An operating system is the main software component of a computer it controls all the hardware and makes everything work; there are various operating systems available each with different usages and software. The most common is Windows mainly due to their wide usage and most new computers will come with Windows pre installed. I have written a post here about Linux operating systems and I would recommend giving it a read and at least trying a Linux operating system.
I am going to take you through the steps required to start the installation process/wizards for installing an operating system. All systems are different so the content below may not be 100% accurate for your system but it should be simple enough to figure out the alternative method your system uses.
Preparation
For the first step you need to get all your resources including any installation CD keys (if required), a CD/DVD with the desired operating system or another alternative method such as a bootable memory stick.
Memory stick / USB drive
To simply this process you can download some software which will allow you to select the operating systems you wish to install onto your device, this software is great as its simple to use provider’s step by step instructions and allows multiple OS installers on one single device. The software you want is Universal USB Installer there is a version for most operating systems.
CD/DVD If you have downloaded an OS image from the internet then you need to burn the ISO or IMG file onto a disk, this can be accomplished by installing and running CD/DVD burning software such as ImgBurn available here or if you’re using Linux find some alternative software. Burning the image using ImgBurn is relatively easy insert a CD/DVD into the drive and click Write image file to disk browse to the image location and burning will begin; it may popup with some messages about making it a bootable disk click Yes or Use Recommended settings.
Booting
Now it’s time to begin the installation process first insert the CD/DVD into the drive and restart your computer the computer should now boot from the CD/DVD and begin the loading process, if you are trying to install a Windows operating system a message will appear asking you to Press any button to boot from CD you need to do exactly what it says or it will just skip booting from the CD and boot straight from the hard drive (boots to the currently installed operating system). If it fails to boot from the CD/DVD and boots straight from the hard drive we need to manually tell the computer which device to boot from this is achieved on most systems by pressing F12 during the boot up stage, as soon as the computer first starts immediately start pressing the button and you should be presented with a menu like below.
The screen you receive may differ slightly or completely but all you need to do is find the drive you want to boot from which in my case is CD-ROM so I press the “c” key. The bootable media should now beginning loading and now you ready to start installing your new operating system.
Well it’s been a long time since I have done a post or any work related to any of the projects I have been working on and they have been on hold. I am starting to begin blogging again due to me recently finished university and starting a new job as a junior software developer I basically spend all hours of the day sitting in from of a computer doing what i love and getting paid for it, who can complain :). I got my exam results back a couple of days ago and I have passed all my units giving me a HND Computing qualification, I can’t decide if I want to maybe upgrade it to a degree in web development through open university but I do know for the moment I just want work and blog.
I will be getting back to work on Bitsy.eu in the new couple of weeks Imp going on holiday soon so going to start after that, I want to finish it as at the moment there are allot of issues including being used for illegal activities as one person pointed out, they took their time to email me with a bunch of url which were being used on my service which pointed to viruses (which have now been removed), I want to adjust my service to combat this type of activity. I’ve also purchased a second domain (http://bsy.me/) which is a alias of http://bitsy.eu/ its basically just a shorter domain so that your shorten links can be even smaller for services such as twitter where every character counts.
I’m using Virtualmin which is a UI for managing web servers and such I could get rid of the UI and just configure everything myself but for usability I just use Virtualmin (I also host some clients websites so they need a easy to use interface), with my installation of Virtualmin on a CentOS 5 operating system with bleeding edge package repository enabled I’m left with the following software versions.
Apache (2.2.3)
PHP (5.2.17)
MySQL (5.0)
BIND (9.6.3)
This is an ok setup but I want to use the latest stable versions mainly for all the security fixes here is the setup which I now run it was simple to update the current packages retained all settings and data and works fine with Virtualmin.
Apache (2.2.17)
PHP (5.3.6)
MySQL (5.5.10)
BIND (9.7.3)
The only problem which I have found so far after updating was when I tried to run one of my virtual hosts using suexec (it a security feature for apache which allow you to run a virtual host as a specific user) there was an issue with the default configuration the fix was easy and only required me to recompile the suexec from source with some slight modifications to work with Virtualmin.
WARNING / MUST READ I have performed the following methods 3 times and every time everything has worked correctly and Virtualmin still operates correctly, this warnings here just to tell you I am not responsible if you do something wrong, break your system or anything of the kind.
Beginning Steps
If you are updating all 4 packages I would do it in this order MySQL, BIND, Apache and PHP this is only due to me normally doing it in this order, I have read somewhere updating PHP then apache can cause some errors but not too sure on this. I would also recommend navigating to your tmp folder.
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cd/tmp
This is so that all the files we download will automatically be deleted later by the system, now we need to download the files we need for updating from somewhere, you can compile the different versions from source but I will be using precompiled installation files. You can get these from the site below.
RPM –-nodeps and –-force During the following guide you may need to use the –-nodeps or –-force commands to complete the installation this will normally only be an issue if you already have a older version of the package installed and installing the same package but a different version, you have to make sure you use the two commands in the correct situations or you can break your system. You should always try running the RPM using the following command.
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rpm–Uhv filename.rpm
If you then receive a message similar to
You must install the required dependency as your system is missing it, this can be achieved by going to http://pkgs.org/ searching for the dependency for example apr-util-ldap and downloading the rpm required for your system, then run the rpm installation command for the new downloaded rpm.
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rpm–Uhv filename.rpm
Once the installation of all required dependencies is complete (you may try installing one dependency to then find the dependency your trying to install requires another dependency this is normal) you can then try running the rpm installation command again for the main package you wish to install, if you receive a message similar to the one below.
You will receive this message if you are updating some already installed software which is a dependency off another piece of software, in the example above openssh-server and openssh-clients needs openssh version 4.3 installed to run correctly, I received the message above because I was trying to update openssh to version 5.5. In this case I would use the following command.
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rpm–Uhv filename.rpm—nodeps
I would then have to download openssh-server version 5.5 and openssh-clients version 5.5 and also update and install any other required dependencies. The –nodeps attribute allows the installation to continue by skipping the dependency check. The –force attribute is used if the installation complains about files already existing from another package, this is caused if you are updating a package you want the new files to replace the old package so adding the –force will force the new installation replacing the old files.
Extra Checking / Package Fixing
After using this guide to update some friends server i have discovered that you can use the package-cleanup tool to find any dependency problems which you may have. By typeing the exact command below.
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package–cleanup—problems
A list of all packages which have a dependency issue will display, if for example we have installed mysql-server 5.5.10 but it is saving mysql-client requires dependency 5.0.0.1, then you have not installed the correct version of mysql-client. You can fix this issue by finding the correct RPM with the correct version you where tryihng to install so in the example we would be looking for mysql-client 5.5.10.
This is a problem I’ve ran into many times especially when I first started using CSS and divs to build websites, you may have noticed (or not) that if you have a container DIV with some child DIVs which are using the float: attribute the container doesn’t resize to fit the child DIVs, if you where to remove the float: attribute from the child DIVs the container will adjust to the size of the containers again.
Example 1
This is child 1
This is child 2
HTML Code
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<div class=“container”>
<div class=“child1”>This is child1</div>
<div class=“child2”>This is child2</div>
</div>
CSS Code
CSS
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.container {
border:thicksolid#000;
width:200px;
}
.child1 {
width:100px;
background-color:#0C0;
}
.child2 {
width:100px;
background-color:#C30;
}
From this example above you can see what a container DIV looks like when the child DIVs do not contain the float: attribute, the container DIV resizes and adjusts depending on the size of the child DIVs, but without the float attribute are two child DIVs do not fit side by side.
Example 2
This is child 1
This is child 2
HTML Code
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<div class=“container”>
<div class=“child1”>This is child1</div>
<div class=“child2”>This is child2</div>
</div>
CSS Code
CSS
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.container {
border:thicksolid#000;
width:200px;
}
.child1 {
width:100px;
background-color:#0C0;
float:left;
}
.child2 {
width:100px;
background-color:#C30;
float:left;
}
Now we are using the exact same code above the only difference is the float: attribute is now being used which allows the two child DIVs to sit next to each other, but now are container has stopped resizing and shows as if there is no data present. There is a simple and effective fix using CSS which will allow the container to resize exactly how it does in example 1 but still allow the two child DIVs to use the float: attribute, below is the CSS code which fixes this problem.
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.clearfix:after
{
content:“.”;
display:block;
height:0;
clear:both;
visibility:hidden;
}
Using this CSS code is very simple, all you have to do is simply rename .clearfix (making sure to leave :after as this will make the CSS apply after loading all the elements, if it is applied before it will load incorrectly and may not work) with the name of the class used for your container DIV (if you have used id instead you need to replace the . with a #), this CSS code can be used in a variety of ways but this is the simplest, I have provided an example below demonstrating it working using the code from example 2.
SSH is a secure shell command line technology allowing a user to connect to a second computer and perform many tasks securely. I have written a post which is found here which tells out all about the SSH technology. In this post I am showing you how to connect to a SSH server in Windows and Linux operating systems using public and private key authentication, you can find my password authentication guide here. I am assuming you have already created the public and private key files and the SSH server you are attempting to connect to is setup to use key authentication.
SSH using windows To allow us to perform SSH communications we need to download a SSH client which allows us to transmit and understand responses, the software we are going to be using is called PuTTy which can be found here, a direct link to the download required is here. Please download the file to an easy to find location such as the desktop. You will also need to download a program called PuTTyGen which is found here. If the key was generated on a Linux system then the private key you will be using will need to be converted from an OpenSSH format to format putty can understand, this is achieved using PuTTyGen. If you are not sure if your private key has already been converted then just continue with the converting stage anyways it won’t hurt your key in anyway.
Once both the applications have downloaded you simply double click PuTTyGen and it will launch, there is no need for any installation of this program. Your first step is to load the private key which is done by clicking File located at the top of the application and selecting Load Private Key.
You will then be presented with a window like below, you have to browse to your private key and select it, then click load.
Now the key is loaded into PuTTy gen and you will see a window which looks just like the one bellow, if you have a password set on the private key you may receive a password popup and need to provide a valid password before the software can load the key.
All we have to do now is save the private key in the format PuTTy will understand which is achieved by clicking on the Save private key button, you will then have to select the location to save your key. If you are not using a password with your key then PuTTyGen will warn you about not using a password just click yes.
Conversion of your key is now complete and you can close the PuTTyGen application and start the PuTTy software. You will begin with a screen which looks like this it may be slightly different if you have used PuTTy before.
There are two fields on this page which we are interested in and that is the textboxes located at the top of the application labelled “Host name (or IP address” and “Port”, we need to provide the IP address (can also provide a hostname if it resolves to the correct IP address) and the port number which the remote SSH server (located on the second computer) is running on by default this is 22 but can be changed.
As you can see from the image above I have provided the IP address of the second computer and a port number of 22, the computer I am connecting to has a IP address of 10.0.2.15 and the SSH server is listening on port 22 for connections. Please enter the IP address or hostname of your second computer and the port number (most probably 22).
We now need to tell putty where are private key file is located so that when the SSH server ask PuTTy knows which key to send. On the left side of the application there is a group of categories, you need to click the plus item located next to SSH and then on Auth. Your screen should now look like above.
Now click on the Browse button and locate the private key file. You must make sure you select your converted version or PuTTy won’t show the file in the file browser.
All we have to do now is click on the Open button and the connection will begin.
You may receive an error message like the one above, this means it failed to gain a connection to the second computer and there are many causes of this error. First thing would to make sure the SSH server is running on the second computer and the port is allowed on the firewall, next step would be to check that you have entered the correct IP address or hostname and port number and retry.
On a successful connection to the second computer through SSH you will receive an alert similar to the one above. This key is a way to identify that the second computer is who it says it is, you don’t really have to pay any attention to this and so I normally just click the yes or no option. If you click Yes this key will be saved for further usage stopping this alert from appearing every time you try to connect to this computer, clicking No will allow you to connect but will not save for further usage meaning it will appear again on the next login and cancel will stop the connection to the second machine. Now we are beginning the login progress where we need to enter the username of the user we want to login and then the password for that user. Simply type the username and press the enter key.
SSH using Linux Unlike windows operating systems Linux has the ability to communicate with a SSH server straight after installation of the operating system (no third party software is required). I am going to be using Ubuntu operating system but this will work on all distributions of Linux. First we need to launch the terminal which is a command line interface which will allow us to perform the SSH login. On Ubuntu this can be found by going to Applications then accessories. You will be presented with a black window with some white text.
Before we do anything with the terminal we need to place are private key into the correct directory, the private key needs to be placed into ~/.ssh/ and needs to be called id_dsa or id_rsa. You can either use the desktop to move this file to the location (you will need to enable hidden folders) or the terminal which is achieved by typing this command. You will have to replace /home/Shane/Desktop/id_dsa with the location of your private key.
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Cp/home/Shane/Desktop/id_dsa~/.ssh/
Now that we have the file in the correct place all we now have to do is simply type ssh-add and you will receive a reply similar to the one below. Now all we have to do is begin the SSH connection.
To start an SSH connection we have to type a command to begin the SSH software, we also have to specify the port which the SSH server we are trying to connect to is listening on (normally 22), we also have to specify the IP address or hostname and the user we wish to login with (if not user is specified it will try to login with the user we are logged in with on are client), the command to do this looks like this.
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ssh–p22root@192.168.0.12
What this command will do is start a SSH connection to the SSH server running on the computer using the IP address 192.168.0.12 and listening on port 22, it will attempt to login with the user root. We can change the port we are connecting to by changing –p 22 to –p 2290, the SSH server must be listening on the port for it to be successful. We specify the user we want to login by placing the username then an @ symbol before the IP or hostname of the computer we wish to connect to.
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ssh–p2290bob@192.168.0.12
The command above is another example where we are connecting to the computer which is used IP address 192.168.0.12 with the user bob. The SSH server is listening on 2290 instead of 22 so we specify the port number. If you are connecting to a SSH server which is using the default port (22) then you do not need to provide the –p argument, you can use the following command and it will automatically try connecting to port 22.
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ssh bob@192.168.0.12
On connection you may be presented with a message like this and you are asked if you want to continue connecting. This is normal and allows you to determine if you are connecting to the correct computer or if someone is tricking you into connecting to them so they can intercept your data, every SSH server has a RSA key which you should write down on installation of the SSH server. You can then compare this key to the key which you are being shown on the SSH client, if they match you are connecting to the correct computer, if not then it’s possible someone has tricked you into connecting to them allowing them to view any data you transmit. You should enter yes if you are sure you are connecting to the correct computer, if you enter no it will cancel all communication.
On entering yes the RSA key will be saved permanently on your computer stopping this message appearing the next time you connect using SSH to this computer. If the key changes at all another message will appear alerting you to a key change, if you haven’t reinstalled the SSH server then the key shouldn’t have changed meaning there’s a high possibility someone has tricked your SSH client into connecting to them instead of your desired computer. You should halt all communication in the event of this message unless you are sure it is safe.
If your key doesn’t require a password it will login in now, but if it does require a password you will be asked to enter the valid password, when you type your password nothing will appear but it is typing, this is a secure feature so that people can’t see how many characters are in your password.
SSH allows communicate to be achieved between two computers (usually used to control a remote computer), there are two parts to a SSH connect and that is a SSH server located on the machine we wish to connect to and a SSH client which allows us to connect to the SSH server. We need authentication methods on a SSH server to stop unwanted users remotely logging in, SSH is normally used to connect to a remote computer through the internet and so we need to apply restrictions to stop anyone from just connecting and performing changes. To stop unauthorised access we create user accounts on the remote computer, when we first start a connection we are asked to provide the username we want to login with and then the password or a private key (depending on the authentication method used by the SSH server) corresponding to the selected user.
In this post I am going to explain the differences between password and private key authentication and why you should use private key authentication. I have written a previous post about SSH which can be found here.
Password Authentication Password authentication is the process of logging in using a password which is associated with the selected user account, this is the easiest login method mainly due to passwords being used throughout the internet (online banking, shopping, eBay …..), this is also the default setting for a SSH server when first installed. It may seem secure but it does have its risks, to have a secure password it needs to consist of numbers, letters, capitals and symbols all in a random sequence making it incredibly hard to guess, but a password like this most probably isn’t easy to remember so will be written down somewhere (sticky note, notebook …) this is a security risk, even if the password isn’t written down there’s always the risk of a bruit force attack which will effectually if left long enough guess your password and once someone knows your password they can gain access immediately. Public key and private key authentication remove this issue and should always be used for that added security.
Good
Passwords can be easy to remember
Any user can login easily using a password
Bad
Subject to bruit force attacks
Passwords are easy to steal if written down
If password is known instant access can be achieved
Easy passwords can be guessed easy
A compromised account could compromise the whole system
Any computer can login with just the password
Public and Private Key Authentication
Key authentication works slightly different to password authentication you provide the username you wish to login with, then instead of a password the SSH server presents you with a public key, your SSH client then replies with the private key which corresponds with the public key and the server allows or disallows the login depending if the key was correct. No one can pass this stage without the correct private key which should be kept save and only issued to people who need to login using SSH, no login can be achieved without a matching key set stopping all bruit force password attempts. That is the 1st hurdle and a second one can be setup making it even harder to login, during the public and private key creation a password can be provided, this password encrypts the private key making it impossible to decrypt without the password. This type of private key is used in the exact same manner as a none pass worded key except when your SSH client goes to send the private key response it will ask for the password, without this password the key will not be decrypted and the SSH server will reject the login. This creates two hurdles which need to be passed to successfully login being the correct private key needs to be provided and if a password was setup then the password also needs to be provided. The whole world can know the password but without the private key no login can be achieved.
Good
The matching private key must be provided during login.
Only 1 private key is valid (can’t be faked).
Private key can be encrypted adding password authentication as a second defence
Each user account has a separate public and private key set.
The correct keys must be provided for the different users (can’t use 1 private key to login into all users).
Stops bruit force password attempts.
If password is known no login can be achieved without the private key if key was encrypted.
Bad
Can be harder for some users to setup the private key with their SSH client.
