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PC Plus HelpDesk - issue 240
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:
- SSH remote host change;
- Word counts in OpenOffice.org;
- CD installation-set recognition problem on
UNIX-like systems;
- Hidden files in UNIX-like OSes;
- Alternative uses for MP3 players;
- TCP FIN scan attacks;
- Configuring a DHCP server for a small
network;
- Configuring an SMB printer in SUSE 10.0;
- Webmin;
- BOGOMIPS;
- Open Source Software for Windows; and,
- PostScipt Sudoku answers from issue 239.
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HelpDesk
SSH remote host change
 If you dual boot
with a computer and both (or at least some, if you are
using more than two) operating systems support SSH
(secure shell - encrypted using public key cryptography
for key exchange) then, the fingerprint of the remote
machine (the dual boot machine) will change for each OS
that is used on there.
If you use Windows on that machine, you will have to
have installed an SSH server on there to be able to log
into it remotely but all grown-up operating systems come
with SSH as part of the distribution.
To solve the problem, just delete the lines in the
file that are identified in the warning. Here, the file
is in the .ssh directory. Just open it up in a text
editor and delete the lines, remembering to save the file
before you have a go.
You could work around this problem by hacking the SSH
configuration but there is a very good reason for it
coming up with this and that is that the warning is a
basic warning about man-in-the-middle attacks or people
trying to break into your system so leave it alone and
put up with it. If they want to break into a system they
will have to use another method (no system is completely
secure but that is no reason to go out to town and leave
your front door open) so leaving this in place will keep
all of the low to medium level hackers out.
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Word counts in OpenOffice.org
 The selected word
count in OOo2 is not situated in the Properties dialogue
box, it is under tools. This is (I presume) because
highlighting a portion of text and wanting a count of
those words is something that a hack like me - who is
trying to write to a set number of words - will want to
use regularly.
So, instead of typing [Alt]+[F], [I] for the
properties page, you need to type [Alt]+[T], [W] for the
'Tools'/ 'Word Count' page. Click on the image on the
right to see what you get.
Note that in Windows, the [Alt] key is sticky so once
you have pressed it, you can release it if you want,
before pressing the first key - in KDE, you have to hold
down the [Alt] key while pressing the first letter.
Whilst this might seem an advantage to Windows users, it
is something of a double-edged sword. Sometimes, people
press the [Alt] key by accident and don't realise what
has happened. Just imagine what happens if you type the
word 'ear' after having pressed the [Alt] key by mistake.
On a KDE system, you would get the word 'ear'. On
Windows, you would select all of the text and then
replace it with the letter 'r'.
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CD installation-set recognition
problem on UNIX-like systems
 If
you run a UNIX-like operating system such as
Linux or one of the BSDs, you could, once you
have everything installed the way you want it,
leave it running without rebooting it for months.
It is also likely that you won't install anything
for a long time as well.With this in mind, it
can come as something of a shock to you to find
that if you do want to install something, the
system won't recognise the CDROM with the install
sets on it. It doesn't matter how much you clean
the disc, it will not be recognised.
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 The
reason for this is that the CD ROM reader has sat
still for months, doing nothing. All that has
happened is that dust has been sucked through the
computer and where there is a shiny surface, it
has settled.The solution is to blow across it
to remove the dust. Ideally, you should use one
of the compressed air cans you can get in
hardware shops but if you must use your lungs,
make sure that your mouth is empty first as
removing saliva could be a problem if you can't
get at the lens.
On the right, you can see dust on this lens.
This could conceivably affect Windows machines
as well if you let them run long enough.
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Hidden files in UNIX-like OSes
 On Linux systems or
any UNIX-like OS including Mac OS X, OpenBSD, FreeBSD and
NetBSD, files and directories whose names start with a
dot are hidden by the system from normal operations such
as ls (directory listing).
To see these files, you need to be explicit so, in ls,
just use 'ls -a'.
In Windows, the hidden attribute does the same and, if
you are unfortunate enough to have been hit with the Sony
Rootkit Trojan, other files will be hidden as well.
In Mac OS X (which is very loosely based on FreeBSD
although it is more like Windows than BSD), there are two
other ways of hiding files:
- Being listed in the '/.hidden' file - so much for
keeping the root empty of files (a major faux pas
in UNIX circles as these should go either in /etc
or /var); and,
- Having the 'invisible' attribute set. This is
closer to Windows than UNIX.
In Konqueror - as you can see in the screen shot -
change the listing view with 'View'/ 'Show Hidden Files'.
You can see the same directory but one has the hidden
files listed.
So, why hide files? Most of the time, it isn't to try
to pull the wool over your eyes, it is simply to get them
out of the way in normal work. You don't want to see all
of your settings directories listed if you just want a
normal listing of your home directory. If you do want to
see them, doing so is easy, just as it is in DOS.
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Alternative uses for MP3 players
 If you've got an
MP3 player but don't always want to listen to music,
there are other things that you can use them for (and I'm
not thinking about things like door stops or for stirring
paint).
You can either rip your own resources such as CDs for
language learning or there are a number of mp3 resources
online. Here are a few:
- The BBC (http://www.bbc.co.uk/) has a
listen again feature that will allow you to
download some whole programmes as mp3 files
although you should be careful here as sometimes,
they will use RealMedia files instead (so that it
is streaming). There doesn't appear to be any
consistency here at the moment. Also, as a
television license payer myself, I wonder why the
BBC insists on paying royalties for mp3 files
that it serves when it could spend less by using
Ogg Vorbis instead (there is no royalty to pay to
any file format patent holder for using the Ogg
file format).
- Radio Lovers (http://www.radiolovers.com/)
has some good classics on it from a vide variety
of sources; and,
- Orson Welles' notorious broadcast of War of the
Worlds (amongst many others) can be found at http://www.mercurytheatre.info/.
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TCP FIN scan attacks
 Sometimes,
people claim that they haven't been spending as much time
on a particular program as they really have - this is
usually browsers or instant messenger programs.
Some online chat servers send TCP FIN packets after
the connection has closed and these can look to a
firewall like an attack. With a hardware firewall (and
some software firewalls), you can get it to send you an
email whenever this happens. So, when someone says that
they have finished half an hour before the firewall has
send you a message saying that they did, you can question
that legitimately. It is worth pointing out that these
apparent attacks (they aren't really attacks but the
firewall treats them as possible attacks so that you know
if you are really under attack) don't necessarily
represent the exact moment that a connection has been
dropped.
So, if your daughter claims that she finished on here
instant messenger at 10:30pm when she was supposed to and
you get an email like the one in the screenshot, you know
that you can say; 'Computer says; "No".'
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Configuring a DHCP server for a
small network
 If
you have started off with a small network and
used the hosts files on each machine, you might
start to find that as you increase the number of
hosts on the network, the amount of work involved
with keeping each host's hosts files up-to-date
increases very quickly. The quick answer to this
is to use Dynamic Host Configuration Protocol
(DHCP). In the screenshot on the right, you can
see a typical exchange between a new host and the
server.Virtually every machine expects to see
a DHCP server on it's ethernet connection and
therefore uses it by default. If you use KNOPPIX,
it will look for a DHCP server during boot up.
So, it would be very handy to have your own DHCP
server on your LAN.
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addresses but also permit you to have a pool of
addresses that are alllocated dynamically. Firstly,
you need to install the server which should be on
your distribution disc set. With it now
installed, open up a file browser and go to the
/etc directory. In there, you should now see a
file called 'dhcpd.conf'. The default file
usually has plenty of notes about how you do this
and that, showing how flexible it is but this can
appear complicated for a basic configuration so
copy it to the same directory and call it
something like 'dhcpd.conf.old'.
Load up the existing dhcpd.conf file and
delete the entire contents. Then, try the
following...
default-lease-time 600;
max-lease-time 7200;
ddns-update-style ad-hoc;
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.5.255;
option routers 192.168.5.254;
option domain-name-servers 192.168.5.254;
option domain-name "yourdomain.com";
subnet 192.168.5.0 netmask 255.255.255.0 {
range 192.168.5.50 192.168.5.80;
range 192.168.5.100 192.168.5.150;
}
host desktop1 {
hardware ethernet 00:00:DC:2E:A6:0D;
fixed-address 192.168.5.1;
}
host laptop2 {
hardware ethernet 00:00:DC:2E:A4:36;
fixed-address 192.168.5.90;
}
 This
specifies the network parameters the machine
needs and will give your machines a reasonable
lease time. The default lease is given when a
lease length is not requested whereas the maximum
lease time is given when it is.
In addition, we have specified two ranges of
IP addresses for the DHCP pool - from 50 to 80
and 100 to 150 in this case.
Also, we have specified the IP addresses of
two specific hosts by defining their Ethernet
addresses.
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 Start
the server in a console by entering/usr/sbin/dhcpd -d -f eth1
where eth1 is the interface in this case. Note
that if you are using eth0, there is usually no
need to specify the interface. The -d switch
makes dhcpd log to stderr so you'll be able to
see what is happening and the -f switch keeps
dhcpd in the foreground.
Boot up a machine on your network so that it
uses DHCP (a machine with a KNOPPIX disc will do
if you don't have one already configured to use
DHCP) and watch what happens in the console. If
it all works well (that is to say that you can
browse the network/Internet from the KNOPPIX
machine), press [Ctrl][C] to kill the dhcp server
and then start up dhcpd again without the -d and
-f switches by typing
/usr/sbin/dhcpd eth1
If you use eth1 or another interface and you
have found that you need to use it on the command
line, you might need to alter the runlevel dhcpd
file in '/etc/rc.d' so that the dhcpd run line
includes the interface. Note that
'/etc/rc.d/dhcpd' might not be on your system if
it boots up differently.
If you want to start it up by hand each time
you boot the server, just leave a note to
yourself in your 'bootup_readme.txt file on your
root desktop.
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Configuring an SMB printer in SUSE
10.0
If you have a printer already established on another
machine and that machine tends to be in use all of the
time, you can configure your Linux machine to use the
printer network share.
Note that for security's sake, you have your LAN
behind a firewall otherwise, other people will be able to
hack your Windows machines
 On the Windows machine (if it is
one), just enable network sharing and then, in
Windows Explorer, click on the Printer folder in
the tree in the left pane (under My Computer) and
then right click on the printer you want to
share.Next, select the 'Sharing' tab and
select the 'Shared As' option button. Next, type
in a share name (uppercase and no spaces is
usually a good idea) and anything else you want
to add to the other fields.
Click on 'Ok' and that is it as far as putting
it on the network is concerned.
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 On your Linux box, open up the KDE
'Control Center' and in the tree on the left,
select 'YaST2 Modules'/ 'Printer'.Type in the
SuperUser password at the prompt if you need to
(your don't have to have logged into a KDE
session as root to configure the printer but you
do need to be root whist you configure it).
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 Next, the configuration page
displays and it checks through its list. If this
is the first time, it will build up a database
which might take a minute. |
 In the next page, click on the 'Add'
button then select the 'Print via SMB Network
Server' option and click on 'Next'. |
 On the 'Connection Information'
form, you need to type the particulars of the SMB
server you need to use.When you have done,
click on the 'Test Remote SMB Access' button to
see if it is all right.
Then, click on 'Next'.
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 In 'Queue Name', give the name for
printing as something that is easy to type
because you might decide to do this using the
command line one day. Also, make the 'Printer
Description' fairly meaningful.Click on
'Next'.
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 In 'Printer Model', select the
manufacturer and Model of the printer you are
using.If you cannot find the specific one you
are looking for, you might like to try one in the
same series of printers as yours or, you can look
at the generic printers listed under 'unknown
manufacturer'.
If you know that a particular printer driver
exists and want to use that, you can click on
'Select PPD File'.
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 In the 'PPD Files' dialogue, you can
select specific driversYou can also test the
PPD files by printing a test page.
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 If you do print the test page, it
should look like this.With the correct
PostScript Printer Driver file selected, click on
'Next'
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 You should now see your printer in
the printer list. Click on 'OK'. |
 Now that to your configuration is
complete, click on 'OK'. |
 Next time you want to print
something, you should see the printer appear in
the printer list when you want to print a
document. |
 If you click on Properties, you can
change the printer configuration such as colour
depth and resolution. |
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Webmin
If you have a number of machines on your LAN that you
want to configure all remotely, you can do so using
Webmin.
 On
the local machine, you can use various
configuration files and programs to get the
system looking and working just the way you want
but if you want a central console from which you
have access to all of the machines on your LAN,
you need something that is designed to do the
job.Webmin allows you to configure hardware
and software as well as look at the status of
various system components. Not only does it do
this for the local host but is also allows you to
do the same for any host with a Webmin server
running on it. It does this through a standard
web browser running on any platform.
This program comes as part of the standard
SUSE install and is actually a web server and
some CGI scripts. Sections cover the local system
and servers through to hardware and clusters.
The program is available for many operating
systems and keeps on getting voted best system
administration program of the year and so on so
it is certainly worth a look - especially as it
is free.
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 Instead
of using Webmin just for configuration, you can
use it to monitor some components of a system. In
the screenshot on the right, you can see disc and
partition usage - you can also use it to look at
your mail. There are many uses of this program
and you can see more about it at http://www.webmin.com/.The
program is very cross-platform although for the
reason that each UNIX-like operating system uses
different locations for configuration files,
there is only support for systems that it has
been configured for. Straigtht from the Webmin
site, at the time of writing, Webmin (version
1.250) is supported by the following OSes:
- Sun Solaris;
- Lycoris Desktop/LX;
- Caldera OpenLinux eServer and Caldera
OpenLinux;
- Whitebox Linux;
- Tao Linux;
- CentOS Linux;
- Scientific Linux;
- Gralinux;
- Redhat Enterprise Linux and Redhat Linux
Desktop;
- AlphaCore Linux;
- X/OS Linux;
- Asianux;
- Haansoft Linux;
- cAos Linux;
- Redhat Linux;
- White Dwarf Linux;
- Slackware Linux;
- Xandros Linux;
- APLINUX;
- Debian Linux;
- SuSE OpenExchange Linux, SuSE SLES Linux
and SuSE Linux;
- United Linux;
- Corel Linux;
- TurboLinux;
- Cobalt Linux;
- Mandrake Linux and Mandrake Linux
Corporate Server;
- pclinuxos Linux;
- Conectiva Linux;
- ThizLinux Desktop and ThizServer;
- MSC Linux;
- SCI Linux;
- LinuxPPC;
- Trustix SE and Trustix;
- Tawie Server Linux;
- TinySofa Linux;
- Cendio LBS Linux;
- Ute Linux;
- Lanthan Linux;
- Yellow Dog Linux;
- Corvus Latinux;
- Immunix Linux;
- Gentoo Linux;
- Secure Linux;
- OpenNA Linux;
- SoL Linux;
- Coherent Technology Linux;
- Playstation Linux;
- StartCom Linux;
- Yoper Linux;
- Caixa Magica;
- FreeBSD, DragonFly BSD, OpenBSD, NetBSD
and BSDI;
- HP/UX;
- SGI Irix;
- DEC/Compaq OSF/1;
- IBM AIX;
- SCO UnixWare and SCO OpenServer;
- Mac OS X, Darwin and OpenDarwin;
- Cygwin;
- Sun Java Desktop System;
- Generic Linux; and,
- Windows.
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Yes, Windows.
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BOGOMIPS
 BOGOMIPS or bogus
MIPS is a measure of how fast the processor is and, like
any MIPS rating, it is open to abuse and misuse. It can
be used as an aid to get an appreciation about how fast a
given computer is but its primary reason for existing is
so allow Linux to function in a timely fashion where
timing is important.
To get to the BOGOMIPS value on a Linux box, just type
cat /proc/cpuinfo
Note that in order to do this, you need a /proc
directory so doing this on OpenBSD will not work as that
does not have a /proc directory - there are programs for
the BSD OSes though - see the link below.
If you are interested in this and run a Windows
machine, you can either run KNOPPIX and do as above or,
you can download the bogomips Windows executable which
can be found at http://hpm101.gotadsl.co.uk/projects/bogobinaries/.
Fave fun.
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Open Source Software for Windows
 Open
Source software is usually seen as being run only
on UNIX-like systems such as the many flavours of
Linux or the BSD family (other Unices are also
catered for). However, there are plenty of
projects that also have ports to Windows and DOS.Examples
include:
- OpenOffice.org;
- The GIMP;
- Firefox;
- Apache;
- wget;
- Webmin; and, so on.
Many of these have their own dedicated
websites but for the smaller projects - as well
as some of the larger ones - there are two main
repositories for the many programs either as
source that you can compile yourself or as
already compiled executables ready for whatever
operating system you have.
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 These
are Sourceforge ( http://sourceforge.net/
above-right) and Feshmeat ( http://freshmeat.net/
right). |
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PostScipt Sudoku answers from issue
239
If you have installed (if you needed to) a Post Script
reader of some sort and you have printed out and solved
the Sudoku problems I left you with last month, you might
like to know the answers to any that you had a problem
with. Click
here to open up the directory in a new window so that
you can see the solution files.
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