Davrom Consulting Pty Ltd

Established Since 2001
PO Box 1644, Sunnybank Hills, Qld, 4109
ABN: 81 096 990 804


Site Time: 24 September 2017 - 20:22




Back to Newsletters

KEYWORDS= Davrom Consulting Newsletter - Issue # 43 - Dated: 12 Dec 2008


From the desk of David Clark

Well its Christmas time again and by now most of us are looking at spending a
few days with family and friends (and food and .....). We are available for
support over the Christmas break excluding the usual public holidays.

In this last issue for the year I have covered using the /etc/hosts file as
your network setup reference and reviewed some of the solutions we have worked
on during the past year that might help others become aware things you can do
with Linux and UNIX.

I would like to wish all of you a very Holy and Happy Christmas and that the
New Year sees you healthy, happy and prosperous.

I would like to thank the reader for their time in reading this
newsletter.

David.M.Clark


UNIX Quote


By golly, I'm beginning to think Linux really *is* the best thing since
sliced bread.
-- Vance Petree, Virginia Power


hosts file

A practice that I have followed for a long time now is to use the hosts file
to keep an accurate updated record of what IP addresses are most relevant to
the Linux/UNIX servers in the network.

As not all sites or at least most sites do not run their own internal DNS
server (Domain Name Server) to lookup names to map to IP addresses, keeping
an update hosts file is essential in maintaining a network and diagnosing any
network issues. Sites running DHCP will not require the hosts file to be too
detailed but the average server should contain as much network device
information as possible.

On Linux and UNIX the /etc/hosts file contains, at the very least, the local
loopback IP address of 127.0.0.1 (never remove or alter this entry) and the local
LAN IP address of the current server.

By adding other IP addresses on your LAN to the /etc/hosts file gives you a
central record of what devices are actually connected to your network. A
typical hosts file might be:


127.0.0.1		localhost.localdomain localhost

#
## Servers
#
192.168.22.1 brisbane.myoz.com.au brisbane # Brisbane Server
192.168.22.7 mail.myoz.com.au mail # Brisbane mail Server
192.168.22.9 windoze.myoz.com.au windoze # Brisbane Windoze Server
192.168.25.1 gcoast.myoz.com.au gcoast # Gold Coast Server

#
## PCs in network
#
192.168.22.101 pc101.myoz.com.au pc101 # John Smith PC
192.168.22.102 pc102.myoz.com.au pc102 # Mary Jane PC
192.168.22.103 pc103.myoz.com.au pc103 # Franz Van Elk PC
192.168.22.104 pc104.myoz.com.au pc104 # Mel Chavez Laptop

#
## Routers and gateways
#
192.168.22.254 sg300.myoz.com.au sg300 gateway # SnapGear SG300
192.168.22.105 wap4000.myoz.com.au wap4000 # WAP4000

#
## Printers
#
192.168.22.150 uplaser # Brisbane Upstairs Laser
192.168.25.150 hp2200 # Gold Coast HP 2200

#
##
### Eof: /etc/hosts


Note the use of the # symbol throughout the file to place comments on what the
entries pertain to. Adding the additional comment to the end of the each IP
address line is always especially helpful.

It is very simple to then see what IP addresses are available for new network
devices and gives you the ability to use utilities like ping, rcp, rsh, rcmd,
ssh, rsync and traceroute without having to remember the IP address.

One final thing I recommend with /etc/hosts once it is updated is to then
replicate it around the network to the other servers and Windows PCs. A copy
of the hosts file in Windows XP can be found in
C:\windows\system32\drivers\etc folder and is called hosts. Older Windows
versions had a hosts.sam file which you then renamed and modified to act as a
real hosts file.

Why not look at making your hosts file your central source of network
reference.


Davrom projects over the past year

It is always good to look back over a year or two and revise projects you have
been involved with and to this end I have listed here some of the projects and
kinds of capabilities existing with UNIX and Linux systems aside from being
application and basic e-mail/web servers. The following is a list of solutions
both custom written for the customer or simply implementing another phase of an
existing technology solution available.

Squirrelmail: Squirrelmail is still one of the best webmail based solutions
available. This facility allows remote users to browse to the web server and
access e-mail via web browser. This is implemented on all Davrom installed web
servers. Some customers have opted for extra plugin features to be installed to
have features like the browser not being able to remember the password
(ideal for security when using someone else's browser) included in webmail.

Remote file uploads/downloads: Using both HTML (PHP) and FTP we have been involved
in projects that allow remote users to upload and download files to/from their
company's web server. We have also designed web interfaces that allow
administrators to control access to the HTML/ftp sites.

Secure e-mail groups with Procmail: We have implemented various procmail
solutions which allow a defined group of e-mail addresses to pass e-mail to
each other without the fear of e-mail being sent to the group by spammers or
non-group members. Procmail is an extremely powerful extension to Linux/UNIX
e-mail servers and can be used to control spam or create automated
distribution e-mail lists as well as handle incoming e-mails in a whole host
of ways.

Secured websites: We have implemented a number of secure websites using PHP
technology to allow users to access websites using a username and password to
access private/company information via web browser.

Centralised backup to USB drive: With the high availablity of affordable large
USB hard drives, a lot of customers are now running solutions like our dav2usb
product that performs backups of their entire UNIX/Linux systems to external
USB hard drives. We are finding that more and more people are favouring backup
to USB drives instead of tapes owing to their pricing, capacity and ease of
restore capability.

VMware: 2008 is surely our year of VMware. We have installed quite a few
VMware based solutions these past two years with the greater portion of these
this year. VMware offers a highly flexible way to continue and preserve to use
older applications running on older operating systems that are no longer
compatible with the latest hardware architecture. The most common of these of
late is running older SCO application servers inside Linux Fedora servers or
Windows Servers. On my desktop I am running various other UNIX, Linux and one
Windows VM so I can boot these and test various things for customers - all
without needing separate hardware.

General e-mail solutions: We have continued to develop davromspam which is a
web front-end into controlling and monitoring SpamAssassin including white and
black listing capabilities.


From the Trenches
Some comic or not so comic relief from the support days gone by.

This one has been going around for some years now in one form or another.

UNIX Christmas Song:

better !pout !cry
better watchout
lpr why
santa claus town

cat /etc/passwd >list
ncheck list
ncheck list
cat list | grep naughty >nogiftlist
cat list | grep nice >giftlist
santa claus town

who | grep sleeping
who | grep awake
who | grep bad || good
for (goodness sake) {
be good
}


Tech Tip

Have you ever wanted to kill off a set of processes or print jobs that match a
specific pattern?

Here's how to cancel print jobs destined for a particular printer:

lpstat laser1 | awk '{print $1}' | xargs cancel

This will run the cancel command (thanks to xargs) on all print jobs currently
queued to the laser1 printer.

Another handy command that you can run with some caution is to bulk kill a
specific set of processes. Perhaps you are running Apache and it won't close
down - here is how to kill off all proccesses that are running for Apache:

ps -ef | grep httpd | grep -v grep | awk '{print $2}' | sort -rn | xargs kill

First our "ps -ef" gives us a listing of all process.
Then "grep" shows us the httpd processes.
We ignore our "grep" command using "grep -v grep" so it doesn't try to kill it.
awk extracts the second field from the "ps -ef" listing which is the proccess ID.
We run this through sort numerically in reverse order.
Finally xargs then runs a kill command on the process list.

You can't beat UNIX/Linux for this kind of control over the operating
environment.



Back to Newsletters




Website design by Davrom Consulting Pty Ltd
This site is fully tested with Google Chrome and Firefox web bowsers

Home Page | Support | Misc | David's Pages | Podcasts | Contact Us | Blog