Archive for Web Development

Basic string searching in MySQL table columns

April 29, 2010 One comment

Last weekend, I ended up doing a spot of file structure reorganisation on the web server for www.johnhennessy.co.uk and needed to correct some file pointers in entries on my outdoors blog. Rather than grabbing a plugin from somewhere, I decided to edit the posts table directly. First, I needed to select the affected observations and this is where I needed to pick out the affected rows and edit them in MySQL Query Browser. To do that, I needed basic string searching so I opened up my MySQL eBook from Apress and constructed something like the following:

select * from posts_table where post_text like ‘%some_text%’;

The % wildcard characters are needed to pick out a search string in any part of a piece of text. There may be more sophisticated method but this did what I needed in a quick and dirty manner without further ado. Well, it was what I needed.

Databases, Scripting, Software, Web Development

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Removing a column from a MySQL data table

April 19, 2010 No comments

My trying out WordPress 3.0 in advance of its final release has brought me errors on the links management page. After a spot of poking around the TRAC, I found that the bug already has been reported and that the cause is an extraneous column in the *_links table called link_category. The change in taxonomy handling over the years seems to have made it redundant so I removed the said column from the database using a command like the following from both the MySQL command line and MySQL Query Browser:

alter table wordpress.wp_links drop link_category;

That seems to have made those errors go away and I hop that their upgrade code takes care of this before WordPress 3.0 is let loose of the general blogging public. Taking out the coding brittleness would do too.

Databases, Web Development, Web Technologies, Web Tools

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Relocating the Apache web server document root directory in Fedora 12

April 9, 2010 No comments

So as not to deface anything that is available online on the web, I have a tendency to set up an offline Apache server on a home PC to do any tinkering away from the eyes of the unsuspecting public. Though Ubuntu is my mainstay for home computing, I do have a PC with Fedora installed and I have been trying to get an Apache instance starting automatically on there without success for a few months. While I can start it by running the following command as root, I’d rather not have more manual steps than is necessary.

httpd -k start

The command used by the system when it starts is different and, even when manually run as root, it failed with messages saying that it couldn’t find the directory while the web server files are stored. Here it is:

service httpd start

The default document root location on any Linux distribution that I have seen is /var/www and all is very well with this but it isn’t a safe place to leave things if ever a re-installation is needed. Having needed to wipe /var after having it on a separate disk or partition for the sake of one installation, it doesn’t look so persistent to me. In contrast, you can safeguard /home by having it on another disk or in a dedicated partition and it can be retained even when you change the distro that you’re using. Thus, I have got into the habit of having the root of the web server document root folder in my home area and that is where I have been seeing the problem.

Because of the access message, I tried using chmod and chgrp but to no avail. The remedy has to do with reassigning the security contexts used by SELinux. In Fedora, Apache will not work with the context user_home_t that is usually associated with home directories but needs httpd_sys_content_t instead. To find out what contexts are associated with particular folders, issue the following command:

ls -Z

The final solution was to create a user account whose home directory hosts the root of the web server file system, called www in my case. Then, I executed the following command as root to get things going:

chcon -R -h -t httpd_sys_content_t /home/www

It seems that even the root of the home directory has to have an appropriate security context (/home has home_root_t so that might do the needful too). Without that, nothing will work even if all is well at the next level down. The switches for chcon command translate as follows:

-R : recursive; applies changes to all files and folders within a directory.

-h : changes apply only to symbolic links and not to where they refer in the file system.

-t : alters context type.

It took a while for all of this stuff about SELinux security contexts to percolate through to the point where I was able to solve the problem. A spot of further inspiration was needed too and even guided my search for the information that I needed. It’s well worth trying Linux Home Networking if you need more information. There are references to an earlier release of Fedora but the content still applies to later versions of Fedora right up to the current release if my experience is typical.

Linux, Security, Software, Web Development

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Easier to print?

February 20, 2010 No comments

One matter that really came to light was how well or not the pages on here and on my hill walking and photography website came out on the printed page. After spotting a WordPress Codex article and with an eye on making things better, I have made a distinction between screen and print stylesheets. The code in the XHTML looks like this:

<link rel=”stylesheet” href=”/style.css” type=”text/css” media=”screen” />
<link rel=”stylesheet” href=”/style_print.css” type=”text/css” media=”print” />

The media attribute seems to be respected by the browsers that I have been using for testing (latest versions of Firefox, MSIE and Opera) so it then was a matter of using CSS to control what was shown and how it was displayed. Extraneous items like sidebars were excluded from the printed page in favour of the real content that visitors would be wanting anyway and everything else was made as monochrome as possible with images being the only things to escape. After all, people don’t want to be wasting paper and ink in this cash strained times and there’s no need to have any more colour than necessary either. Then, there’s the distraction caused by non-functioning hyperlinks that has inspired the sharing of some wisdom on A List Apart. Returning to my implementation, please let me know in the comments what you think of what I have done on here and if there remains any room for improvement.

Web Development

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Another look at Drupal

January 20, 2010 One comment

Early on in the first year of this blog, I got to investigating the use of Drupal for creating an article-based subsite. In the end, the complexities of its HTML and CSS thwarted my attempts to harmonise the appearance of web pages with other parts of the same site and I discontinued my efforts. In the end, it was Textpattern that suited my needs and I have stuck with that for the aforementioned subsite. However, I recently spotted someone very obviously using Drupal in its out of the box state for a sort of blog (there is even an extension for importing WXR files containing content from a WordPress blog); they even hadn’t removed the Drupal logo. With my interest rekindled, I took another look for the sake of seeing where things have gone in the last few years. Well, first impressions are that it now looks like a blogging tool with greater menu control and the facility to define custom content types. There are plenty of nice themes around too though that highlights an idiosyncrasy in the sense that content editing is not fully integrated into the administration area where I’d expect it to be. The consequence of this situation is that pages, posts (or story as the content type is called) or any content types that you have defined yourself are created and edited with the front page theme controlling the appearance of the user interface. It is made even more striking when you use a different theme for the administration screens. That oddity aside, there is a lot to recommend Drupal though I’d try setting up a standalone site with it rather than attempting to shoehorn it as a part of an existing one like what I was trying when I last looked.

Blogging, Software, Web, Web 2.0, Web Development, Web Technologies, Web Tools

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Securing MySQL in Fedora

December 4, 2009 One comment

Ubuntu users must be spoilt because any MySQL installation asks you for a root password, a very good thing in my opinion. With Fedora, it just pops the thing on there with you needing to set up a service and setting the root password yourself; if I remember correctly, I think that openSUSE does the same thing. For the service management, I needed to grab system-config-services from the repositories because my Live CD installation left off a lot of stuff, OpenOffice and GIMP even. The following command line recipe addressed the service manager omission:

su – # Change to root, entering password when asked
yum -y install system-config-services # Installs the thing without a yes/no prompt
exit # Return to normal user shell

Thereafter, the Services item from the menus at System > Administration was pressed into service and the MySQL service enabled and started. The next step was to lock down root so the following sequence was used:

mysql # Enter MySQL prompt; no need for user or password because it still is unsecured!
UPDATE mysql.user SET Password=PASSWORD(‘MyNewPass’) WHERE User=’root’;
FLUSH PRIVILEGES;
quit # Exit the mysql prompt, leaving the bare mysql command unusable

For those occasions when password problems keep you of the MySQL shell, you’ll find password resetting advice on the MySQL website but I didn’t need to go the whole hog here. MySQL Administrator might be another option for this type of thing. That thought never struck me while I was using it to set up less privileged users and allowing them access to the system. For a while, I was well stymied in my attempts to access the MySQL using any of those extra accounts until I got the idea of associating them with a host, another thing that is not needed in Ubuntu if my experience is any guide. All in all, Fedora may make you work a little extra to get things like thing done but I am not complaining if it makes you understand a little more about what is going on in the background, something that is never a disadvantage.

Databases, Linux, Scripting, Software, Web, Web Development, Web Technologies

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