A handy document that has not all but most frequently used shortcuts for vi on Bash.
http://www.catonmat.net/download/bash-vi-editing-mode-cheat-sheet.pdf
Credits to Peteris Krumins.
Shortcuts Cheat Sheet for “vi”
Performance vs. Efficiency
While doing a research on both terms above I did come up with 2 great resources on the internet. Basically, performance is a measurable aspect determining how “fast” or “quick” your item completes a task, however, efficiency does focus on the “way you utilize your resources” to produce the outcome. Therefore a high-performance system does not necessarily need to be high-efficient. On the other hand, in general efficiency is considered to be a component in the classification of performance.
Swollen MacBook Battery – Possible Fix
It definitely is a disturbing issue because the swollen battery does not only lift your MacBook a few millimeters up but also makes the trackpad almost unusable. I do not know why this happens but there are plenty of people out there on the internet having the same issue.
So far I have 2 options, to purchase a new battery, or try something unusual first – that only one person so far has provided information on how to do it – open up the battery, let the expanded gas flow out and try again.
I will go with the 2nd option initially. You may find the article on wordpress: http://lepageblog.wordpress.com/2011/11/24/how-to-fix-a-swollen-macbook-battery/
JSP sendRedirect Causes IllegalStateException
IllegalStateException
I am about to finalize my mini-Service Desk project called TTS for one of my Master’s course and wanted to share an important notice on using sendRedirect on your JSP pages.I use GlassFish Server 3.1.1
I have plenty of redirections throughout the application using both POST and GET methods and I paused for a few seconds when I received a java.lang.IllegalStateException during one of them.
Suddenly I realized the issue: once you are using a redirect make sure the application returns before going into another redirection:
boolean res = port.isTechnicianExists(TechnicianName);
if (res){
response.sendRedirect("../createuser.jsp?action=createUser&status=ERR&message=Username_already_exists");
return;
}
Administration: Server Becomes Unresponsive Sporadically [Solved]
SSH - pstree
I have been facing with a weird issue lately – completely sporadically. My server has been becoming unresponsive once every week – besides it is not only HTTP (Apache) that cannot accept any connections but also other services such as SSH, Email Server or even system activities such as crontab. This has been a very annoying situation indeed, and all I could do was to pray that the login via SSH does not exceed the 20 seconds timeout period that I had set for security purposes. But it always did. Only option was to connect to Webmin interface, and take the appropriate actions to take the server back to life.
I did suspect it was a memory issue – and I was right, Apache was the only reason. After installing WordPress I had observed a massive increase in load on MySQL and HTTP servers but the problem was that Apache was creating way too many threads for each connection it established. I checked the configuration files and probably WordPress had added some directives regarding these settings. Modifying it according to my needs have resolved the issue:
## ## Server-Pool Size Regulation (MPM specific) ## # prefork MPM # StartServers: number of server processes to start # MinSpareServers: minimum number of server processes which are kept spare # MaxSpareServers: maximum number of server processes which are kept spare # MaxClients: maximum number of server processes allowed to start # MaxRequestsPerChild: maximum number of requests a server process serves <IfModule mpm_prefork_module> StartServers 2 MinSpareServers 25 MaxSpareServers 25 MaxClients 150 MaxRequestsPerChild 0 </IfModule> # worker MPM <IfModule mpm_worker_module> StartServers 2 MinSpareThreads 25 MaxSpareThreads 25 ThreadLimit 25 ThreadsPerChild 12 MaxClients 150 MaxRequestsPerChild 0 </IfModule> # event MPM <IfModule mpm_event_module> StartServers 2 MaxClients 150 MinSpareThreads 25 MaxSpareThreads 25 ThreadLimit 50 ThreadsPerChild 12 MaxRequestsPerChild 0 </IfModule>
Send Email – Authentication Error using Net::SMTP::SSL
I have been creating a simple monitoring tool for my server (alkankoray.net) at home using Perl and during that process I have come up with an error occured while I was trying to send email using Secure SMTP via Google Mail although all the account information was correct and the code appeared to be OK:
if (not $smtp = Net::SMTP::SSL->new('smtp.gmail.com',
Port => 465, Debug => 1))
die "Server Connection Error";
$smtp->auth(" [account login] ", " [ account password ] ")
|| die "Authentication Error";
The issue was related to a missing component: SASL.
Apt-getting it resolves the issue – no clear description and reason in the debug output for the failure, but that is the solution.
sudo apt-get install libauthen-sasl-perl
Building a Simple Web Service Using SOAP on PHP
My webserver is running on Ubuntu 9.10 with PHP 5.2.6 and I suppose you will not be facing with any problems if you are running the same or higher versions.
Preconditions: Apache Web Server 2.2 and PHP5 is installed on your system. If you do not know how to accomplish that, I recommend doing a search on Google with “installing php on linux”.
First thing is to install the SOAP extension on PHP. To do that, simply type “sudo apt-get install php-soap”. Now, what we will be building is a simple HTML form (client.html) with a Name and Surname text field, posting data to a PHP page (client_submit.php), and a web service server page that will process the request and return the result back to the client (server.php).
1. Create the client.html with the following code:
<html> <head><title>Web Service Test</title></head> <body> <form name="test" action="client_submit.php" method="POST"> Name: <input type="text" name="in_name"><br> Last Name: <input type="text" name="in_lastname"><br> <input type="submit" name"submit"> </form> </body> </html>
2. A very basic form to be submitted. Now, copy and paste the following code to client_submit.php, the page HTML will post to:
<?php
$name = $_POST["in_name"];
$lastname = $_POST["in_lastname"];
$client = new SoapClient(null, array('location' => "http://www.alkankoray.net/webservice/server.php",
'uri' => "http://www.alkankoray.net/webservice"));
$result = $client->__call("welcomeMessage",array($name,$lastname));
echo $result;
?>
This will create a new SoapClient and call the welcomeMessage on Server getting the return value of it, and display it. Please change the location and uri according to your configuration.
3. Copy & Paste the code below to your server (server.php):
<?php
function welcomeMessage($myname, $mylastname){
return "Welcome " . $mylastname . ", " . $myname;
}
$server = new SoapServer(null, array('uri' => "http://www.alkankoray.net/webservice"));
$server->addFunction("welcomeMessage");
$server->handle();
?>
Here the welcomeMessage function and the SOAP server is defined, function added to it.
SOAP Result
This was a 3-step quick tutorial on creating a basic web service. With this example both the client and server lies on the same server, however, of course this might not be the case. This is probably the most reliable and secure way to communicate through device-to-device on the internet. I will use these basics while developing a mobile application that needs to connect to the database on my alkankoray.net server, instead of using a local database such as SQLite.
