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So you are installing a modern version of php using one of the alternative repositories, and suddenly you are confronted with a confusing choice. You want support for mysql (mysqli or PDO-mysql) in your php program. But which one to choose?

First off, you should probably be using PDO. It's just a cleaner database interface when compared to mysqli, and also tends to be the supported option if you're using an ORM like Doctrine2.

But you probably have found that installing the PDO package doesn't get you support for MySQL.

So what are these 2 packages? Well let's see what yum under Centos shows us, once we've setup webtatic as a repo:



In short, the mysql extension aka the mysql library is to quote Oracle/mysql

... a general-purpose client library

named libmysql.

This was the original php approach to supporting mysql. MySQL provided a client api library, and using that c library, a php extension was created that depends upon libmysql implementing the famous mysql_ functions that allowed php to talk to mysql.

The mysqlnd package (where nd stands for "native driver") is the fruit of a project to make mysql work optimally in the php language. Again to quote the mysql site:

The mysqlnd library is highly optimized for and tightly integrated into PHP. The MySQL Client Library cannot offer the same optimizations because it is a general-purpose client library.

The mysqlnd library is using PHP internal C infrastructure for seamless integration into PHP. In addition, it is using PHP memory management, PHP Streams (I/O abstraction) and PHP string handling routines. The use of PHP memory management by mysqlnd allows, for example, memory savings by using read-only variables (copy on write) and makes mysqlnd apply to PHP memory limits.

On top of these benefits are a number of interesting enhancements and support for plugins that might be of specific interest to you as a developer or sysadmin.

In general nothing should break in your code as the api should work the same under mysqlnd as it did with the old mysql library.

Conclusion

In summary, you want to use mysqlnd now and in the future.

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At some point I found some code to get the git branch name and insert it into the shell prompt. As it was some years ago, sadly I've forgotten the original source, but it wasn't exactly the type of prompt I'm used to, so I tweaked it until I got it the way I prefer. In the first set of brackets, I display the user@host:directory.

Once I cd into a git initialized directory a colored prompt appears with the branch name displayed in gold. For my purposes, this is simple, functional and doesn't result in overly long prompts. Here's what you can expect from any terminal that supports ansi color codes.



To implement the prompt on your server or workstation, simply cut this snippet and paste it into the end of the /etc/bashrc file.

The current way to do this is to create a new file named "gitprompt.sh" in the /etc/profile.d directory, and paste the code below into it. Using vim is a good way to accomplish this task. You need to be root or sudo for this to work of course.

Once the file exists, all the system users will benefit from the prompt in their shell sessions.

Using this prompt, whenever you're in your bash shell, there will be no question of whether or not you are in a git initialized directory, or what your currently checked out branch name is.



Does this work on a Mac? Yes of course!

I have been fighting a problem with mounting volumes from an NFS Server in AWS for a few days. With more pressing issues at hand, I had to try and google for solutions for an hour or so before bed, and nothing I was doing was having any effect. Curiously, an Ubuntu based machine that was mounting the drive using NFS3 was not having the same problem. Only the Amazon Linux servers that were using NFS4 were having the issue, and were showing all files and directories as being owned by nobody:nobody.



I had previously insured that the user UID and group GID for the user that would be writing files (in my case "apache" was the same (with the same UID and GID) on the NFS server and the servers mounting the nfs volume.

As it turned out the problem was with the configuration (or lack thereof) of the rpcidmapd service. NFS4 relies on this service to map users between machines. The "idmapd" requires that the domain of both the client and server should match for the UID/GID mapping to work, and in my case it wasn't. Probably many people with proper DNS configuration don't hit this problem, but we did not have a proper DNS setup, as these machines are part of a growing cluster. Compounding the problem I had set the configuration files to have meaningless host names rather than a domain.

You can tweak this setup by editing the: /etc/idmapd.conf file, and find the "Domain" variable:



Set these to be the same for the server and all the clients.

The last problem was that I had to restart the idmapd process, which has an /etc/init.d control script named /etc/rpcidmapd



Restart the process on both the nfs server and any nfs clients. If the source of your problem is the same as mine, your user & group mapping problems should be solved:



Finally!!!!

If you use a Windows based workstation or notebook computer virtualization offers a way for you to run a linux server environment using the same linux distribution and configuration you'll use in production. Virtualization allows you to explore clustering and network setups that can't be tested on your workstation alone and simplifies your development environment by keeping the LAMP environment contained inside a VM.

While VMWare offers these capabilities with their VMWare workstation product, Sun has created a free alternative called VirtualBox, with many of the same capabilities in VMWare workstation. VirtualBox runs on a variety of intel chip based operating systems including OS/X, Windows XP & Vista, Linux and Solaris, and supports the installation of many different "Guest" operating systems. In this article, I'll detail the installation and configuration of Centos. Centos is a great choice for a Linux server operating system, as it is widely used by hosting companies due to its Redhat Enterprise Linux (RHEL) core.

Our goals in this setup will be:

• Centos server running the LAMP stack
• XP can be used to develop code using the IDE of your choice.
• The XP Workstation can communicate with the linux server using standard tools: putty, winscp, firefox
• The setup works even when no other networking is available. When a network is available, no network reconfiguration is required.
• Use XP to setup private domain resolution so apache vhost configurations can be tested.

Let's get started.

Continue reading "Run a Centos Lamp development server on XP, Vista or Win 7 using VirtualBox"

This error pops up for a couple of reasons. At the top of the script there will probably be a line that looks like this:



This is telling Linux that this script should be interpreted using the /bin/sh program. So your first step is to verify that program exists. I tend to use:



This will typically come back with a response like this:



This is telling us that the path to the sh program is in fact /bin/sh, matching the path specified at the top of the script. Ok, so what gives? Well, it's possible that this script was made on an operating system that has line ending characters different than linux. This could have been on on a Mac or PC, or the file could have been converted when it was packaged. In this case, you get the relatively misleading bad interpreter: No such file or directory message, which is really trying to look for sh, although you don't get any indication of the fact.

So, how to fix? Read on. Continue reading "Linux shell scripting: bad interpreter: No such file or directory"

I gave a talk on the use of Xen for web developers at Lampsig. It took me a while to get my notes transcribed, but here at last they are. This prescription has been used by me to install Xen successfully on a Fedora core 4 box, Centos 4.3 and 4.4 boxes, and should probably work on RHEL, assuming you can figure out how to get the packages you need.

I cover use of file backed file systems, and how to mount and edit them, as well as expanding a file based filesystem.

I have run gentoo and Centos guests I got from jailtime.org and have found them to be very stable. I even was able to use this on a 64 bit server, although I did have to build my own guest. Many people who have had trouble getting Xen to work reliably when using the packaged (rpm) versions of Xen may find this prescription fixes their problems.

Xen 3.0 Centos How-to