Introduction to Unix and Networks

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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
Page 1 and 2: Title: Introduction to Unix and Net
Page 3 and 4: login shell. It is recommened that
Page 5 and 6: 5. Unix basic commands All self-res
Page 7: The utilitynslookup can be useful w
Page 11 and 12: Just type inksh orbash to swap toan
Page 13 and 14: 13. Unix HELP facilities The tradit
Page 15 and 16: http://www.computinghistor ymuseum.
Page 17 and 18: Tr y some more X applications which
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
Page 25 and 26: THE ESSENTIAL Vi To enter the vi sc

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