PC Plus HelpDesk - issue 238
|This month, Paul Grosse gives you more insight into
some of the topics dealt with in HelpDesk
From the pages of HelpDesk, we look at:
- Audio CDs and CDROMS;
- NumLock status, BIOS passwords and keyboards;
- Trackerballs - high precision mouse;
- Browser security warnings;
- Linux User Groups;
- Better long downloads with wget;
- Browser-based FTP - 'get'ting;
- FTP on the command line;
- UNIX-like-OS file systems; and,
- Burning CD ISOs with K3b.
Audio CDs and CDROMS
On some UNIX-like
operating systems (some suffer from this and others
don't), you might find that you have some trouble
ejecting the CD or CDROM from the device using the eject
option on a drop-down menu.
As far as reasons go, the main suspect is that the
disc in the drive was mounted as an Audio CD and you are
using a shortcut that is for a CD ROM (as in the
screenshot). CDROMs are block devices (as are other data
storage devices such as hard discs and so on) whereas
Audio CDs are character devices. If you have a block
device in there, you might not be able to unmount it/
eject it by using the eject option on a character device,
even though it is on the same piece of hardware.
One solution is, say you already have a link for a
CDROM, to have a link for an Audio CD as well (and vice
NumLock status, BIOS passwords and keyboards
On many computer
keyboards - especially desktop keyboards - the arrow pad
on the right, turns into a number pad when the NumLock
light is on. As there is already a set of arrow keys
between the right hand set and the normal, qwerty part of
the keyboard, it makes sense to have the NumLock set so
that it is on when you start the computer up - this being
set by the BIOS.
It is also tempting to do the same with a BIOS on
laptop. However, this can become a problem if you already
have a password set. When you next boot up, you need to
type in the password so that the BIOS can recognise it -
if you have a keyboard similar to the one on the right, a
P will end up as a *, an O as a 6 and so on.
You can overcome this - if you must have the NumLock
on on a laptop - by typing a new password for the BIOS.
Take the NumLock off to type in your current password, if
you need to and then, put the NumLock on to type in your
new one. It doesn't matter if you have a password that
ends up with numbers in it such as 'killkilo' (which
would end up as '25332536') because you can remember it
by the keys you press ('killkilo') rather than the
numbers that it produces - as long as you don't change
keyboards to one that has a different alignment or no
overlap at all.
As the number lock on a laptop only has a use if you
are typing in large numbers of digit-only sequences, I
would recommend that you don't set it on in the BIOS in
the first place.
Trackerballs - high precision mouse
main problem with a mouse is that when you want
to click or double-click, you are applying a
force to the same device as what you used to
position the mouse pointer in the first place. It
is inevitable that when you apply the relatively
heavy, repeated pressure that is required to
double-click, you will move the mouse to some
extent because the mouse's job is to measure
small movements relative to the surface it is on.
people try to squash the mouse hard against the
mouse mat but that uses a lot of force and, as a
result, can strain your forearm.
The tracker ball on the right (it's so good
that I use it all of the time) does a better job
for a number of reasons:
- The aiming/positioning part of the
tracker ball (the ball itself) is
separate to the buttons - clicking the
buttons does not move the ball at all. In
fact, you can pick up the tracker ball or
slide it along the desk surface without
it altering the position of the mouse
cursor. In this way, you can position the
mouse, take you thumb off the ball and
then do what you have to do with the
buttons. This also makes double clicking
easier as well.
- The whole thing fits well into your right
hand - it just rests on it and all of the
components are in the correct position.
- Moving the mouse cursor around on the
screen requires fine motor movements. We
have already learned to write at school
and have that type of precision in your
thumb - here you move the mouse around
with your thumb. With a mouse, you use
your forearm. Just think what your
handwriting would be like if you held the
pen stiffly in your fingers (or fist) and
used your forearm to produce the motion.
Also, by using your thumb, you are not
tensing up your forearm by trying to make
it do these fine movements - we've
already seen that you can move the
tracker ball around the desk surface
without altering the position of the
mouse on the screen.
- This type of tracker ball has an optical
image on the right is a close-up of the ball. The
sensor work in the red/infrared region and
therefore to it, it looks like a white ball with
black spots on it.
Non-optical mice and
trackerballs use little wheels that grip the
surface but if your kids have been at the ball
with greasy fingers your you have eaten some
crisps, you can get grease on this ball without
it affecting its performance.
The light sensor doesn't see the grease and it
doesn't have little wheels that are trying to
grip it - the little dots are detected anyway and
your mouse performs normally.
Browser security warnings
are essentially three situations that warrant
warnings on browsers with regard to sending
information and the security of the connection.
- Sending information in the clear (on
http, anybody can read your data if they
have a packet sniffer - anybody between
your computer and the server)
- Switching from http to https (going from
in-the-clear to encrypted - https wraps
the http data in secure sockets layer
(SSL) encryption which uses public key
cryptography to exchange session keys and
is reasonably secure unless you are using
a browser that has been emasculated by US
export license restrictions)
- Switching from https to http (going back
to in-the-clear which would normally not
be a problem unless it is a result of bad
can see in the screenshot what a sample of http
network traffic looks like using Ethereal - a
network traffic analyser or 'packet sniffer'.
programs are perfectly legitimate and are very
useful if you are trying to make sure that a
network is running properly or if you are trying
to find out if somebody or something is up to
something on your network.
However, they can be used to observe network
traffic in order to spy on people so, like
everything, it is a double edged sword.
In the screenshot, you can see a packet from
Google and this demonstrates just how open http
traffic is. If it was https, there would be just
a page of gobbledegook.
Closing the door
So, if you want to protect yourself, what can
you do without?
If you are just doing some casual browsing
using a search engine, you will probably not be
bothered about any of the information going in
the clear. However, if you are doing online
banking, you will want to know that you are using
One thing to bear in mind is that some web
designers seem to think that you can start off a
session using https you can then go over to http
and it will be safe. This might have as the
reason behind it, the fact that it takes more
processing to deal with https so, get them in on
https and then, when nobody is noticing anything,
switch over to http.
The security of going back to http, as you can
see in the screenshot, it totally unfounded as
any details in http can be seen - http and https
are sessionless - the protocol used for the
previous pages have no bearing on the security of
the current page.
So, if you never type anything of any value to
anybody, you can turn off these warnings. If you
do use https, you will need to keep the warning
that you are going over to an insecure connection
(https to http) simply because you cannot trust
the assumption that every web designer has an
appropriate understanding of security.
Linux User Groups
If you are thinking
of moving over to Linux or you have installed it and need
a little help with something then you can contact your
local Linux User Group (LUG). There, if it is anything
like the one in Derby, you will meet people who have been
using it for years and have a knowledge of larger,
non-Windows systems as well as complete beginners.
You can find them LUG home page here and a
list of regions here.
Most LUGs have their own mailing list but the is a list
of specialised mailing lists - relating to particular
Better long downloads with wget
Downloading a large
file just by clicking on a link in a web page is quite
simple as long as it works. The problems arise if: the
download is particularly large (so it needs to have
near-perfect performance over a longer, continuous time);
the connection has a lot of contention (there are other
people competing for your bandwidth); your machine has to
compete with others on the LAN (more crowding of a
limited bandwidth); and you have a limited download size
If you are trying ot download an ISO or two (or more)
then these large files which are usually around the 600MB
size, can seriously eat into your download allowance or
at least frustrate you if they fail at some stage
(usually towards the end of the download). One other
problem is that you might want to download a number of
these files - one after the other - and you cannot sit
around for hours, clicking on links.
WGET is a program that will download files using a
number of protocols, either from the command line or you
can use a URL list in a file. It will also, if you want,
spider a site, using hyperlinks so that it can download
the whole site. It obeys the robots.txt files so
shouldn't provide a headache to server admins. You can
also control the way it downloads them so that it doesn't
clobber a server. Being able to run from a batch file or
a crontab/scheduler, if can be made to work automatically
so that you can download that large ISO in the early
hours of the morning so that the contention is better and
there are less users online.
You can get wget (if it didn't come with your system)
from here (the main page - http
or here (the download mirrors page) and if
you are running Windows, from here.
When you run wget, it lets you know what is going on
and how far it has got. It also keeps a log file if you
want so that you can see what has happened if you have
been downloading overnight (or if you went to the
shops/down the pub or something).
Browser-based FTP - 'get'ting
of us have used ftp with a web browser to
download files and the anonymous login is handled
transparently by the browser. However, if you
need to log in on an account that you have, using
a UserID and password, you will find that the ftp
server is not particularly helpful - usually
saying that you have no access rights. This is
because you typed in just the IP address or
domain name. Non-anonymous ftp needs more than
Say that your account name is 'joe90',
your password is 'PaperW8' and the IP address is
just gives you an error. If you type the
UserID, followed by an '@' and then the IP
you will then be prompted for a password in
the same way that you would if you were logging
into a password protected http account - the sort
of dialogue box you see on the right.
you are in, the account name will be in the
address bar as in the screenshot on the right.
can also add the password on the address line.
Using our example above, it appears like this...
However, whilst this is perfectly all right
for using automated logons using something like
wget where you don't interact with it; and your
browser will accept this type of login (ie,
without making you type the password into a
dialogue box), you might, depending upon the
browser you are using, end up with it, along with
your UserID, on the address bar after you have
logged in (some browsers take the password out
when displaying the successful URL).
One thing is certain however, and that is the
fact that your password will be remembered by the
address bar dropdown list on some browsers. If
you click on the down-arrow on the right of the
address bar, you will get a list of all of the
addresses (including account names) that have
been typed in manually. Some browsers also save
and display the password.
FTP on the command line
|Win98SE ftp client into a Linux box
|NetBSD ftp client into a Linux box
Most operating systems have an ftp client. Even
Windows 98 has one. As ftp is well established and the
client programs work on many platforms, the general
command set is pretty much the same.
Essentially, with ftp, you log onto a server, navigate
around the viewable file system, upload and download
various files and then log off. There are many other
things you can do but these are the commands that you
will need to use the most. If you want to use others,
just look up ftp in the help or manual pages or go online
and look it up on the Internet. One other way is to run
ftp and type help at the ftp prompt. You will see a list
of the commands and their important options. If you type
help and the name of the command, you will see its help
In the screenshots, you can see a typical ftp session
(the top one is using the ftp client in Windows 98SE and
the bottom one is using the ftp client in NetBSD). On the
command line, enter 'ftp'. Next, at the ftp command line
('ftp>'), you need to open the account on the server
so you type 'open address' where the address is either
the domain name or the IP address of the server you want
to contact. In this case, it is a local ftp server at
192.168.1.254. When it has connected, it will give a
welcome message and then a error/success code, in this
Next, it asks you to log in with your UserID and then
your password. If all is well, you will be told that it
is. You are now logged in.
You can work your way around the file system using the
CD command in the same way that you would if you were
navigating around a Windows/DOS or UNIX-like system. To
go down a level, type 'cd directory' where directory is
the name of the directory you want to go to. If you want
to go up a level, type 'cd ..'. If you want to go up a
level and then back down one, type 'cd ../directory'.
You can see what is in a directory by asking it to
list its contents. This is either done with 'ls' or with
'dir'. You can use either on the same system.
You can navigate by typing ls and then cding to the
directory you can see. This is sometimes easier than
trying to remember full paths and then making a mistake.
One other feature is that you can press the up arrow
key and get previous commands.
When you upload a file (ie you copy a file from the
computer you are on, to the server that you have logged
into), you effectively 'put' the file there. So, to put a
file, just enter
at the ftp prompt. If it is in the current directory,
you can leave out the path. This will copy the file from
your machine to the remote one, leaving it in the current
directory on that machine, using the same file name that
it had on the machie it originated from. You can specify
a different name if you want.
Downloading is pretty much the same as far as the
command line goes. In this case though, you are getting
the file so your command line looks like this...
which, like put, will keep the file name the same and
drop it in the current local directory. Again, you can
change the name if you want.
To log off, just type 'bye'
If your remote machine doesn't have an ftp server on
it but yours does, you can log onto the remote machine
using telnet or (better) ssh and then ftp back the the
machine you are actually sitting at. However, if you do
this, you must remember whether you are getting or
putting because you will now be looking at the transfer
from teh other side.
UNIX-like-OS file systems
is much apprehension from people who have had no
experience of UNIX-like systems such as Linux,
that they will not be able to navigate their way
around the file system. suppose the question is
'can you navigate your way around a Windows file
Most of the time, users will just want
to stay in their home directory - it has
everything there that they need: enough space for
their files along with any personal settings and
Also, other users cannot change their files
because of the way that the security on the file
system works. The only time you need to look at
the rest of the system is if you need to do some
However, knowing what is where can help if you
are doing something new.
In the screenshot, you can see a real
UNIX-like operating system's file system. This
one is from OpenBSD - the others have the same
basic directories and structure.
|So, here are the main points of interest on
the file system
directory from which all others are
based. There is no C: drive or anything
like that, this is better and simpler
directory contains the executable files
(binaries) that you are likely to type in
at the command line yourself. eg 'ls',
'grep', 'chmod', 'mail', 'more',
'ps','su', 'vim' and so on.
directory, there are all of the devices
that are on the system. For example, on
some systems, the first hard drive is
called 'hda' (the second 'hdb' with 'hdc'
being the CDROM, 'hdd' being the next
hard drive and so on.
partitions so the first partition of the
first drive is called 'hda1', the second
is 'hda2' and so on. So, the path to the
second partition of the first drive is
directory has the configuration files in
it. Unlike the Windows registry, if you
mess up a configuration file inhere, only
that part of the system won't work. In
here you will find some directories for
the more complex parts of the system and
a number of file ssuch as fstab and so
|In the home directory,
you will find the directories of the
normal users. Each user has a unique ID
and that ID is the name of their
directory. The directories that are found
inside their home depends upon what the
user is doing and what programs they are
using but you will usually find a /bin
directory (for their executable files
that are not for other users - they could
be writing a program) and if they are
using a GUI,a desktop directory ... and
directory is where devices are mounted
from /dev. If, for example, you looked at
hda1 - the first partition of the first
hard drive, you would see the file
allocation table and the clusters of data
- assuming that it was a FAT partition.
file systems are mounted, they are
displayed as files and directories.
You don't have to have a file system
mounted in /mnt, you can put them
root's home directory.. Nobody other than
root can go in here
where the system binaries are kept. These
are the executable biles that you are not
very likely to type at the command line.
They aare more likely to be called by
another system command or by the system
when it is going about its normal
|/tmp is the
temporary directory. This is where files
with a short lifespan are kept. Some
systems clear this directory out every
time the machine is booted and other
systems have a routine that is run one a
week or so that clears out any files that
are older than a certain date.
where any user-oriented executable files
are kept that are for all of the users -
as opposed to the files in /home
|An, this is
where the system binaries installed for
all users on the system - those not part
of the basic system.
many types of files but system files such
as logs and so on usually go in here. If
you are running a web server, some
systems will put it into the /var
/var/log contains the log
files for the system and some programs
have their own log directory in this
contains files such as email files and
printer files amongst others.
There are other directories on the main
'/' root directory but you wouldn't normally need
to concern yourself with these - arguably, you
would n;t with most of those above.
In the end, instead of having your home fall
under 'Documents and Settings\user' and then some
others under a different user with it all being
presented as though you are the only user on the
system as it does with Windows, you have all of
the files you want in your /home/user directory.
It couldn't be much simpler than that.
Burning CD ISOs with K3b
Burning a CDR with an ISO on a Linux system is very
straight forward. First of all, download your ISOs - if
you are burning a free operating system such as Linux or
one of the BSDs, you will likely have several ISOs to
burn so download them all first - using wget as above
possibly. If you have limited space on the machine you
are burning them from, download them to another machine
on your LAN and then you can transfer them across when
you need them - this only takes a few minutes for a 600MB
your ISO image in a local directory, just click
on the ISO file in Konqueror and K3b should open
up and the ISO should be the current file.
not, select K3b from the menu.
Next, click on 'Tools', 'CD', 'Burn CD Image'
- this is in the version of K3b that is with SuSE
9.2. The menu for the version of K3b that is with
SuSE 10.0 is very slightly different in that it
cuts out a menu stage.
Following this, you select the ISO image you
want from the usual load dialogue.
you have some options at the bottom of the form.
If you are trying out your CD burning for the
first time or are using a storage medium that
might be a bit on the slow side, you need to
select 'Simulate' Simulate will go through the
burning procedure without burning the CD. Whilst
this might seem pointless, it is checking that
the pipeline between the data storage and the CD
will all work throughout the duration of the burn
process. If the simulation fails, you need to
change something but you haven't sacrificed a CD
in the process.
The last checkbox - 'Verify
written data' is needed if you are burning an
ISO. Whilst the burn process is no different to
that without it, if there has been a mistake -
even just one bit (as in binary digit) - then
this will most likely pick it up.
Finally, Click on the 'Start' button. This is
effectively lighting the blue touch paper and
retiring to a safe distance.
you have asked it to simulate the process, it
will go through that first and if there are no
problems, it will start writing to the disk at
the speed it has worked out will work.
process may take some time depending upon the
burn speed and the size of the ISO (This one is
for a NetBSD Live ISO at 693.6MB so it is at
pretty much the limit of the CD.
it has successfully finished the burn (ie, it
didn't fail because of any buffers running dry),
it then, if you have asked it to, checks the
image that it has stored locally. It does this by
putting the whole file through an algorithm
MD5 will take chunks of data and
produce a number. If the data is changed in any
way, it will result in a completely different MD5
When you downloaded the ISO in the first
place, there was (or at least should have been)
an md5 hash of the ISO on the web site so that
you can compare your downloaded image with the
one that is on the website. If the md5 hash is
different, there has been an error in teh
download process. When K3b first loaded your ISO,
it started working out an md5 hash and if you
weren't too quick at pressing 'Start' it would
have displayed the value so you can check the
value without first burning the ISO to a CD.
it reads the data off the CD and works out the
md5 checksum of that.
If the checksums are
equal, it is reasonable to assume that the
burning process is a success.
This is why I say reasonable to assume rather
than a certainty: An md5 checksum is 32 nybbles
long (a nybble is 4 bits and is usually
represented by a hexadecimal digit) or 128 bits.
So, there is a 1 in 2128 chance that
two files will give the same md5 result. To put
that into numbers that mean something, that is
3.438 or if you burned an ISO that
resulted in a faulty CD, once every 10 minutes,
you would on average have to take
years (472,000,000,000,000,000,000,000 times the
age of the universe) before you got one that gave
the correct ISO but was wrong. Not too bad.
And that is all there is to it.
Back to PC Plus Archive Index Page