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10
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PC Plus HelpDesk - issue 217

This month, Paul Grosse gives you more insight into some of the topics dealt with in HelpDesk and HelpDesk Extra

From the pages of HelpDesk, we look at:

  • Web Statistics without cgi-scripts; and,
  • Voting without cgi-scripts.

From HelpDesk Extra, we look at:

  • Network Proxy Server Hardware;
  • Drive Partitions;
  • Software Packages;
  • Operating System;
  • Network Cards;
  • Firewall;
  • DHCP(C)D;
  • Proxy Server;
  • URL Filtering;
  • Network Addressable Storage;
  • Network Time Server;
  • Webserver; and,
  • Log Analysis and System Administration:
    • Ethereal;
    • Squid Log Analyser;
    • Webalizer;
    • KDE system Guard;
    • Info Center; and,
    • Nagios.
Paul Grosse

HelpDesk

Web Statistics without cgi-scripts

If you don't have access to webserver statistics for your website but do have a permanently-on connection to the Internet, you can collect your own statistics very simply. All you need to do is to run a webserver on your own machine - storing an insignificant image - and then have it displayed on some part of your web page. By doing this, the image will be downloaded by any browser that downloads images - ie most of them although you will not capture browsers such as links or those set up for blind people - and the details in your webserver log will hold their details.

The details you will have are the ones that they want to send you and if their browser is configured to send false information, you will have to put up with that as anybody would. However, most people don't know how to modify the information on their browser so you will get a representative set of data from this.

Ideally, you should have an insignificant image (might be just a line or block or even a completely transparent .gif file) that is part of the page you want to track. Put this in a directory of its own and you are part of the way there.

Now, all you need to do is to get a webserver on your system and the easiest one is Apache which currently runs around 67 percent of the world's websites.

Apache is:

  • free, so it is written by people who:
    • like writing computer code
    • are not doing it because they are the cheapest programmers around
    • do not feel that they are being exploited by a big company making big bucks out of them,
  • open source so any bugs
    • are found quickly by the biggest group of programmers on the planet
    • are not hidden by some company that wants to make its product look better than it really is
  • ... and
    • the programmers who write it know that their programming abilities will be scrutinised by people all over the planet and are therefore more likely to be careful by knowing that any mistakes will not be hidden by corporate proprietry secrecy
    • any patches or workarounds are sorted out quickly
  • popular - it has a large support network so:
    • if you have any problems, there are already people who have had the same problem and had it sorted out for them
  • not the most popular target for Internet attacks
    • In your access log, you will see many failed attacks aimed at IIS systems on Windows machines. If you are running your server on a Linux box, the attacks fail on two accounts. That is not to say that Apache running on a Linux box is not immune, just that it is not currently the target for a lot of attacks.

Once Apache is installed, all you have to do is change the httpd.conf file so that it knows where your webroot is and what to listen for (most of the rest of it is already configured for you although it is worth reading through it just to make sure - again, the answers to any questions are most likely already on the Interent for you). One additional change is to the type of access log Apache stores. In httpd.conf, there is a line which you need to change to...

CustomLog logs/access.log combined

if your logs are to be stored in a subdirectory called [ServerRoot]\logs (on Windows systems or [ServerRoot]/logs on a Linux system).

Once it is configured, start the server and then test it by running a browser and typing

http://localhost/[name_of_ image.gif]

in the address bar. If all is okay, (certainly as far as delivering the image is concerned), you should see it in the browser window. If you haven't got 'localhost' defined in your hosts file, you could just type

http://127.0.0.1/[name_of_ image.gif]

instead.

On your web page, you need to have your IP address and the path from your webroot. Suppose your server root (in a Windows machine) is C:\Program Files\Apache Group\Apache2\, your web root (relative to that) is \htdocs, your image is called img.png and your IP address (as accessible from the Internet) is 11.22.33.44. In your webpage, you should have the following...

<img src="http://11.22.33.44/img.png" hspace="2" vspace="2" width="16" height="16" Alt="Home Stats">

Home Stats

With your image in the page and your server up and running, all you have to do is to configure your firewall to allow port 80 (that is http) in from the Internet and you can start collecting that data. Note that you are doing nothing more than collecting the same data that everybody else does - you are not hacking into anybody's system. This data is sometimes used to provide browser-specific webpages on some servers so that if you have one of the more esoteric browsers, you cannot use their site unless you prefer text only content that is three months out of date.

To test out your page as it is on the Internet, you might find that you cannot type in its URL and see your image. If this is the case, it is because your browser is pointing back at a machine on your Internet interface. To get around this, you can do one of several things:

  • go to a friend's house and look at the page on his/her connection
  • use another connection on one of your machines (so that you have the broadband connection going to your webserver and another machine - possibly with a dial-up connection - going out via a different route. Make sure that you disconnect from your LAN the dial-up machine (or whatever method you are using to get out) or it will both defeat the object of the game and also allow access bypassing your firewall. You will also have to reconfigure the browser on that machine so that it goes out by a means other than your LAN connection - Tools/Internet Options ....
  • use a proxy. Go into Google and look for proxy browsers. Kallahar's Place is a good starting point. It will let you do this by going into Google and asking it to translate your page for you - if you have an English page, ask it to translate from German to English and it will fail on all (most) words, leaving them as they are. I say most because when I tried this, I have a subdirectory called /swf and it translated that into "Southwestern German Broadcasting Corporation" which was something of a shock as I had no such directory - hacking sprang to mind but was quickly discounted when I saw the path.

Your browser will think that Google is looking at your website. However, you will not see any images so you will need a html file for it to download (we are just checking that your server works - we already know what your image looks like) so put a file called index.html on the directory root and you will be all right.

An example of Webalizer output.
Click here to see the full-sized 
version of this image open up 
in a new browser windowOnce you have your traffic and your access log is filling up, you can use a program called Webalizer (there are a number of these programs but I have always found this one to do the job I need and it certainly fills your requirements) to analyse the access log. Webalizer will analyse the IP addresses and if you use the Linux version, will do a RDNS check and break down domains for you. It can do this in the Windows version but not always, I have found.

Your webalizer results will give you breakdowns of day of month, time of day, country, browser and so on. There is, of course, nothing to stop you from writing your own analysis program for your own purposes but the config file for Webalizer will allow you to tailor it to your needs faily well.


Voting without cgi-scripts

This is really just an extension of Web Statistics without cgi-scripts above. Again, not having access to cgi-scripts is not necessarily a bad thing as you can do it all on your home webserver (see Web Statistics without cgi-scripts above). On your voting page, you have your question and then links to small answer pages. At the end of the voting period, you get Webalizer to count the pages and you work out the results accordingly.

If it was a simple yes/no there is no problem. If you had a rating with, say, points from 1 to 5, all you do is add up the pages for the 1 point page, the same for the 2 point page and so on. Multiply the totals by their scores, divide by the number of votes cast and you have the result. You can also take steps to stop people voting more than once by only allowing the first vote (or the last) from a particular IP address or discounting them altogether (something to be aware of is that you can have networks of genuine voters hidden behind a single IP address).

Once you have your result, you can post it - do this on a weekly/daily basis. You can make your output graph as coarse or fine as you like or, you can cheat. The following is an example using a specific bar graphic.

Rate this site

Current rating
(updated 25/3/2004):
73%

There is an easier way that uses only three graphics (if you have one for 0%, 3%, 5%, 7%, 10% and so on, you have 41 graphics). Using tables, you can modify the length of the bar very easily.

eg.

    23%
    94%
    45%
    64%

This is done by having a table with four cells. The one on the right has the result in it, to the left of that, there is a transparent graphic which is set to the same image height as the bar images used (note that the height of this needs to be as large as the largest text you are going to use in the cell and also that it acts as a spacer). The two on the left have the images only as backgrounds but the width of the cells are set in pixels so that they two columns add up to 100 (the bar graph image is only 99 pixels wide and the other is even less but that is tiled - remember that images are tiled from the left). Of course, you don't have to make them 100 pixels wide in total, you can make them as wide or as narrow as you like.

The code looks like this...

<table border="0" cellpadding="0" cellspacing="0">
  <tr>
    <td width="23"
      background="images/bar_g_bar100.jpg">&nbsp;</td>
    <td width="77" 
      background="images/bar_g_bg.jpg">&nbsp;</td>
    <td><img src="images/8x8.gif" 
      align="middle" width="2" height="21"></td>
    <td>23%</td>
  </tr>
</table>

One thing that you will notice if you have a look at the files/webpage directory on the superdisk is that the html file that you get has a longer name than you might immediately think necessary - vote001-4.html for example. By doing this, you can have many votes over a long period of time and know what each refers to in the server log.

One thing you cannot do with this is have votes on multiple topics unless you either have them all on the same page with your users becomeing frustrated with always having to close browser windows; or, have a series of webpages that are linked to as they vote through a sequence of questions on new pages in the same browser - the html page name might reflect this like vt325.html preceded by vt32.html and before that vt3.html et cetera.


HelpDesk Extra

Network Proxy Server Hardware

Ideally, you should have a firewall between your proxy server and the Internet and it should be running on a separate machine all on its own. However, it is a good idea to have another firewall protecting the proxy server, running on the proxy machine as well as this can protect the proxy from the internal network in addition to anybody who breaks through your external firewall.

In additon to this, if you are going to have http accessible from the Internet, you should run this on a machine on a separate network (usually called a De-Militarized Zone or DMZ) so that if it is compromised, the intruder still has to break through another firewall before (s)he can get into your LAN. This last point means that if you are running processes that use cgi scripts (Common Gateway Interface), is should not be accessible from the outside because if that machine is taken over, things can be run on it that can compromise your network shares and so on.

Here, however, we will be running an Apache server with cgi scripts that is accessible from the Internal network and if you want, you can make it accessible from the external network by configuring the firewall to allow incoming traffic through port 80 (http) as well. To do this reasonably safely, you will need to keep the version up-to-date so that vulnerabilities are addressed.

In short, in an ideal situation, you would have three machines:

  1. Firewall (with three NICs - Internet, LAN and DMZ)
  2. Apache Server (with 1 NIC) in the DMZ (for the Internet and the LAN)
  3. Proxy Server (with 2 NICs) (between the firewall and the LAN with your Apache server running cgi scripts on it that is only accessible from the LAN

Here, we have 1 above (as an appliance with 2 NICs but you can run a software firewall on a dedicated machine) and 2 and 3 rolled into a single machine with 2 NICs (one facing the firewall and one facing the LAN). Note that the firewall on its own is not described here but setting it up is pretty much the same as the one described here except that you would not have any pull- or push-type connectivity with internal network resources (such as SMB - Samba) and so on (LAN hosts that use the proxy pull from the server).

If you just want to try this out or you are on a low budget, you can roll out all three in one machine. Running lots of services on your external firewall is not the safest thing you can do though.

So...

The idea behind this project is that you can speed up the effective Internet speed of your network so that if you have already downloaded a file and it has not been updated since, all that happens is that it is transferred across your LAN at speeds approaching 100Mbps instead of 600kbps or whatever your broadband connection speed is. To do this, you will need to have a spare computer or buy one for the purpose. In addition to this, you can use it for many other network related jobs such as firewall, URL filtering, network time and so on. So, what do you need to have (or buy)?

Computer

For small business purposes (unless you are running a busy website) you need only a modest machine. I managed to obtain a Fujitsu Siemens Sceneic X which had

  • 128MB RAM;
  • 6.1GB HDD;
  • 500MHz Pentium III Processor; and,
  • a built in NIC (as well as USB and all of the other stuff)

all for around 150 from a Derby electronics shop - there are plenty of these in University cities as students are on the lookout for such machines. You might want to take a copy of KNOPPIX on CD or CDR in order to check that Linux will recognise its components.

To this, I added a second NIC (a PCI card) to make it dual-homed and another 128MB of RAM and a KVM switch which meant that I did not need to buy another keyboard, monitor or mouse or find extra room for them. The Scenic fits under the existing monitor as the monitor's original CPU is a midi tower.

This setup is suitable for small businesses and homes so if you need really fast connection for some reason, you can buy more memory (the more the better), have a faster processor (or more than one - Linux supports this) or build your own.

KVM switch

The KVM I found was an ATEN 2 port KVM (50) which has built-in leads. If you are going to be unplugging the KVM a lot, it would probably be better to have one with separate leads as you can replace them when they break but for a static installation, one if these is cheaper. When pricing up these, remember that the leads are expensive if you have to buy them separately and you should therefore take that cost into account as they can cost more than some of the KVM switches.

The idea is that you plug both computers into the KVM and then your single mouse, keyboard and monitor into it as well (as you can see above). With this model, all you need to do is press [Scroll Lock] twice in quick succession and you swap from one computer to another which is quite handy although can be confusing. The LED indicator lets you know which connection is currently on so I would advise plugging the leads in so that this makes sense, ie the LED on the right implies the computer on the right.


Disk Partitions

Before you can install any software, your drive needs to be divided up in an intelligent way. Normally, with Windows systems, there is only one partition and the swap space is just a file in the only partition.

In Linux, this is done a little more intelligently with a minimum of two partitions - one for your files and one for your swap space.

It makes more sense to have a few more partitions so that things are protected. Things you might like to protect on a system are the boot partition (/boot in red on the right), the home directories (/home although this might be more like protecting the rest of the computer against what is going on in the /home directories), /var/log (the home of the log files (in blue on the right) - if this fills up, it does not clog up the rest of your drive), and so on.

Having your server directory on its own partition (/srv in green on the right) is often a good idea as well - anybody who gains access to your server and allows it to write to the partition that the server directories are on will only overwrite or corrupt that partition.

There are many ways of doing it and every one of them will have something wrong with it in somebody's eyes. Here, note that we are having some network addressable storage as well (under /nas but this is also used for the proxy (Squid) cache so I configured Squid to use half of it ie /nas/nas_cache for nas and /nas/squid_cache for Squid - I could have partitioned these separately if I wanted to but decided that if I found that I needed a lot of NAS, I could sacrifice some of the Squid Cache).

So, this is what I did and it seems to run okay. In the SuSE installation process, I divided up and partitioned the 6.1GB drive (as specified in the description from the shop) as follows...

Device Mountpoint FS type Size
/dev/hda1 /boot ReiserFS 71MB
/dev/hda2 swap Swap 439MB
/dev/hda3 / ReiserFS 3,514MB
/dev/hda4 /nas ReiserFS 4,032MB
Total 8,056MB

Notice that 8,056MB (7.87 GB) is slightly larger than the 6.1GB that Windows was getting out of the drive. You might be lucky and have this happen to you or you might not. This is, as far as I am aware, not a feature of ReiserFS.

Note that with earlier machines, there is a limit of 8.4GB on drive size. If you have one of these and it is down to the BIOS, you will not get more than the 8.4GB out of the drive regardless of the file system you use (ignoring compression).

Also note that ReiserFS has a very high efficiency for small files (it does not throw away the space at the end of a sector as FAT file systems do as it is designed to work differently to that) and if you are likely to have a lot of small files - such as if you are running a web server (all of those .gifs, .pngs and so on) - it makes sense to use ReiserFS. Also, ReiserFS is a journaling file system so if you have a dirty shutdown (such as power failure), it can get the file storage back together again in just a few seconds instead of several minutes - something that is important in an environment that is not tolerant of downtime.


Software Packages

Click here to open a new browser window at LinuxISO.OrgThe obvious choice for a server is Linux as this is well optimised for PCs (the PC versions anyway) and SuSE is particularly easy to install and use. You are not confronted with just a bare command line and you don't have to sit around for three hours while the kernel compiles. It installs quicker than Windows XP and only needs roughly the same amount of interaction as Windows XP during installation. I used SuSE Linux Professional 8.2 for this although the same principles apply for other versions and other flavours of Linux. If you want to compile everything yourself, you can use Gentoo or one of the others (the others also have pre-compiled versions as well).

These are the pieces of software that I loaded...

  • SuSE Linux (Operating System);
  • SuSE Firewall2 (Firewall);
  • dhcpcd (DHCP client daemon);
  • Squid (Proxy Server);
  • SquidGuard (URL Filtering);
  • Samba (for your Network Addressable Storage)
  • xntpd (Network Time Server);
  • Apache 1.3.xx (Webserver needed for Nagios - see below);
  • Log Analysis and System Administration
    • Ethereal (network analysis)
    • Squid Log Analyser (downloaded from Internet)
    • Webalizer (httpd access log analysis)
    • KDE system Guard (Monitor system load and network)
    • Info Center (keep track of resources such as memory and disk space)
    • Nagios (overview of whole network and beyond with automatic notification of any problems encountered)

NOTE: Wherever possible, I have opted for the GUI way of doing things instead of the command line (although I have given both in some cases) because this is the type of environment that people will be familiar with from Windows. Apart from just being able to click on things, the GUI also offers a visual representation of the system layout such as in Konqueror running as the file browser - something that should help with getting to grips with the system quicker.

Also, I have given the name and location of configuration files. To edit such a file, open up the Konqueror file browser (home) and locate your configuration file using the pane on the left (for directory structure) and click once on the file icon or name in the pane on the right to open it in Kwrite which is like notepad in Windows. You should of course, make a backup copy just to be on the safe side before you edit it (but remember to edit the current copy and not the backup).

With the exception of Squid Log Analyser, I configured the network cards (see 'Network Cards' below) and ran the SuSE system update which automatically downloads any patches that are required.

This ensures that your system is protected against recent attacks and vulnerabilities. As you have a broadband connection, this should not take too long although it has to be said that the first time you do it, it does take longer.


Operating System

SuSE Linux is very easy to install and installs quicker than Windows XP (I have done both). It uses a GUI (KDE, although you can use Gnome or a number of others) and takes you through the steps, explaining what you need to do (choose a keyboard layout, partition your hard drive and so on) and only took me 20 minutes on this installation (no office software although I did install The GIMP as I need to take screenshots so on yours, you should have more space and an even quicker installation).

KDE desktop under Linux. Click on here to load the full-sized image in a new browser window.When it is up and running, it looks like Windows and behaves pretty much the same. Linux was designed from the beginning to be networking so it works well at this and has a wide variety ot tools to make the job easier.

In the screenshot on the right, you can see the task bar at the bottom, the menu up the left (like the start menu in Windows) and a browser window open (Konqueror)

There are a number of tools available to help you and some of them are already on the taskbar.

On the right, you can see the icon with the Windows equivalent programs. Clicking on the K with the gears gives you the (Start) menu.

One thing you will notice is that there are multiple desktops. With these, you can set up a few standard desktops and leave them running. I use 'Info Center' and 'KDE System Guard' on two desktops, leaving them running.

You can configure the desktop - including how many desktops you want - by right-clicking on the desktop and selecting Configure Desktop. You can also do this with the Taskbar or, if you prefer, do them all from within the Control Center.

One thing you should consider is not having any screen saver other than 'blank' so that you are not occupying the processor unnecessarily. Also, you should set the time for screen saver activation to be only a few minutes. With a KVM switch, you are not saving a screen and also, you are not taking up space on your desk.


Network Cards

Before you can do anything network, you need to configure your network cards. Go into Control Center and then, YaST2 Modules/ Network Devices/ Network Card and configure the cards to your internal network and your cable modem.

In order to check that you have them the right way around, you can either connect the internal (LAN) card to a LAN machine and do something LAN with it or connect the external (Internet) card to the cable modem and launch a browser. If you have eth0 and eth1 identified correctly, this should work. If not, swap them over and try again. With the cards now correctly identified, mark them with sticky labels so that you don't forget.


Firewall

The SuSE Firewall2 comes with SuSE Linux and is a stateful inspection type within which you can activate Network Address Translation (NAT aka Masquerading). NAT does not a firewall make however, it is a useful addition as it makes it appear that every host behind it comes from just on IP address. The configuration file (SuSEfirewall2) is located in /etc/sysconfig

In it, you need to define FW_DEV_EXT, FW_DEV_INT, the external and internal NICs (although you can define any interface) and, if you have a demilitarized zone, you can define the interface to this as well - FW_DEV_DMZ.

There are a number of other options such as FW_MASQUERADE and FW_ROUTE and so on, allowing various degrees of functionality. The configuration file is heavily annotated and there is plenty of help about it on the Internet so your shouldn't have any problems setting it up by yourself.

If you just want to use NAT, you can set it up entirely from Control Center/ YaST2 modules/ Security and users/ Firewall. In fact, it is a good idea to start off with this anyway.

Once you have finished setting up your firewall, you can take the Internet connection and plug it into a local machine and then use that local machine to port scan it and attack it, just to see if it works properly.


DHCP(C)D

If you are going to use the machine as a dhcp server for your internal network, you need to configure and run dhcpd. dhcpd.conf (the dhcp daemon configuration file) is in /etc and there is support documentation in /usr/share/doc/packages.

If you need to request a dhcp lease from your ISP, you need to configure and run the dhcp client daemon (dhcpcd). dhclient.conf is in /etc and contains notes about its setup. More details are to be found in man dhclient.conf which you can get in the bash (Bourne Again SHell) console by typing "man dhclient.conf" at the command prompt or by going into the Konqueror web browser and typing "man:/dhclient.conf" if you have the KIO Slave installed.


Proxy Server

Squid is the name of the proxy server. It sits on port 3128, looking at requests for Internet http traffic from the LAN and when received, it checks to see if it already has an up-to-date copy of that file stored locally (ie, on your fast side of the modem bottleneck). If it has, it transfers that to the browser instread. Thus, if a website has been visited before and the files on the proxy server do not need to be updated, they can be downloaded at LAN speeds instead of the relatively funereally-paced broadband.

To use it, you need to change a line in the SuSEfirewall configuration file so that it says:

FW_SERVICE_SQUID="yes"

Squid's configuration file (squid.conf) is in /etc/squid. It is fairly long but almost all of it is annotation. It is worth working your way through it but the main parts are defining the port it listens to (say your internal network is 192.168.1.0/24 and its gateway is 192.168.1.254 and you want to listen to port 3128, you need the line

http_port 192.168.1.254:3128

and you also need to assign a space and location for the cache:

cache_dir ufs /nas/squid_cache 1400 16 256

is what I use signifying that roughly 1.4GB of /dev/hda4 is used for the proxy cache, leaving the rest for the NAS. Also set

debug_options ALL,1

for minimal logging.

Again, just work your way through it and when you have finished, start the service using Control Center - you will have to restart the firewall as well since you changed its configuration file. The easiest way to do that is with the command line but the most convenient if you want to avoid that is through the Control Center using the Runlevel editor - YaST2 modules/ System/ Runlevel editor.

The Runlevel editor allows you to select the run levels for any particular program. Run level 2 is a self-contained, standalone machine running just a command line. Runlevel 3 is the same but with network connectivity so network programs start to appear with this runlevel. Runlevel 5 is with the GUI. It also allows you to stop and start the programs and any that are dependent upon any others will be sorted out for you. Be careful with this editor as its consequences are very powerful. If you find yourself at a standalone command line on bootup log in as root and type

init 3

to set the run level to 3. To get the GUI, type

init 5

With squid running in runlevels 3 and 5, you should have your proxy service, albeit one that allows everything through without any filtering.


URL Filtering

URL filtering comes as SquidGuard. Its configuration file is squidguard.conf in /etc. This one is quite a bit simpler than the others although you will have to modify the squid.conf file so that it includes the line:

redirect_program /usr/sbin/squidGuard -c /etc/squidguard.conf

and to restart it, you need to restart squid.

Open a blocked page in a new browser windowFirst of all, you need to have a database of words, URLs and domains. You can download these from the squidguard website and install them in /var/lib/squidGuard/db. You can of course add to this list if you want to - see below.

Next, you can specify a redirect page for blocked websites. You can do this on the local machine web server - hence running Apache. You can make this as simple or complicated as you like. Click on the image on the right to see one thing that you can do with this (in this case for a domestic installation).... You can of course, put anything you like there or follow the example in the original configuration file.

One thing you will have to do is test it so you can go into Google and type "porn" (or whatever your restrictions suggest you should try). If all works properly, you should get the blocked page you have specified. It it does not, you will not be able to use that again without clearing out the local cache on the machine you are testing it on. If you don't want the bother of doing this each time, you will have to start clicking on the links and, as a result, downloading pages of porn.

Remember that you can turn off the images in the browser but also, remember that if anybody asks, you are configuring SquidGuard (which of course you are - this is not an excuse, this is a reason). If you want to preclude any unnecessary interest from your ISP or anybody else, you might wish to start the configuration testing by typing "SquidGaurd" into the search string before hand - of course, this is not guaranteed but it might help.

With SquidGuard, you can define access control lists by user, IP, time of day-week and so on so, if you want to allow your employees access to everything except porn sites, only during their lunch breaks whilst leaving the system administrator's machine unhindered by filtering at any time of any day, you can. Again, there is a lot of information on how to configure all of this.

Another useful thing that SquidGuard does is allow you to add your own words, URLs and domains to the blocked list. Apart from the obvious ones that you can block, you can also use your squid access log to find out the names of things you don't want to appear on your browsers such as advertising. If you look at your squid log, you will be able to see the names of websites that have been accessed and you can add these - either as full URLs or even just partial domains to the lists. In the future - after restarting Squidguard - they will not appear.


Network Addressable Storage

The idea behind this is so that you have some commonly available storage on the network. In this example, it is not protected but you can protect it with userIDs and passwords if you want: it depends on what user population you have. To get NAS working, you need to have samba installed and you also need to change a line in the SuSEfirewall configuration file so that it says:

FW_SERVICE_SAMBA="yes"

Samba is SMB which Windows uses and is configured by smb.conf in /etc/samba. You need to have the windows share you want defined and the level of sharing. Some lines have the same effect but the following should suffice:

[nas]
path = /nas/nas_cache
public = yes
guest ok = yes
create mask = 0640
directory mask = 0770
read only = no
writable = yes
locking = no

Restart samba in Control Center and it should appear in Windows Explorer under Network Neighborhood as above-right.

Remember to change the permissions of the NAS directory that you have allocated to UID nobody and GID to nogroup so that anybody can read and write them otherwise you will have to configure permissions.


Network Time Server

There is a saying that goes along the lines of 'A man with one watch knows exactly what the time is whereas a man with two watches never knows'. So, with at least several PCs it is a really nice idea to have all of the clocks on your network say the same time. A Network Time server will take the time signal from a suitable local second stratum time sever and not only keep its host's time correct but will act as a time server to other machines on your LAN. With only one machine querying the external time server, this will keep their traffic down.

xntpd is the time server and its configuration file (ntp.conf) is in /etc. There are details and help on how to configure it but if you put several external time servers in the list, it will find one that it can use and unlike some others, uses a drift file so that it can keep the machine's time accurate to within a few microseconds (it wouldn't really matter if it was just a few milliseconds really).

Just configure the time clients on your LAN machines to look at your server and they will all tell the time very accurately (ping times of <1ms are not uncommon).


Webserver

The Apache server (version 1.3.xx) is used by SquidGuard for its blocked pages and also by the network monitoring program Nagios (see below). We have discussed the configuration of Apache in the past (version 2.0.48 in PC Plus issue 213 - security cameras - hamstercam). Note that at the time of writing, the current version for version 2 is 2.0.49 and for version 1.3 is 1.3.29

Apache (httpd) is started and stopped from the Runlevel Editor and its configuration file (httpd.conf) is in /etc/httpd

Here you need to set the server name, server root and webroot. Then set any password restrictions on directories thus...

<Directory "/srv/www/htdocs/secrets">

AllowOverride AuthConfig
Options Indexes FollowSymLinks
Order allow,deny
Deny from all

AuthType Basic
AuthName "Secret Server Files access:"
AuthUserFile /etc/httpd/pswds
AuthGroupFile /etc/httpd/gps
Require group ssfg
Satisfy Any

</Directory>

You also need to create any password and group files listed in the restrictions, using the password program (see the documentation on its use) and kwrite to create the group files you need.

Click here to open up a new browser window at Apache's httpd project site.Your web pages will end up in /srv/www/htdocs and if you put a file in there called index.html, that will be displayed instead of a server-generated directory listing of your webserver root.

There is plenty of information about running Apache, both in the documentation that is installed with the server and also on Apache's website which is at http://httpd.apache.org/

Integrating SAMBA with Apache under Linux

One interesting thing about Linux is related to what you can do with disks and other resources.

In Windows, you are stuck with drive C:, drive D: and so on. If you want to refer to anything on another drive, you cannot do it without having to be clever.

With Linux (and other Unices) you mount a file system within the directory structure and it doesn't really matter what file system it is or even where it is.

If you look at the partition mounting tree above, you will see that we have mounted one partition as /var/log. This partition could be hda# or even a partition on a physically separate drive hdb#, hdc# or even sda# (where # is a number - hde5 for example).

In Windows, it is possible to represent network shares as drives and this is also true under Linux - except that it is not (in the same way that non- network drives are not) represented as a separate drive.

So, it is possible to mount an SMB share (from another machine, running Windows, say,) within the Linux system as though it was on the same machine.

In the example on the right, you can see that the partition mounted as /srv (yellow) has /srv/www/htdocs/hcam mounted in it. This is an SMB share from a drive on another machine on the network.

There are pros and cons to doing this. With the Hamster Cam/ Security monitoring (webcam) in PC Plus issue 213, we used a piece of software on a Windows machine that could ftp an image file onto a server every so often. Here, it is just saving it locally and when the Apache webserver wants a copy of it, it sends across the LAN a request for it.

If you are getting more hits per unit time on your server for this image than you are saving new images, the advantage lies with ftping (ie pushing) each new image to the server (remember that you would then have an ftp server running on it which has its own security considerations) whereas if you are getting fewer, the advantage is with using SMB to pull it across your network when required. This is based on the idea of keeping network traffic to a minimum.


Log Analysis and System Administration

In order to keep an eye on what is going on and to allow you to investigate things should you need to, there are a number of tools that you can use. The following are the ones that I find useful:

  • Ethereal (network analysis)
  • Squid Log Analyser - analysing the squid proxy log so that you can keep an eye on what is happening
  • Webalizer (httpd access log analysis)
  • KDE system Guard (Monitor system load and network)
  • Info Center (keep track of resources such as memory and disk space)
  • Nagios (overview of whole network and beyond with automatic notification of any problems encountered)

Ethereal

Ethereal is a packet sniffer. You can set it to look at either (or any) network interface (whether it is a NIC or a dial-up and so on) and it will observe any traffic on that network segment regardless of whether it was directed at the machines NIC or not - in other words, it views the network in promiscuous mode (although you can elect not to capture in this mode if you wish)

This program is useful for finding out what is happening if you are having problems setting up a particular program - for example, it could tell you what is going on if your dhcp negotiations are not working the way you think they should or if you want to check if something that should be encrypted is actually being sent over the network in the clear.

Squid Log Analyser

Squid log analyser (its configuration file is wherever you put the program) is a nifty little program from Olaf Schubert ( http://squidlog.sourceforge.net/ ) that analyses the access log file for Squid. You can configure it to look at the last however many entries you wish to check where the users have been and how many cache hits you have.

Click on the image on the right to see an example of the analysis.
The proportion of cache hits can vary depending upon what type of browsing your users are doing but I have seen the proportion of cached files in the last 500 vary from as low as around 20% to as high as 90%.

If your cache can be fairly substantial, say 1.4GB as on this machine, it can represent the casual browsing of an average family (read into that what you like) of several months worth of files.
One thing you might like to do with the code when you install it is to change one of the lines, just under the commented #date line there is a commented #convert UTC-Date... line and you should add another line (I did it just after $year=$year+1900;) thus:

$month=$month + 1; # correct the month

Webalizer

An example of Webalizer output.
Click here to see the full-sized 
version of this image open up 
in a new browser windowWebalizer is nifty little program that looks at your website hits and can give you an idea of just how busy your server is - certainly as far as port 80 is concerned. Its configuration file (webalizer.conf) is at /etc, is very well annotated and doesn't really need any explanation here.

It gives graphical output of the system including where on the planet the people who looked at your website came from, what time of the month and what time of the day, as well as letting you know which pages people entered and left your site on.

Each calendar month is broken down in this way so that you have the last 12 months at hand.

KDE system Guard

click here to display the full screenshot in a new browser windowThis program allows you to monitor the process table - a list of the processes that are at work which you can have as a simple list or as a tree - or a series of graphs which you can save and open later.

I keep a copy of this running at all times so that I can monitor what is going on. The default settings give you a 2x2 array of the top two rows of the screenshot. I have added another three rows with the LAN interface on the left and the Internet interface on the right (this is the way that it is arrange physically and it is always a good idea to do reflect the physical layout if you can as it makes more sense if you have to look at things in a hurry for some reason).

Of the bottom three rows, the top one is packets from the Internet to the LAN, the second is packets from the LAN to the Internet and the bottom one is collisions for the two interfaces.

You can see from the screenshot that there is a lot of traffic between the server and the LAN that is not going out to the Internet (I was hammering the LAN to test it by copying large files around it). On the bottom, you can see that the quantity of collisions decreases substantially as the interframe gap is increased by the NICs. The IEEE standard (802.3) says that it should be 9.6 microseconds but a lot of NICs have it set a lot lower than this because low demand networks such as home networks work faster as there are fewer machines on them to generate collisions. With more machines, you have more collisions so you should have a larger gap to help prevent this - note that you cannot prevent early collisions (ones that happen within the first 512 bits of data) as these will happen anyway.

Info Center

This is another one that I keep running on a desktop all of its own. Whilst it can tell you important information about your system such as how many bogomips it produces, it is more important to look at resources such as memory, storage devices (how the disk space situation is developing) and usb devices (if you are using any) as these are helpful in finding out how the system is changing or if it is nice and static.

If you look under Processor you can see how fast your processor is - the machine I obtained for this project gave roughtly 1200 bogomips

Nagios

This program runs on one of the machines on your network - some people say that it would be better to have it running on a machine on its own as it can take up a lot of processing power if you have a large network (possibly thousands of machines running many times more services) and frequent checks but for a small network of half a dozen computers to several dozen it should be okay to run it on a 500MHz machine with a few hundred MB of RAM.

The program itself monitors system resources by testing them at specified time intervals. The time intervals can occur at any time of the day or week or you can define your own working week with different days, hours and so on so, if a machine was only turned on during office hours but not on Wednesday afternoons, that could be defined so that it would know not to look for it out of the specified hours.

If something out of the ordinary happens such as a machine becomes unreachable for more than a specified amount of time, the program can email you or perform one or more of a variety of functions as specified by you in the configuration files - such an event could be triggered by a system crash, a hardware failure such as a NIC going down, workmen cutting through a fibre-optic cable or somebody stealing a server; and you would know either in real time or by looking at the logs when it happened.

Like the testing, the notification time periods can be specified so that people who are not available at weekends are not emailed during them and so on.

Nagios is capable not only of looking at the machines on your network, but also at other resources so if, for example, you have an outsourced website that you need to know is available 168/52, Nagios can check it for you and let you know if it was unavailable for eleven hours between Saturday night and Sunday morning although it cannot tell you why.

When you install Nagios, and then look at the configuration and help files (/etc/nagios) you might find that the paths are slightly different to some of the various Nagios resources on the system.

On mine, the webserver root (that is placed in Apache's server file system using aliases) is on /usr/lib/nagios; the documentation and other resources are on /usr/share/nagios; and; the ever-useful log files are on /var/log/nagios.

When you are configuring Nagios, you will find the log files very useful as they will let you know where you have gone wrong (unless you are exceptionally brilliant at it and manage to configure it correctly the first time you use it).

There are two main parts to configure:

  1. Apache
  2. Various Nagios configuration files: hosts, services, relationships between them and so on.

Apache

Look in Apache's configuration file - httpd.conf in /etc/httpd and in the aliases section, you need to let Apache know that Nagios is to be a part of the system and what it is going to be called...

Aliases section
## start of nagios inclusion
ScriptAlias /nagios/cgi-bin/ /usr/lib/nagios/cgi/
<Directory /usr/lib/nagios/cgi/>
  Options ExecCGI
  
  AllowOverride AuthConfig
  AuthType Basic
  AuthName "Nagios Access"
  AuthUserFile /etc/httpd/pswds
  AuthGroupFile /etc/httpd/gps
  Require group nagiosgp
  Satisfy Any
  
  order deny,allow
  deny from all
</Directory>

Alias /nagios/ /usr/share/nagios/
<Directory /usr/share/nagios/>
  Options None
  
  AllowOverride AuthConfig
  AuthType Basic
  AuthName "Nagios Access"
  AuthUserFile /etc/httpd/pswds
  AuthGroupFile /etc/httpd/gps
  Require group nagiosgp
  Satisfy Any
  
  order deny,allow
   deny from all
</Directory>
## end of nagios inclusion

You also need to make an addition to the directories so that Apache knows who is allowed to use it.

Access permissions section
## start of nagios inclusion
<Directory /usr/lib/nagios/cgi>
  AllowOverride AuthConfig
  AuthType Basic
  AuthName "Nagios Access"
  AuthUserFile /etc/httpd/pswds
  AuthGroupFile /etc/httpd/gps
  Require group nagiosgp
  Satisfy Any
  order allow,deny
  allow from all
  Options ExecCGI
</Directory>

<Directory /usr/share/nagios>
  AllowOverride AuthConfig
  AuthType Basic
  AuthName "Nagios Access"
  AuthUserFile /etc/httpd/pswds
  AuthGroupFile /etc/httpd/gps
  Require group nagiosgp
  Satisfy Any
  order allow,deny
  allow from all
</Directory>

## end of nagios inclusion

This might seem a bit belt-and-braces but it doesn't leave anything to chance. With the conf file updated you can restart Apache using YaST2.

Nagios

The other bit you have to configure is Nagios. This is broken down into a number of files in a sort of relational database thus...

cgi.cfg
checkcommands.cfg
command.cfg
contactgroups.cfg
contacts.cfg
dependencies.cfg
escalations.cfg
hostextinfo.cfg
hostgroups.cfg
hosts.cfg
misccommands.cfg
nagios.cfg
nrpe.cfg
nsca.cfg
original_cfgs
resource.cfg
send_nsca.cfg
services.cfg
timeperiods.cfg

The main configuration of Nagios is in nagios.cfg where the program is told where to look for the resources that it needs; each host has a place in the hosts.cfg and each host is part of a group (these can be which subnet they are on and so on) which are mentioned in hostgroups.cfg. Hosts are dependent upon the services of other hosts and so on - the whole lot linking together.

The contacts (people such as systems administrators on various shifts and so no) are members of contact groups and can be (individually) contacted according to their work times. In addition to this, it is possible to specify scheduled downtime so that people are not getting warnings about things that are not really happening.

The best way of getting to know Nagios is to set up a simple network with just a few hosts and a few services (say, just pings to start with and perhaps a http server). Configure it and then start Nagios in YaST2. If anything is wrong, the error log (config.err in /var/log/nagios) will tell you what it is (or at least the first ones it comes across until things get so confusing that it just gives up - things have to be fairly bad for this to happen though and it usually does a good job of letting you know what it wrong).

Once it is up and running, you can access it via a web browser on any machine that you have so permitted. You will have to type your userID and password and then you are in. Click on Tac tical Overview and you will be able to see at a glance if there is anything wrong with hosts or services.

If you have specified the 2D co-ordinates in the hosts.cfg file, click on the Status Map in the menu (left frame) will give you a picture like the one on the right.

On the right of the diagram, the LAN is defined and then the various routers and firewalls lead out of the local system onto the ISP's system and then to hosts on the Internet. You can configure Nagios to look at these as well so, apart from your outsources website, you can have your favourite search engines or anything you like. As long as the owners will let you ping it or check the http service (or whatever you want - as permitted), Nagios can check it. With systems owned by other people, it is a good idea to check them fairly infrequently as these will have a fair amount of demand on them any way and to have several hundred of their customers pinging it once a minute just to see if it still there will probably lead them to block you or at least complain. Once every 15 minutes, once per hour (or day even) would be more appropriate depending on yours and their circumstances.

Click on Service Detail will get you a picture like the one on the right. Each host has the services described and you can look at the status information - so, say you wanted to know how much disk space there was on a particular machine or how fast the ping was, you could find out on this page.

Click on any of the links on here and they will take you to the appropriate page (services, hosts, trends and so on).

If, in the above page, you click on a service and then "View Alert Histogram for This Service", you get an image like the one on the right. You can specify the report period (last day, month, this year and so on) and the Breakdown type (Day of the month, Day of the week, hour of the day and so on) so that you can see if anything happens at a specific time of the day, week, month and so on.

You can also state types of states to graph. Selecting hard and soft states will give you the most results. Clicking on the "Update" button will give you your new image.

If you click on "Trends For This Service", you will get a picture like this one. You can see where the service fluctuates between OK, Warning, Unknown, Critical and Indeterminate.

If you click on a portion of the bar, it will zoom in. If you want to zoom out, change the zoom factor to a negative value and click on the update button.

Again, you can change the time period and investigate any part of the record you like. If you find that things go pear-shaped with disk space and then clear themselves up every day at the same time, it might be that you have gone over a warning level with a log and at the same time each day, the log is archived and the problem clears itself up. If you want to try that out, you can set the loglevel in Squid to 5 (remember to turn it back to 1 afterwards).

If you want to see Nagios running on a site and have a play around with it, go to http://www.nagios.org/demo.php (or click on the image on the right which will open a new browser window) where instructions are given on visiting such a site.

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