Linux Tips, Tricks, Tutorials & Fixes

Xen is a virtualization system supporting both paravirtualization and hardware-assistant full virtualization. Xen is an open-source type-1 or baremetal hypervisor, which makes it possible to run  many instances of an operating system or indeed different operating systems in parallel on a single machine (or host). Xen is the only type-1 hypervisor that is available as open source. Xen is  used as the basis for a number of different commercial and open source applications, such as: server virtualization, Infrastructure as a Service (IaaS), desktop virtualization, security  applications, embedded and hardware appliances.  Some main points on Xen: It named from neXt gENeration virtualization. Xen initially created by University of Cambridge Computer Laboratory. Xen is Open source (Licensed under GPL2). Xen offers high performance and secure architecture. Xen is powered by a growing and active community and a diverse range of products and services. ...

If your hosting has put a limit on simultaneous MySQL connections per account, you will get Database Connection error on your website when your database connections exceed limit on the server. It depends upon your database queries connections hitting to the server. Most sites will work perfectly with a 25 concurrent processes limit. Processes open and close so quickly that they hardly ever overlap. If your website is exceeding the database connection limit, you need to optimize your database (for faster queries). Also, you should check your code to see if you are closing the connections correctly. the connections can also be there because you use pooling, so the system can reuse exist connections. I am pasting some techniques to optimize your database: 1)  long-running process on MySQL Please do a query level optimization to avoid long running queries. i) http://dev.mysql.com/doc/refman/5.0/en/kill.html ii) http://rugmonster.org/2009/02/kil...

Sometime, httpd service is being stopped in the service due to mime types files. When you will check the logs, you will get the following error: root@server [~]# tail -f /usr/local/apache/logs/error_log [Wed May 08 17:08:25 2013] [error] (2)No such file or directory: could not open mime types config file /usr/local/apache/conf/mime.types. Configuration Failed Fix: In such scenario, you can fix the issue by copying the mime.types files from /etc directory to /etc/httpd/conf/ or /usr/local/apache/conf (In cPanel server). root@server [/etc]# cp -iv mime.types /usr/local/apache/conf/ `mime.types' -> `/usr/local/apache/conf/mime.types' root@server [/etc]# Then start httpd as follows: root@server [/usr/local/apache/conf]# /etc/init.d/httpd start root@server [/usr/local/apache/conf]# The httpd service is started now. :)