Category: The Void

Bash: Suppressing script output

Recently I have been creating a bunch of bash scripts to automate some processes, I normally run these scripts manually so output is helpful but today I was working on a script which runs via a cronjob every 12 hours, the issue with this is that if a script outputs any data whilst being executed via cron the output is emailed to the user which ran it. This was causing an email to be sent to my inbox every 12 hours which I didn’t want (yes it allows me to verify it has run but I didn’t need to know this or want an email every 12 hours).

The answer is simple all I had to do was redirect the stdout output to a file or null location. This is achieved using the following command.

Shell

scriptname >/dev/null

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scriptname >/dev/null

What this does is send any output which was going to stdout to /dev/null so we no longer see the output. This however doesn’t hide error messages (stderror) either of the following two commands will redirect error messages.

Shell

scriptname >/dev/null 2>&1 scriptname >/dev/null 2>/dev/null

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2

scriptname >/dev/null 2>&1
scriptname >/dev/null 2>/dev/null

You can replace /dev/null with an actual file such as /home/shane/run_log.log and now output will be redirected to that file, the first line above directs both messages (stdout) and error messages (stderror) to the same location /dev/null, the second command however can be used to direct messages and error messages to separate locations / files.

Shell

scriptname >/dev/null 2>/home/shane/run_error.log

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scriptname >/dev/null 2>/home/shane/run_error.log

The following line will suppress normal message output but error output will be stored into run_error.log. Because we are writing to a file and not the shell output we no longer receive the output in an email.

5th November 2011
PHP: Dynamic Variables

Today a came across a situation where I needed to loop through some data and open up a http request using a socket connection, each loop had to open a new connection and the handler had to be stored into a new variable so that each connection could be read separately (opening a new connection using the same variable name would close the previous connection and create a new one).

It’s quite simple if you know exactly how many connections you need to open each time as you can just define the max required variables, but what if one day it needs to open 2 connections then the next it needs 8 but there is no defined maximum either (no one wants to write out 100 variables just encase and it doesn’t meet any of the coding standards either).

A dynamic variable is what we need and PHP has this built in, which has been a life saver as we can declare many unique variables but only as many as we need. Here are some examples; the first creates 10 dynamic variables (dynamic_variable_0, dynamic_variable_1, ……., dynamic_variable_9).

PHP

<?php for($a=0; $a < 10; $a++){ ${“dynamic_variable_” . $a} = $a; } ?>

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<?php
for($a=0; $a < 10; $a++){
${“dynamic_variable_” . $a} = $a;
}
?>

The following code below outputs the data from the 10 dynamic variables we created in the coding example above.

PHP

<?php for($b=0; $b < 10; $b++){ echo ${“dynamic_variable_” . $a}; } ?>

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<?php
for($b=0; $b < 10; $b++){
echo ${“dynamic_variable_” . $a};
}
?>

1st November 2011

PHP: fsockopen() – Sending POST data with HTTP request

I have come across many occurrences where I have needed to pass data to a websites form via POST, this is simple enough if doing via a browser as all you need to do is duplicate / copy the original form parse it with your default data possibly from a database and a bit of JavaScript code to initiate the form sending process. But what if you want to make it fully automatic via a cronjob? The code I am going to show you simply sends a POST request to the target web server and waits for the response. I have previously used this code to secretly post data to a website process the result and display the output in a different format (so it’s all hidden and the users on the website never know or see the other website). I have written a previous post found here related to the fsockopen function.

The Header String

This is the first bit of data we send to the web server it basically tells the web server the format of our information and any other related data, if we don’t send this the server might refuse the request or return something complexly different. I will go into this section in more detail now.

//This tells the web server what version of HTTP protocal we are using
//It also tells it the file we are sending the request to which in this case is /files/post.php which translates to shanerutter.co.uk/files/post.php
$http  = “POST /files/post.php HTTP/1.1\r\n”;

//This is the url or IP of whcih the request is coming from
$http .= “Host: shanerutter.co.uk\r\n”;

//The user agent being used to send the request
$http .= “User-Agent: ” . $_SERVER[‘HTTP_USER_AGENT’] . “\r\n”;

//The content type, this is important and much look like the following if sending POST data.
//If this is not provided the server may not process the POST data
$http .= “Content-Type: application/x-www-form-urlencoded\r\n”;

//Lets the web server know the total length/size of are POST content
//It is not always required but some servers will refuse requests if not provided
$http .= “Content-length: ” . strlen($post_data) . “\r\n”;

//Tells the server are header request is complete and the rest if content / POST data
$http .= “Connection: close\r\n\r\n”;

//Adds are post data
$http .= $post_data . “\r\n\r\n”;

//This tells the web server what version of HTTP protocal we are using

//It also tells it the file we are sending the request to which in this case is /files/post.php which translates to shanerutter.co.uk/files/post.php

$http = “POST /files/post.php HTTP/1.1\r\n”;

//This is the url or IP of whcih the request is coming from

$http .= “Host: shanerutter.co.uk\r\n”;

//The user agent being used to send the request

$http .= “User-Agent: “ . $_SERVER[‘HTTP_USER_AGENT’] . “\r\n”;

//The content type, this is important and much look like the following if sending POST data.

//If this is not provided the server may not process the POST data

$http .= “Content-Type: application/x-www-form-urlencoded\r\n”;

//Lets the web server know the total length/size of are POST content

//It is not always required but some servers will refuse requests if not provided

$http .= “Content-length: “ . strlen($post_data) . “\r\n”;

//Tells the server are header request is complete and the rest if content / POST data

$http .= “Connection: close\r\n\r\n”;

//Adds are post data

$http .= $post_data . “\r\n\r\n”;

The Code

< ?php
//Variable storing the post data we want to send. Starts with the post field name then its content followed by a & if there is another to come after it.
$post_data = ‘name=bob&age=12&county=uk’;

//Initiates a connection to example.com using port 80 with a timeout of 15 seconds.
$socket = fsockopen(“example.com”, 80, $errno, $errstr, 15);

//Checks if the connection was fine
if(!$socket){
	//Connection failed so we display the error number and message and stop the script from continuing
	echo ‘ error: ‘ . $errno . ‘ ‘ . $errstr;
	die;
}else{
	//Builds the header data we will send along with are post data. This header data tells the web server we are connecting to what 
	//we are, what we are requesting and the content type so that it can process are request.
	$http  = “POST /files/post.php HTTP/1.1\r\n”;
	$http .= “Host: shanerutter.co.uk\r\n”;
	$http .= “User-Agent: ” . $_SERVER[‘HTTP_USER_AGENT’] . “\r\n”;
	$http .= “Content-Type: application/x-www-form-urlencoded\r\n”;
	$http .= “Content-length: ” . strlen($post_data) . “\r\n”;
	$http .= “Connection: close\r\n\r\n”;
	$http .= $post_data . “\r\n\r\n”;
	//Sends are header data to the web server
	fwrite($socket, $http);		
	$contents = “”;
	//Waits for the web server to send the full response. On every line returned we append it onto the $contents 
	//variable which will store the whole returned request once completed.
	while (!feof($socket)) {
		$contents .= fgets($socket, 4096);
	}
	//Close are request or the connection will stay open untill are script has completed.
	fclose($socket);
}
?>

< ?php

//Variable storing the post data we want to send. Starts with the post field name then its content followed by a & if there is another to come after it.

$post_data = ‘name=bob&age=12&county=uk’;

//Initiates a connection to example.com using port 80 with a timeout of 15 seconds.

$socket = fsockopen(“example.com”, 80, $errno, $errstr, 15);

//Checks if the connection was fine

if(!$socket){

//Connection failed so we display the error number and message and stop the script from continuing

echo ‘ error: ‘ . $errno . ‘ ‘ . $errstr;

die;

}else{

//Builds the header data we will send along with are post data. This header data tells the web server we are connecting to what

//we are, what we are requesting and the content type so that it can process are request.

$http = “POST /files/post.php HTTP/1.1\r\n”;

$http .= “Host: shanerutter.co.uk\r\n”;

$http .= “User-Agent: “ . $_SERVER[‘HTTP_USER_AGENT’] . “\r\n”;

$http .= “Content-Type: application/x-www-form-urlencoded\r\n”;

$http .= “Content-length: “ . strlen($post_data) . “\r\n”;

$http .= “Connection: close\r\n\r\n”;

$http .= $post_data . “\r\n\r\n”;

//Sends are header data to the web server

fwrite($socket, $http);

$contents = “”;

//Waits for the web server to send the full response. On every line returned we append it onto the $contents

//variable which will store the whole returned request once completed.

while (!feof($socket)) {

$contents .= fgets($socket, 4096);

}

//Close are request or the connection will stay open untill are script has completed.

fclose($socket);

}

30th October 2011

PHP: fsockopen()

PHP has built in functions allowing your scripts to communicate with various other applications and services via a socket connection, this opens new and exciting possibilities for us PHP programmers. You might be asking yourself why? With this ability we can query mail servers, get website content whilst also providing POST and GET data, query a DNS server these socket connections are almost unlimited you can connect to virtually any host or port number and use various transport technologies such as TCP, UDP, HTTP, HTTPS, SSL, TLS this allows for a wide range or usages, it wouldn’t surprise me if you could connect to a FTP or SSH server but I have never tried this.

The main uses and real live implementations I have used with this technology were to query a web server whilst providing some POST data and retrieving the response for processing. I have also managed to get a script working which allows you to run multiple occurrences of the same script using your web servers built in multithreading technology (but each thread/occurrence of your script will process a different section of data speeding up long processes) but I will go into this in another post shortly.

PHP Manual: fsockopen

Here is an example section of code which will connect to 127.0.0.1 using port 13, the communication will be performed using UDP packets (we know this due to the udp:// at the beginning of the host address, if this is not set it defaults to HTTP). Any error numbers or messages are stored into the 2 optional variables $errno and $errstr which can be used later in are scripts to determine what to do.

<?php
$fp = fsockopen(“udp://127.0.0.1”, 13, $errno, $errstr);
if (!$fp) {
    echo “ERROR: $errno – $errstr<br />\n”;
} else {
    fwrite($fp, “\n”);
    echo fread($fp, 26);
    fclose($fp);
}
?>

<?php

$fp = fsockopen(“udp://127.0.0.1”, 13, $errno, $errstr);

if (!$fp) {

echo “ERROR: $errno – $errstr<br />\n”;

} else {

fwrite($fp, “\n”);

echo fread($fp, 26);

fclose($fp);

}

Basically the following script queries the date/time service on your own computer or server for the time then displays the response. The following is ok if you know you will get an instant response, but if we are communicating with other services such as a website where multiple lines of data are returned we need to use the following code to get the full output.

while (!feof($fp)) {
     echo fgets($fp, 128);
}

while (!feof($fp)) {

echo fgets($fp, 128);

}

What this does is loops through the complete response and each time displays the next line, until the response has been looped through completely. If you don’t need to wait for the response and only need to initiate the communication then you can remove the while loops and fread commands. This will cause your script to start the communication and then it will just continue with the rest of the script, for example I want to load a website page 20 times which takes 10 seconds each to complete. That would give my script a running time of more than 200 seconds if it was to wait for each response. Now I remove the while and fread commands and now my script only takes 2 seconds to run but still initiates the other website pages (it completes faster due to not waiting for the response from each page, but the web server which handles these websites still finishes processing the request which my script made even through nothing will ever process the response).

30th October 2011

PHP: Common configuration changes

PHP works straight out of the box with a default configuration setup specified by the PHP group which is quite restrictive; it is common for developers and server administrators to adjust the PHP settings to enable PHP applications to run smoothly or successfully. The PHP configuration settings are in a file called php.ini, the location of this file differs from each web server setup and operating system. To find out you can create a php file with the following code to view all the details about the PHP installation.

<?php
    phpinfo();
?>

<?php

phpinfo();

The loaded php.ini file can be found by looking through the data which is outputted from above PHP function, you are looking for the following two fields (Configuration File Path and Loaded Configuration File) usually located near the top of the list. If the loaded configuration file is none then PHP was unable to find a configuration file and so has reverted to the default PHP settings, to adjust the settings we need to create a php.ini in the location it is looking PHP comes with two standard php.ini files one for development and the other for production, all we need to do is rename the file we want to use to php.ini and then adjust the required settings.

Here is a link to the official PHP website manual for this file http://php.net/manual/en/ini.core.php this is a massive list of all the possible settings and there default value. Normally a setting not specified will revert to the default.

Important Information
Shared hosts have limits in place and my not allow you to directly modify the PHP configuration this depends entirely on the host and different server setups may or may not allow you to modify this file. If it is not possible to adjust the PHP configuration directly there are alternatives such as htaccess files and PHP built in method. I have written this post to tell you how to adjust your settings using alternative methods and why your hosts won’t allow you modify this file directly.

Common Changes
Your most common changes will be related to the execution times and script resource usage which if not changed cause allot of scripts which either allow uploading, image handling or large execution times to end prematurely. This is my recommendation of common changes and if you believe I have missed anything please post a comment.

Setting	What it does
max_execution_time	This is the maximum amount of time a PHP script can run before automaticly being killed and recieveing a timeout error message. The default is 30 seconds which is suitable for most websites but it is quite common for a script to need to run longer due to file uploading.
memory_limit	This is how much memory a individual PHP script can use at once, normally the default setting is adequate but if you are handling images, file uploads and large amounts of data (database or files) this setting will need adjusted. PHP will give you a error message tell you that the memory usage it to high.
post_max_size	This is the maximum size which PHP will allow for post data, normally this setting is ok by default but if you are uploading files or sending large amounts of data via POST you may need to increase this setting. Remember this is the total post size not individual post elements, meaning if you upload a 8MB file and a large string content which is 1MB the total post will be 9MB.
upload_max_filesize	As well as having the max post setting above there is also a limit on the max file size which can be uploaded via PHP, this setting is per file so if your script uploads multiple files you should be ok as long as each file is below this limit. You must remember to adjust the other settings above to be able to successfully upload large files or compensate for slow internet connections (which will require your script to wait longer for successfully upload).
max_input_time	This is the maximum time a PHP script will spend processing data received via POST and will need adjusting if large amounts of data is being transferred.
sendmail_path	This is the default PHP setting for Linux servers it specifies the mail path used by PHPs mail() function. This will only work under Linux and must be commented and the two settings below used for Windows.
SMTP	This is used to tell PHPs mail() function which SMTP server to use to send emails, this is only required on Windows servers and the setting above should be used for Linux servers. Due to PHP lacking the ability to use authentication you need to specify a SMTP server which will allow usage without authentication, most good SMTP servers have the ability to allow unauthorised connections internally.
sendmail_from	This is the from email address which will be used when sending an email via PHPs mail() function, this setting is only required to be set on Windows servers and will cause errors if not set.

6th August 2011

PHP configuration/setting changes via .htaccess and PHP

PHP has various configurable options to enable, disable or limit specific features. Most of the PHP related problems a web developer comes into is due to these limits especially if developing for multiple servers as each server will be configured differently. This is a common problem with shared hosts as you do not have the ability to adjust the PHP configuration directly leaving the developer having to adjust their code to work around the server’s limits or abandoning their host.

PHP.INI
This is the main file in which all the PHP settings are stored, on a shared host you will normally not have access to this file and so alternative methods are required to overcome limits.

Why can’t I change settings on a shared host?
As the name implies it is a shared host meaning it’s not only your website hosted on that server, by adjusting the PHP settings you could accidently break another person’s website by disabling a module they require or increasing/decreasing a limit they rely on. This would be the main reason shared host providers will not allow you to adjust the PHP settings, the other is security most hosts don’t want to allow a PHP script to run for 60 seconds or more due to server resources such as CPU, memory and internet usage, if the PHP configuration was set to loosely someone could easily modify one of their PHP scripts to crash the web server via an infinity loop.

Work Around?
There is various workarounds to overcome these limits the easiest would be if you had access to the php.ini file or managed the server yourself. Some hosts provide features where each of their clients gets a separate php.ini file, this allows the client to customer the PHP settings to their liking and the changes only affect their own websites (some limits may still be in place such as maximum execution time if your settings are too high a global setting will takes its place to stop malicious usage).

.htaccess (Apache) workaround
If you don’t know what .htaccess file is then please read this post.

This is a simple method but will not work on all hosts due to restrictions (PHP also has to be installed as a Apache module), for this to work your host needs to give you specific apache privileges which are.

AllowOverride Options

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AllowOverride Options

or

AllowOverride All

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AllowOverride All

You may be able to add either of the following lines to your .htaccess file to manually give yourself the privileges required. The next step is to add the lines of code which will change the PHP settings. The following line is the command we will be using to override the PHP setting.

php_value name value

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php_value name value

The section called name is the option you wish to change and value is the value you want to change it to, if you are wanting to adjust a setting which has a value of either 0, 1, yes, no then you must use the following line instead.

php_flag name on|off

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php_flag name on|off

A list of available commands can be found here.

http://www.php.net/manual/en/ini.list.php

In the table there is a column called “Changeable” if the value of this column for the setting you wish to change is not either “PHP_INI_ALL” or “PHP_INI_PERDIR” then you will not be able to adjust the setting using this method. Here is an example of my .htaccess file which will increase my max upload file size.

<IfModule mod_php5.c> php_value upload_max_filesize “100M” </IfModule>

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<IfModule mod_php5.c>
php_value upload_max_filesize “100M”
</IfModule>

The following will adjust my upload_max_filesize limit to 100M instead of the default value which is 2M, my options are surrounded by a IF statement which basically checks if PHP5 is in use if so then it runs the command to adjust the settings.

PHP workaround
PHP comes with the ability to override some of its predefined settings but just like the other over rights it depends entirely on the setup of the web server and may not work. The overrides for PHP work exactly the same as the .htaccess ones explained above but we use the following command to adjust the settings.

ini_set (name, value);

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ini_set (name, value);

The documentation for this function can be found here, it is used just like any normal line of PHP code here is an example of some PHP code where I have increased the file upload limit to 100M.

PHP

<?php ini_set(“upload_max_filesize”, “100M”); ?>

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<?php
ini_set(“upload_max_filesize”, “100M”);
?>

A list of all PHP settings is available here but only the settings which have PHP_INI_ALL, PHP_INI_PERDIR or PHP_INI_USER can be changed via the ini_set command.

Extra Links

http://www.php.net/manual/en/ini.list.php

4th August 2011
Apache .htaccess file

We have all visited a website as your currently viewing my blog which is a website, when you visit a website you download the files and data required for your web browser to display the desired page. The computer or server which you download a website from will be running some form of web server which is an application used to distribute the required files and code to a web browser requesting them. There is a range of web servers available but in this post I will be talking about the Apache web server and its .htaccess file.

A web server has a range of configurable options but due to every website being different you need a way to specify an option for one but not the other this is where the .htaccess file comes in. It allows you to configure options which will affect only the site it is run from, this file can be used for a range of settings such as configuring apache options (not all options are changeable due to security risks) to setting up redirects and passworded directories.

The .htaccess can be located in the main directory or any sub directory if it is placed in the main directory the settings in this file will normally apply to all files and subdirectories, where as placing it in a folder will normally only apply to that folder and its subdirectories.

Creating the .htaccess file

Creating this file on a Linux operating system is simple and the normal file creation and naming method is suitable, on windows this is a different story as Windows operating systems do not allow you to specify .htaccess as a valid file name, when you create a file on windows you normally have the name of the file and then the file exstension like below.

PHP

File.txt

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File.txt

As we need to call are file .htaccess without an extension Windows throws a wobbly and so we have to call the file htaccess and then use the following command prompt to rename the file to .htaccess.

PHP

Rename [TARGET] [NEW NAME]

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Rename [TARGET] [NEW NAME]

So here is an example of me renaming my file which is located on my desktop.

PHP

Rename C:\Users\Shane\Desktop\htaccess C:\Users\Shane\Desktop\.htaccess

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Rename C:\Users\Shane\Desktop\htaccess C:\Users\Shane\Desktop\.htaccess

Ultimate .htaccess Guide

The people at Who Is Hosting This, have created a very good guide suitable for beginners to experts. Take a look.

http://www.whoishostingthis.com/resources/htaccess/

Other commands

You can find all my other posts related to .htaccess and how you can perform specific tasks by viewing my other blog posts which can be found here.

http://shanerutter.co.uk/category/servers/apache/htaccess/

31st July 2011
Passworded – The beginning

A couple of weeks ago my brother who is very big on computer security asked me if I was able to create him a password generating script, I replied with there are loads already available to which he replies I don’t trust them. As i had some spare time I quickly put together a password generating script and placed it live on my web server, it can be viewed at http://passworded.co.uk/. It’s not the prettiest of websites as it was an quick hour job, it does work but I am planning on creating a better template / theme and adding more features such as the ability to log your generated passwords onto a user account and maybe the ability to add custom passwords (basically a password vault).

This project will slowly be developed I’m not going to be putting much effort into it at the moment but whenever I get some free time it will be spent here.

23rd July 2011
Windows SSH & SFTP Server

Recently I have been setting up various Windows server operating systems but have always had the same issue which is how to communicate / manage that server remotely, windows servers by default are managed via the RDC (remote desktop connection) but I want the ability to log into cmd (command prompt), transfer data and port forwarding. FTP isn’t an option due to data being transferred in plain text meaning anyone with the correct knowledge can view everything I’m transferring, this is why I need a secure FTP connection which just happens to be called SFTP, but to do this the remote server I’m connecting to needs a SSH server which windows doesn’t come with or natively support (unlike Linux operating systems which are fully controlled via SSH making life much easier). Below are 4 posts I have already written about SSH and how to use SSH.

What is SSH (secure shell)?

SSH Password v Public/Private Key Authentication

Creating an SSH connection using password authentication

Creating an SSH connection using public/private authentication

Thanks to software developers SSH technology can now be installed on a Windows operating system giving you the full benefits of a SSH server including the ability to access cmd remotely, use SFTP for a secure data transfer and also give you the ability to port forward which we will not be getting into in this post.

There are various software choices available but I have chosen to use freeSSHd as I found it very easy to setup which took about 5 minutes. The installation process is like any other application and all you need to do if follow the installation steps, at the end of installation you will be prompted to create private keys I would recommend click Yes, and then you will be prompted if you want to install freeSSHd as a windows service, this option is entirely up to you but as I want my SSH server to always run and be hidden whilst running I installed it as a windows service.

Server Starting, Stopping and Restarting
The server is managed via a graphical interface it can be managed via command line as this was the normal method until one of the latest updates added the graphic interface. When you first run the application you will see a screen like this.

If you are running the server as a service it will say the SSH server is not running and this is normal, if you’re not running it as a service and receiving this screen then your SSH server isn’t running. The main difference between running it as a service and a normal program is that the graphic interface has to be running for the server to run if not installed as a service, starting, stopping of the server is also done through the graphical interface.

If you’re running as a service then you use the graphical interface to adjust settings but you start, stop and restart the actual SSH server service by going into the Windows Services directory (to apply any new settings changes you must restart the SSH server) which if found by going to.

Control Panel -> Administrative Tools -> Services

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Control Panel –> Administrative Tools –> Services

Find the service in the list it should be called FreeSSHDService and then right click it to see a list of options, remember that when you make a modification to the SSH server settings using the graphical interface you must stop and start the SSH server for the changes to take effect.

Basic Configuration

Now we need to do some basic configuration such as setting up account login and home directory, once these have been set the default options for the rest of the settings are suitable for a basic setup, there is some which I would recommend changing but I will talk about them after we setup the login and home directory.

First we need to go to the SFTP tab; this is where we set the home directory which is the directory you will see when you login through SFTP. Due to only being able to set one directory for all SFTP logins I came across a problem when I wanted to share multiple folders and drives, please read further down where I will explain how I managed to share multiple folders and drives.

Now that the SFTP directory has been set all we need to do is create the actual user or users we want to login with, this is done by going to the Users tab.

A list of all the current users will be shown by default but as I have just installed the software there is currently no users, this is also where you can modify and remove users as well as add which I am going to do now.

The user creation process is simple you simply click the Add button and the following window above will show, you then simply enter the desired username into the Login text field and select the authorization method from the drop down box, there are 3 options.

NT authentication
Uses the current Windows account already created on the system for authentication, you simply just have to specify the user’s username in the Login text field and it will use the Windows password during login.

Password stored as SHA1 hash
If you don’t want to use the Windows account for login then you can provide a username and password by choosing this option, this is the option I have chosen as I don’t want to create separate Windows logins for each user who needs SSH access.

Public Key (SSH only)
Public keys is another login method which is probably the most secure, here is a blog post I have already written about public and private key authentication. SSH Password v Public/Private Key Authentication.

Now that we have selected a username, password and authentication method all we need to do is specify what access rights the user has, Shell is the ability to login using a SSH client like PuTTy to gain access to command prompt. SFTP is the same as FTP but secure/encrypted and tunnelling is the ability to forward port traffic from the computer the SSH client is on to the SSH server (this is also known as port forwarding and should only be allowed for trusted users).

Advanced Features
These features are fine by default but I would recommend adjusting most of them to help increase security and so that it runs exactly how you want it to. Remember this SSH server allows people to gain access to your files via SFTP and SSH allows access to command prompt where alot of damage can be done.

SSH Settings

This is where all the main SSH settings are configured in relation to the actual SSH server, the listening address and port number is the actual IP address and port the server will listen for communication data. We can also limit the max connections and idle timeout so that people can’t stay logged in forever. You can set a custom message in the banner message text field which will display to the user once they login, the command shell is the actual application which the user will see when logging into SSH. The RSA and DSA key are used during public and private key authentication, if these keys where to get lost or compromised this is where you can generate new ones so that the old ones no longer work.

Host restrictions
These options allow you to provide a list of IP addresses and IP address ranges, you can either allow or refuse this list of addresses. If you are always going to be connecting from a single or group of IP addresses its best to limit the SSH server to only allow connections from the IP addresses which you will be using, this will limit the chance of unauthorised login.

Logging
Keeping a log is very important as your able to back track who has logged in what they did, this is very important as you can get the IP addresses of any potential attacks and block them either via the host restrictions or firewall.

Online Users
This simple just allows you to see who is currently logged on, if you have installed the server as a services this will now show you if any users are logged in.

Automatic Updates
I would always recommend keeping up-to-date especially with security issues always arising, if you are planning on having this SSH server running all the time I wouldn’t use the auto update feature as if something goes wrong you may not be able to gain access to your server again.

Authentication
SSH servers support two types of authentication password and public key authentication, this section allows you to specify what types of authentication your SSH server will accept. I have written various articles related to SSH which can be found here.

SSH Password v Public/Private Key Authentication

Creating an SSH connection using password authentication

Creating an SSH connection using public/private authentication

Encryption
All traffic is encrypted including whilst logging in, multiple encryption methods are supported but unless you have a reason for using a specific type this option should just be set to auto.

Tunnelling
SSH servers also have the ability to use port forwarding which allows a user to transfer data going to a specific port on their side to the SSH server, the options here allow you to specify if local port forwarding and remote port forwarding is allowed. Local forwarding is when you transfer data on a port from your local machine to the SSH server, remote forwarding is the complete opposite where you direct a port on the SSH server your local machine.

20th July 2011

Scotland Holiday

Just thought I would let you all know how my holiday in Scotland is going and that as soon as I get back I will be creating more posts. Ive already got a bunch of PHP posts I need to write up or finish so be ready for a wave of posts.

Scotland is an amazing place if you love mountains, lochs and waterfalls you have to be willing to put up with sunless days, wind and rain but thats just scottish weather in one. Some of the roads aren’t great and quite dangerous. We are staying in Fort William and the main road which leads into the highlands is literally only big enough to fit two cars down side by side even though this road is being used by trucks, cars, lorries, mobile homes and anything else which goes on a road. You’ve got to be really vigilant to whats coming or a collision could happen easily; we almost has a crash due to a woman deciding she was going to pull into a layby last minute causing the car in front to do an emergency stop and then me. I was literally 1 car length away and ended up about 30cm from hitting the car in front (April, my girlfriend is to scared to go on these types of roads so i have to take over driving).

Just before we left I purchased a Canon 500D DSLR which came with the default lense and a 75-300mm lense due to Jessops having a special offer on. Because April has her own fashion blog and wanted a lense suitable for the pictures she wants, we bought a 50mm 1.8 lense which cost £95 from Jessops which is canons cheapest lense.

Here is some pictures we have taken and a video of a waterfall all taken with the Canon 500D DSLR camera. You can view all the pictures which have been taken from my picture gallery located here.

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27th June 2011