Archive for the ‘Server Admin’ Category

Buy Ubuntu Training

April 24, 2009 Leave a comment

Why buy Ubuntu training? Because you might spend all afternoon trying to fix your wireless, or an entire morning fiddling with the Ubuntu terminal. As a beginner these setbacks can be extremely frustrating and obviously time consuming. This is the main reason we created a collection of Ubuntu training videos. We wanted to provide a solution that would be quick to deploy and easy for Ubuntu beginners to understand. Now you can forget spending hours waiting for responses in the forum that can be complicated to understand, just pop in the instructional Ubuntu training CD and enjoy to-the-point video clips with voice narration that walk you through common Ubuntu practices. Our Ubuntu training CD now includes over 150 training videos and has been updated for the Ubuntu 9.04 release on April 23rd, 2009. Buy It For $19.95

We’ve also added the Ubuntu Pack and Ubuntu Superpack which combine our most popular Ubuntu training videos with Ubuntu manuals and PDFs for added support.

Ubuntu 9.04: Installing Landscape on the Server

April 13, 2009 Leave a comment

Landscape Web-Based System Management
This option provides system management and monitoring. Landscape provides central management for multiple systems using a web-based interface. This interface provides easy access for updates to all of the servers/desktops you are managing as well as monitoring for users, processes, and inventory control.

Manage many machines at once
Group machines to match your needs
Manage packages across the network
Integrate custom repositories
Manage users easily
Handle security updates efficiently
Support disconnected systems


As I read these features it brought back my early years using Novell’s ZENWorks Desktop Management to roll out updates to Windows machines, push images to desktops, monitor and repair desktops. It was great stuff, though often bloated and cumbersome, but it got the job done. For busy administrators this may be an option that is worthy of consideration. Larger companies with higher skill levels and higher ratios of servers per admin will certainly take a look at this but smaller companies will shy away from the cost.
Certainly having these resources in hand can save time and will provide information that administrators should know about the systems they manage. The cost $150 per machine, per year…ouch.

Installing Landscape
During installation you have the option to set up the server to act as a landscape-client. Give it a unique “Computer Title”.

Next provide an account name for the client.


Also add a registration password.


Now you can access this server from your web based station …once you have made payment. There is a 60 day trial to see how you like it.

Set Up Secure FTP

February 2, 2009 1 comment

As popular as FTP is FTP communication is not secure, all communication is plain text and can be easily captured. Despite this serious weakness, few do anything to secure it. There are simple ways to correct this with VSFTPD.


FTPS is also known as FTPS Secure or FTP-SSL.  What FTPS does is add the Transport Layer Security (TLS) and the Secure Sockets Layer (SSL) to the normal FTP on the same port 21.  It is easy to confuse FTPS on port 21 with SFTP which is actually SSH on port 22.
Add these settings to your /etc/vsftpd.conf file and you will have an anonymous ftp server that will allow anyone to download files from /var/ftp but they cannot upload. It will also protect all of your users as they must ftp into their home accounts using ssl.

rsa_cert_file=/ etc/vsftpd.pem

You do not need to create the self-signed certificate as they are already created by the vsftpd server as you can see listed. Notice that ssl is enabled only for local logins, users who have accounts on the machine. The connection will still be on port 21. Once you have the server set up you will need a client that is ftps compatible.
Create Self-Signed Certificate
You can create a self-signed certificate with this command which will create a certificate for 1 year and the pem file is then saved in the /etc/directory. Note that you will need to change the /etc/vsftpd.conf file to enter the path of this file. You will be asked several questions which will identify your organization.
# openssl req -x509 -nodes -days 365 -newkey rsa:1024 -keyout /etc/vsftpd.pem -out /etc/vsftpd.pem
Generating a 1024 bit RSA private key
writing new private key to ‘/etc/vsftpd.pem’
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter ‘.’, the field will be left blank.
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:MT
Locality Name (eg, city) []:Trout Creek
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Example LTD
Organizational Unit Name (eg, section) []:
Common Name (eg, YOUR name) []
Email Address []

Edit /etc/vsftpd.conf and comment out the rsa certificate and private key files that are there by default and add these lines which show the path to your self-signed certificate.
Restart the ftp server.

service vsftpd restart

Using a FTP Client that is SSL/TLS Compatible

The popular Linux ftp client gFTP will not connect using SSL when you are using self-signed certificates, you would have to purchase a real certificate for your business. Another Linux alternative is to use ftp-ssl. This is a command line version of ftp and actually will replace ftp with this client. It functions that same as ftp. It will attempt to connect using ssl, if it is not enabled it will drop back to regular ftp. The Filezilla version for Linux continued to crash when the connection was made, so it is not a reliable option.
When you connect you will be asked to accept the self-signed certificate, either which you made or the default for vsftp.

Accept the certificate and you have encrypted FTP on port 21.
If you have users connecting with FileZilla for Windows, which is reliable, you will need to make these changes so they can log in with SSL. Note the port is still 21 but the Servertype is now FTP over SSL.

Categories: Server Admin

Understanding Network Address Translation, NAT

January 31, 2009 Leave a comment

Network Address Translation (NAT) is one of the basic functions of a circuit level gateway. The simple purpose of NAT is to hide the IP addresses of a private network from the outside world.

Normally, when a router forwards a packet from one segment to another, the packet is unchanged. With NAT, as a packet crosses from a trusted segment of a circuit level gateway to an untrusted segment, the packet is rewritten so that the packet’s source address as it appears on the private segment is replaced by a translated source address. The translated source address is what the outside world sees. Thus, the private address remains hidden from the outside world.

When a host on a public network transmits a packet to a host on the private network, the source host addresses the packet to the private host’s publicly translated address. The sender on the public side does not know the destination host’s true address. As the packet crosses the circuit level gateway, the gateway rewrites the packet so that the destination address is translated to the destination host’s private address.


This image illustrates the changes in source and destination addresses as packets cross a circuit level gateway performing network address translation


One to One Translation
One form of NAT establishes a one to one translation between an equal number of private and public host addresses. For example, each host address on a Class C network on the private side of a circuit level gateway is uniquely mapped to a corresponding host address on a Class C network on the public side of the gateway. If is the private network address and is the public network address, then outbound packets with a source address of can always be rewritten with a translated source address of, and inbound packets with a destination address of can be rewritten with a translated destination address of The mapping is persistent and bi-directional. Therefore, connections may be initiated from either side of the circuit level gateway unless a default deny policy is applied.

Pool of Translated Addresses
One form of NAT maps a large block of addresses from the private network to a small pool of addresses on the public segment. Multiple Class A addresses may be mapped to part of a Class C network block. If is the private segment’s network address and is the public pool of addresses, then an outbound packet with a source address of may be rewritten to have a translated source address of any host address in the pool of The NAT gateway will then create a temporary entry in its internal translation table to track the mapping. An inbound packet’s destination address cannot be translated unless a corresponding entry exists in the NAT table. If a current translation exists in the NAT table, the inbound packet’s destination address will be rewritten in accordance with the NAT table entry. The mapping is not persistent and is only temporarily bi-directional. An inbound connection may be accepted only until the NAT table entry expires.

Single Translated Addresses
The form of NAT commonly (but not exclusively) used in commercial circuit level gateways maps any number of addresses from the private network to a single address on the public segment. Given a private segment with the network address and a NAT policy that sets as the public address, all outbound packets from the private network will be rewritten to have a translated source address of To correctly map replies to the private host that initiated the connection, the source port number of the outbound packet must also be translated. The NAT gateway will then create a temporary entry in its internal translation table to track the translated source address and port number. An inbound packet’s destination address and port number cannot be translated unless a corresponding entry exists in the NAT table. If a current translation exists in the NAT table, the inbound packet’s destination address and port number will be rewritten in accordance with the NAT table entry. The mapping is not persistent and is only temporarily bi-directional. An inbound connection may be accepted only until the NAT table entry expires.

This image illustrates the changes in IP addresses and port numbers as packets cross a circuit level gateway performing network address and port translation.

nat Chains
netfilter implements network address translation in the nat table. This pre-defined table consists of three built-in chains, the PREROUTING, OUTPUT and POSTROUTING chains. Rules in the PREROUTING chain apply to inbound packets (packets arriving at the gateway from any direction). Rules in the OUTPUT chain apply to locally generated packets (packets that are generated on the gateway itself). Rules in the POSTROUTING chain apply to outbound packets (packets leaving the gateway in any direction).

nat Targets
The nat table includes the built-in targets MASQUERADE, SNAT, DNAT, NETMAP and REDIRECT.

The MASQUERADE target is available in the POSTROUTING chain. MASQUERADE is intended to be used where a firewall’s public side IP address is dynamically assigned, such as where an ISP assigns IP addresses by DHCP. MASQUERADE translates all private network addresses to the single address of the external interface as illustrated, performing port translation as needed and rewriting the destination address and port of replies as needed. When the firewall’s external IP address is released or changed, all translations are dropped.

The SNAT target is available in the POSTROUTING chain. SNAT may be used on a firewall with statically assigned IP addresses. SNAT provides outbound (more trusted to less trusted) network address translation to a pool of public side addresses such that the source address of each outbound packet is translated to an address from the pool, with port translation being performed as needed and the destination address and port of replies being rewritten as needed.

SNAT can use a single public side address as an alternative to a pool of addresses, making SNAT comparable to MASQUERADE. However, SNAT should not be used with dynamically assigned public addresses.

Conversely to SNAT, the DNAT target is available in the PREROUTING and OUTPUT chains and provides inbound (less trusted to more trusted) network address translation. When a connection is initiated from a less trusted network, the destination address is the address of the firewall interface that faces the originating network. DNAT translates the destination address to the address of a host on a more trusted segment. Optionally, the destination port may also be translated. The source address and port of replies from the more trusted segment will be rewritten as needed.

DNAT can use a pool of destination addresses and ports, providing a simple circuit level method of performing load balancing across a number of hosts such as a farm of web servers.

The NETMAP target provides static one to one translation between two network blocks of equal size.

The REDIRECT target is available in the PREROUTING and OUTPUT chains. REDIRECT translates the destination IP address of each packet arriving on any interface to the IP address of the interface on which the packet arrived. For example, REDIRECT will translate the destination address of any packet arriving at eth2. Optionally, the destination port may also be translated. Among other uses, REDIRECT facilitates use of transparent proxies whereby client software such as web browsers may be automatically redirected through the firewall to a proxy server without reconfiguration on the client side.

Wanted: A Career as a Linux Admin

January 12, 2009 1 comment

Here is a unique Linux Career Opportunity. We are currently looking for 1-3 people interested in developing into Linux Admins/Trainers. Our interest is in people we can train and develop over a 60 week course. What is unique about this course is that you will work for us while you are training. This will offset the cost of the course by as much as 50%. The course is $400 a month for the 15 months but up to $200 each month will provided by your work, writing for us. This means that you can get the course for half-price if you can keep up with the work load.
This course is put on by CyberMontana Inc. which trains as many as 75 students each week. We have a number of Linux training sites and business options.

What we are looking for:

1. Self-Motivated Individual

We are looking for someone who can get assignments done on their own. They can do research, problem solving and create documentation without needing someone’s help.

2. Ability to Write

Individuals who are interested must be willing and able to write clearly and be able to express themselves in English so that other can understand.

3. Tenacious

Problems are hard to solve at times. We need people who will aggressively pursue the problem solution until they can arrive at a solution. We are not interested in quitters.

4. Ability to Train with Patience

People are not easy to work with at times. We need trainers who will be patient and diligent despite difficulties with students.

5. Innovation

We are looking for people who have new ideas and new ways of working with technology. The Internet and Linux specifically is rapidly changing.

Outline of the Course
Stage 1: Basic Training (20 weeks)

The Basic Training Section will include 10 weeks of Server Administration and 10 weeks of LPI Certification Training. The goal of this section will be to not only test your desire to learn difficult information but provide you will the information to get LPI Certified, Linux + Certified or RHCT.

Stage 2: Disto Expert (20 week

The second 20 weeks will focus on helping you become an expert in one Linux distribution. During this time you will be required to write extensively and set up a test lab in order to focus on skills with one distribution. This will be foundational for your future as an Admin/Trainer.

Stage 3: Project Documentation (20 weeks)

You will be assigned projects to document and provide solutions. During this section you may be assigned jobs with clients or act as a trainer in specific situations. This will all be done under supervision.

The ultimate goal is to not only provide you with the training and certifications that will get you into a Linux Career but also work toward providing you with a job.

If this looks like something you are interested in please send a 500 word example of your writing skills on a Linux topic and a resume to:

mike at

This opportunity will be open to several individuals each quarter, you will have to apply to see if we have current openings.


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