr/bin:/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin/:/home/rob/bin:. 

Or you could just use the command line editing facilities to achieve the same amendment. 

11

At Unix log in, you used always toget an American joke, or "fortune cookie", but unfor tunately solemn Sun 

have removed this important facility from their Solaris distribution. They probably think that jokes are 

inappropr iate for software professionals and not wor th the risk of litigation should someone take offence. 

An important feature of all shells, including BASH, is their capacity to handle short programs or scripts. This 

allows you to record instructions in a file and play them later; agreat asset for systems adminstrators. There 

are many uses for this which you will discover. Here is an example of searching for another PC which has 

been powered up on the LAN: 

$ hostname -i 

16.11.222.253 

$ 

$ for ((i=1; i do 

> ping -c1 164.11.222.$i | grep "64 bytes from 164.11.222.$i" 

> done 

64 bytes from 164.11.222.11: icmp_seq=1 ttl=255 time=4.02 ms 









$ 

The whole script can be recalled with a [CNTL P] and will re appear as 

$for ((i=10; i

13. Unix HELP facilities 

The traditional source of online infor mation 

for all Unix systems is the collection of 

manual pages. These are notoriously 

daunting for beginners. Try typingman 

mkdir for infor mation about how tomake 

anew director y. Ifyou only have a "subject" 

and need to locate relevant man pages you 

can use the keyword search: 

man -k subject. 

In fact, most programmers rarely read all 

the words in a man page, only scanning 

through for example code fragments. 

Occasionally however you do need to 

spend time and read the obscure text, 

especially with reference to control flags 

and directory names. 

Sun, to their credit, offer the Answer Books which are an excellent source of online infor mation about Unix, 

Solar is in particular. The Linux Documentation Project (TLDP) has a wonderful set of useful manuals and 

also it maintains a set of shorter, practical notes called HOWTOs: 

or 

http://www.tldp.org/HOWTO/ 

http://www.linuxhowtos.org 

The Student Help Desk may provide students with introductory help sheets about a var iety of software, 

including Unix and PC topics. 

The main source of up-to-date infor mation is the WWW. Computing students do spend a lot of time using 

Google,browsing for sites offer ing useful infor mation. Big companies, such as Intel, Microsoft, IBM and HP 

take some trouble to support their own products, but also offer general guides. Many universities, especially 

in the States are free with their course material. Try these now: 

http://www.ee.surrey.ac.uk/Teaching/Unix, from Surrey Uni. 

http://www.reading.ac.uk/ITS/Topic/UnixOS/UnSIntro01/, from Reading University 

http://8help.osu.edu/wks/unix_course/intro-1.html, from Ohio State Uni. 

http://par tmaps.org/era/unix/shell.html, focuses on the shell 

http://www-128.ibm.com/developerwor ks/linux/librar y/l-kdei, intro to KDE 

intro2unix.ps Fiamingo, DeBula & Condron, from 

ftp://www-wks.uts.ohio-state.edu/unix_course/ 

(Be careful when using web material in your assignments. Read the guidelines on how toavoid the 

accusation of plagerism (copying)) 

Sun additionally offer a set of online Help Handbooks. Click RMB (right mouse button) on the desktop 

background and selectHelp 

13

But there is no substitute for a good text book when you are struggling to understand and use new 

commands.Sodoget one as soon as possible. 

My personal favour ite is Paul Wang, but this currently out of print> Any suggestions for a decent substitute 

would be welcome. 

An Introduction to Berkeley Unix, Paul Wang, Wadsworth, 

Introducing Unix and Linux, Mike Joy, Stephen Jarvis, Michael Luck, Palgrave Books, 

Linux & Unix Programming Tools: a Primer, SSarwar, KAl-Saqabi Addison Wesley 

This LAST text at one time included 2 CDs with Linux Mandrake 8.2. I do not know ifthis arrangement 

continues. 

What you need is an approachable text, not too scary for beginners, but with sufficient infor mation and 

technical detail to last the course. 

As a Unix beginner you may get into difficulty, try the following sources of help: 

1. a friend who knows a bit more than you, 

2. Google for relevant advice, 

3. your lab course tutor, 

4. a Unix student text book, essential purchase! 

5. online Help pages, from the root menu. 

6. the Computer Officers who lovingly tend the Unix networ k, 

7. the online Unix manual facility: man ..... 

Forabit of history you can browse the following sites: 

14

http://www.computinghistor ymuseum.org/teaching/papers/research/ 

http://www.bell-labs.com/histor y/unix/ 

http://www.levenez.com/unix/ 

http://www.unix-systems.org/what_is_unix/histor y_timeline.html 

14. Using Windows-XP to access Unix 

1. Log into a Windows-XP PC , start upacommand prompt windows, displaying C> or similar. Then type in 

telnet orssh and the IP number of your local Unix server. 

2. A better alternative istouse the Xceed application. If you want to get through to Unix from a Windows PC, 

you may be able torun Xceed. Xceed offers full X-Window facilities, while telnet is limited to a simple 

command line interface. You will then have to use your Unix id and password to gain access to the Unix 

ser ver.When this happens you may concurrently run XP-windows side by side with Unix sessions. This can 

be confusing, with the local XP session running processes actually on the PC, while the X-window isonly 

displaying data, passed through the networ k from the Unix host which is actually running the process. 

3. A more sophisticated alternative istoinstall Redhat Cygwin software on the Windows-XP machine. This 

provides a Unix emulation ontop of Windows, allowing Unix applications to run, including those requiring Xwindows. 

15

15. X Applications 

The X11R6 windowing system is a ver y complex arrangement. A ver y clear introduction is available in the 

Wikipaedia site: 

http://en.wikibooks.org/wiki/Guide_to_X11/Introduction 

If the application program isspecifically written for X it could setup a new window onyour display. An 

advantage of a windowing system is the possibility of viewing output from several programs simultaneously, 

and copying text between the many windows. 

Cut & Paste between Windows The mouse allows you to copy text from window towindow 

without retyping. Drag the cursor across the text that you wish to copy with the LMB 

held down. Release LMB. Position the mouse pointer at target location and click CMB to 

paste in the text. This technique can be ver y useful in many situations, especially when 

you need to kill a process: 

Look in /usr/games. Try running /usr/games/kbounce &. You may position this by moving the pointer and 

pressing the LMB once. Ifyou wish to use the original xterm window again you must start the Xapplication in 

the background by typing an & at the end of the command before hitting [CR]. 

$ls /usr/games 

atlantik gnect gnotravex kbackgammon kgoldrunner kolf kshisen ktron 

banner gnibbles gnotski kbattleship kjumpingcube konquest ksirtet ktuberling 

blackjack gnobots2 gtali kblackbox klickety kpat ksmiletris kwin4 

fortune gnome-stones iagno kbounce klines kpoker ksnake kwin4proc 

gataxx gnometris kasteroids kenolaba kmahjongg kreversi ksokoban lskat 

glines gnomine katomic kfouleggs kmines ksame kspaceduel lskatproc 

$ 

$ /usr/games/atlantik & 

$ 

Youcan add the directory /usr/openwin/demo to your PATHand then only need to type in the name of the 

program, and not its full path: 

$ xeyes& 

xe y es: command not found 

$ 

$ setenvPATH/usr/openwin/demo:{$PATH} 

$ xeyes& 

$ 

If everything goes pear-shaped, and you want to start again, first kill off all your processes by clicking on the 

console window and typing: kill -9 -1, (minus nine minus one) and standing back aseverything rapidly dies. 

Youwill need to login again after such a drastic retreat. 

Another directory with X applications is /usr/bin/X11. This could also be added to your PATHlist. Type in 

Becho $PATH and see. Some applications are available from the desktop by pressing RMB on the root 

window (background). The resulting menu offers further option categories: Programs, Graphics, Inter net, 

Packages, Languages. Look through the var ious alter natives. The web browser Netscape is a good place to 

star t. 

16

Tr y some more X applications which are in /usr/bin/X11 or /usr/openwin/demo: 

xlogo &, totally useless 

xe y es &, quite fun for 3 minutes 

xbiff &, useful 

hexcalc &, you thought you had escaped from hex! 

psycho &, desperate demonstration for salesmen 

xfontsel &, useful Xfont browser 

worm &, horr id 

xfig &, you need to study for this 

xedit &, Istill prefer emacs 

xloadimage, nice to see some high class images, look in /pub/gifs/.... 

xmh &, mail handling prog 

xload &, keep a watch on the ethernet 

xman &, manual pages browser utility, could be useful 

roids &, shoot cosmic rocks before they collide with your space ship 

puzzle &, saves all those little bits of yellow not-quite-sliding plastic 

xtrek &, dubious benefit to mankind 

xkill, kills off x applications! 

rob@milly [46] ps -FA | grep rob 

rob 9713 1 0 Feb 17 ?4:07emacs -fn fixed -geometry 79x26+0+0 

rob 10991 8324 0 11:17:36 pts/110:14ghostview /tmp/rob.ps 

rob 15241 10991 017:54:42 pts/110:03gs -sDEVICE=x11 -dNOPAUSE -dQUIET -dSAFER - 

rob 9810 9713 0 Feb 17 ?0:00/usr/local/bin/ispell -a -m -B 

rob 8323 9160 008:29:47 ?0:09xterm 

rob 9160 9158 0 Feb 17 pts/00:01-tcsh 

rob 8321 9160 008:29:39 pts/00:04twm 

rob 8324 8323 008:29:56 pts/110:01tcsh 

rob 13970 1 0 Feb 17 ?0:15xbiff 

rob 15296 8324 1 18:02:18 pts/110:00grep rob 

$ kill 13970 

The process number (PID) can be wiped and pasted into position after the kill command to avoid typing in 

the number. 

$ ls 

prac1.pasprac2.pas 

$ pc pract1.pas 

$ ls 

prac1.pasprac2.pasa.out 

$ lpr -Pfx prac1.pas 

$ lpq -Pfx 

no entries 

$ 

lprm - This removes all your print jobs from the queue if you decide to 

save a few branches for later. nb: the negative sign / hyphen. 

mail Mail is a ver y useful Unix facility to send and receive messages, known as 

e-mail, throughout the networ k, or wor ld. At UWE an alternative mail system is 

used called simeon. 

cd directory_path Change directory allows you to move around the file 

system which is organized to look like the roots of a tree. 

cd / puts you at the ver y top of the hierarchy, use ls to see. 

cd puts you back home again. 

17

cd .. moves you upwards towards / (the file system root) 

Note that the tilde ~ character stands for your home directory, and if you want to refer to a friend’s home 

director y you can prepend the tilde character to their login id:~j2smith 

16. Writing C Programs 0n Unix 

To create a program you need an editor and a compiler. Use emacs as the editor and cc as the compiler.Fire 

up the editor, either from the desk-top menu bytypingemacs on a shell command line within an xterm 

window. (If you find emacs too scary/complex, Sun offer the alternative ofasimple text editor from the desktop 

menu) 

cc first.c -o first This compiles a c program stored in the file first.c and 

produces an output file called first in your current directory. Ifyou do not 

put in the -o first option, the output file will be named a.out by default. 

Star t up emacs, ifitisnot already running, and try atraditional first 

program inthe C language: 

main() 

{ 

} 

printf("Hello world ! \n"); 

** Emacs: wor ld.c 

The emacs commands which you need are: 

The Unix commands which you need are: 

ˆXˆW first.csaves emacs buffer into a disc file called first.c 

ˆXˆC exits from emacs back toUnix command level 

$ gcc first.c -o first compiles the C source file 

$ first runs the translated version of your program 

Av oid thea.out disaster by always using the friendly: -o 

There is a ver y good on-line web-based C tutorial offered by Brian Brown. 

Youcan down-load it yourself or access a local copy at: 

http://www.cems.uwe.ac.uk/~irjohnso/coursenotes/uqc146/cprogram/ 

18

If you have nev er used EMACS, aset of self teaching tutorials is provided, get into emacs and type: esc X 

help-with-tutor ial 

To enter a program inUNIX use the EMACS editor and then use the appropriate compiler to translate the 

source code into machine executable for mat ready to run. 

Cisevoked with cc ..... (the ..... is where the file name goes) 

or gcc .... 

Here is a C sorting program totry out. Note that it uses a function calledbsort which uses a librar y function 

calledstrcmp(). What do you think bsort does? What then is strncmp()? Use the man pages to help you. 

Be careful how you name your sort program. What if you unfor tunately happen to call it "sort"? Try typing 

sort on the command line before you compile your program. Get it? Unix already has a program called sort! 

So beware.Usewhich sort to find out which version of sort isbeing chosen to run. 

#include 

int bsort(char* pc[ ], int n ) { 

int gap, i, j; 

char* pctemp; 

for (gap = n/2; gap > 0; gap /= 2) 

for (i = gap; i < n; i++) 

for(j = i-gap; j>= 0; j -= gap) { 

if (strcmp(pc[j], pc[j+gap])

17. Web page 

First make sure that you have a subdirector y called public_html in your home directory. Ifnot, insert one with: 

makdir ~/public_html. Then change the access permissions:chmod 755 ~/public_html. 

At this point you can take acopy ofsome valid html to get your home page started. Try using this framework: 

 

My personal page 

 

 

My Personal web page 

 

 

Stuff about me 

 

Or get this one in a web browser : 

http://www.cems.uwe.ac.uk/~cduffy 

Now select [View] -> [Document source] and you will see the html source code which the browser interprets 

to generate the previous screen. Edit the html for your own use and save it asmy_page.html in the 

public_html subdirectory inyour home directory. Then make sure that the file permissions are set for others 

to READ-ONLY, chmod 644. Now check that it renders successfully in a web browser. The URL will be: 

http://kenny/~your_login_id 

20

This page will not yet be available for viewing outside the UWE domain. 

 

 

Craig Duffy’s home page 

 

 

Craig Duffy’s Home Page 

 

 

 

 

Send email to me. 

My machine is: staff 

 

 

 

 

Course handouts and details 

Application Programming in Visual C++ Assignment 2 Computer Networks and Operating Systems UQC109S2 Embedded Systems Programming year 2 UQC113S2 Advanced Operating Systems Programming UQC152H3 Real time and Embedded Systems Programming Final year UQC122S3 Embedded Control Systems Programming Masters UEE072HM Introduction to Operating Systems UQC155S2 Application Programming in C++ UQC157S3 Software Design and C++ UFS003C2 System On Chip course Individual project (Computing) UQC120D3 ****** Project Viva Timetable June 1-2 2006 ******

Some More Readings: 

’Essential EMACS’ help sheet is available, followed bythe more detailed GNU emacs manual. 

Another lengthy wor ksheet on using EMACS is also available. 

There are many brilliant books on Unix for students and exper ts, you must get one as 

soon as possible to help you through this course. Try either of the following: 

’An Introduction to Unix’ by Duffy C. Char twell Bratt, 2nd Ed 

’An Introduction to Berkeley Unix’ by Wang P. Wadsworth 

’Getting Started with UNIX and X’ by Andreasson T. &Skansholm J. Addison-Wesley, 1993 

22

THE ESSENTIAL EMACS 

To enter EMACS (gmacs) screen editor type: emacs 

When using X windows type: emacs & 

NOTES: i) The CONTROL key is represented by ˆ,use like the shift key 

ii) The ESCAPE key is represented by {ESC}. 

The ESCAPE key must be released before the command character is pressed. 

iii) The BACKSPACE key is represented by {bs}. 

------------------------------------------------------------------------------ 

Ba ckwar ds Forwa r ds 

ˆB Char ˆF 

MO VE: {ESC} B Word {ESC } F cur sor moves on same l ine 

ˆA Line ˆE 

Upwar ds Dow n wa rds 

ˆP Line ˆN cur sor moves to new l ine 

{ESC }V Screen ˆV cur sor moves to new screen 

{ESC } < File {ESC } > cur sor moves to file end 

----------------------------------------------------------------------------- 


{bs} Char ˆD del ete cha rac ter 

DE L ETE : {ESC } {bs} Word {ESC }D del ete wor d 

Line ˆK del ete to end of l ine 

Block ˆ@ . .ˆWmar k star t of block wi th ˆ@or ˆsp 

mo ve the cur sor to block end , 

de l et e bl ock wi th ˆW 

----------------------------------------------------------------------------- 

YA N KBACK : ˆY res tor eswor d/l ine /bl ock 

pr eviou s ly del eted 

{esc }Y rol ls bac k through yan k queue 

----------------------------------------------------------------------------- 

FI LEHANDL ING : 

ˆXˆW . ..filename . . :file you r text inaname d di sc file 

ˆXˆF . ..filename . . :ge t aname d file int o EMA CS for edi t ing 

ˆXˆS :save you r fileont o di sc and con t inue ed iting 

ˆX I ...filename . . : inse r t ano the r di sc file at cur sor pos i tion 

----------------------------------------------------------------------------- 

ON L INE HELP : 

ˆH ˆH :hel p al ter nat ive s , ˆG to ret urn 

------------------------------------------------------------------------------ 

UN I XTEMP ORARYESCA P E fo r non -X peop l e: 

ˆX C or ˆZ :temp o ra r ily drops out of EMA CS int o anew she l l, 

re tur n wi th ˆDor fg, used when comp i ling , 

------------------------------------------------------------------------------ 

ASSOR TED : 

ˆG :abo r t the cur ren t comm and 

ˆL :re fresh the screen 

ˆX2 :sp l it screen i nt o two windows , 

comm u te betwe e n wi ndows with ˆXO (ot her ) 

{ESC } Xshe l l :conver ts the window int o a comma n d shel l , 

ve r y use ful ! 

{ESC } Xaut o-fi l l :se t wp l inewrapp i ng 

{ESC } 75 ˆX f :se t righ t ma r gi n to col umn 75 

------------------------------------------------------------------------------ 

EX I T: 

ˆXˆC :ex i t fromEMA CS 

------------------------------------------------------------------------------ 

23

ON-LINE UNIX MANUAL PAGES. 

Use the man command to get infor mation on UNIX things: 

$man pc 

$man man what????? 

$man sort 

sor t(1) sor t(1) 

NAME 

sor t -sor t files 

SYNTAX 

sor t [options] [+pos1 [-pos2]]....[-o output] [-T directory] 

[file...] 

OPTIONS 

The default is to sort anentire line. When more than one 

key is specified, sort executes the keys inthe order they 

are given. 

-b ignores leading blanks, spaces, and tabs in field 

compar isons. +pos1 should be specified with the -b 

option. 

-c checks if the input file is sorted according to the 

order ing rules. This does not produce any output 

unless the file is out of sort. 

-d specifies only letters, digits and blanks are to be 

significant. 

-f folds upper case letters onto lower case. 

-i ignores the characters outside the ASCII range 

040-0176 in nonnumer ic compar isons. 

24

THE ESSENTIAL Vi 

To enter the vi screen editor, gotoanxter m window and type: vi 

NOTES: i) The CONTROL key is represented by ˆ,use like the shift key 

ii) The ESCAPE key is represented by {ESC}. 

The ESCAPE key must be released before the command character is pressed. 

iii) The BACKSPACE key is represented by {bs}. 

The vi text editor has two modes. Itcan either be in text insert or command mode. Note that vi puts tilde 

characters down the lefthand side of the test window tomar k the position of empty lines in the text buffer. 

When vi starts up it is in Command Mode, soyou need to just pressibefore entering text. 

If you want to append text to an existing buffer, useainstead ofibefore entering text. 

Te xt 

inser t 

mode 

esc 

i 

Command 

mode 

Yo u stee r the cur sor abou t in Comma n d mo d e by key i ng one of sev era l spec i al cha r s: 

------------------------------------------------------------------------------ 


h Char l or use arrow key s 

MO VE: e Word b cur sor moves on same l ine 

Upwar ds Dow n wa rds 

k Line j or use arrow key s 

----------------------------------------------------------------------------- 


x Char de l et e charac ter 

DE L ETE : Word dw del ete wor d 

Line dd de lete cur ren t line 

d$ de lete to end of l ine 

Block ma . ...d’ a ma r k start of block , 

mo ve the cur sor to block end , and de lete 

----------------------------------------------------------------------------- 

In Comma n d mo d e you can enter Tex t Mo d e us i ng : 

Re t ur n to Comma n d Mo d e from Tex t Mo d e : 

i - inse r t tex t before the cur ren t cu rso r po s ition 

I - inse r t tex t at the beg inni ngofthe cur ren t line 

a - append tex t af ter the cur ren t cu rso r po s ition 

A - append tex t at the end of the cur ren t line 

o - open s anew l ine for inpu t be l ow t he cur ren t line . 

O - open s anew l ine for inpu t abo ve the cur ren t line . 

es c - ret urn to comma n d mo d e 

----------------------------------------------------------------------------- 

BLOC K MO V ING ma mar k star t of "a" block 

y’a takes a copy o f block f rom ’a to cur ren t 

----------------------------------------------------------------------------- 

SEARCH 

/wor d sear che s fo r wo r d 

----------------------------------------------------------------------------- 

YA N KBACK : 

Y copy l ine int o yank bac k bu f fe r 

yw copy cur ren t wo r d int o yank bac k bu f fe r 

25

y$ copy rema i nde r of l ine int o yank bac k bu f fe r 

yˆ copy start of l ine to cur ren t into yan kba ck buf fer 

p yan ks bac k de l et ed i temafter cur sor 

P yan ks bac k de l et ed i tembefor e cu rso r 

----------------------------------------------------------------------------- 

FI LEHANDL ING : 

:w filename . . :file you r text inaname d di sc file 

:r filename . . :ge t aname d file int o EMA CS for edi t ing 

:s :save you r fileont o di sc and con t inue ed iting 

------------------------------------------------------------------------------ 

UN I XTEMP ORARYESCA P E fo r non -X peop l e: 

sh : temp o ra r ily drops out of vi int o anew she l l, 

re tur n to vi by typ i ng "ex i t" 

------------------------------------------------------------------------------ 

ASSOR TED : 

es c :abo r t the cur ren t comm and 

/wor d :sea r ch for wor d 

------------------------------------------------------------------------------ 

EX I T: 

:ZZ :save fi le and exi t from v i 

:q :qui t 

:q! :qu i t, wha tev er 

------------------------------------------------------------------------------ 

Icer tainly prefer emacs to vi, but there remain some who think emacs makes life way too easy for serious 

programmers: vi is for real. Try enter ing your CV into vi, then type it in again to emacs. Ithink the latter will be 

aless painful exper ience. 

26

Introduction to Unix and Networks

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