Introduction to Unix and Networks

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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 64 octets from 164.11.11.13: icmp_seq=1 ttl=253 time=0.5 ms 64 octets from 164.11.11.13: icmp_seq=2 ttl=253 time=0.5 ms 64 octets from 164.11.11.13: icmp_seq=3 ttl=253 time=0.5 ms 64 octets from 164.11.11.13: icmp_seq=4 ttl=253 time=0.6 ms 64 octets from 164.11.11.13: icmp_seq=5 ttl=253 time=0.5 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
Page 1 and 2: Title: Introduction to Unix and Net
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Page 9 and 10: managers: twm, olwm, kwin, Pr int S
Page 11 and 12: Just type inksh orbash to swap toan
Page 13 and 14: 13. Unix HELP facilities The tradit
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Page 19 and 20: If you have nev er used EMACS, aset
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Page 23 and 24: THE ESSENTIAL EMACS To enter EMACS
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