TOPIC: CROSS-PLATFORM SOFTWARE
Sorting out MySQL on Arch Linux
5th November 2011
Seeing Arch Linux running so solidly in a VirtualBox virtual box has me contemplating whether I should have it installed on a real PC. Saying that, recent announcements regarding the implementation of GNOME 3 in Linux Mint have caught my interest, even if the idea of using a rolling distribution as my main home operating system still has a lot of appeal for me. Having an upheaval come my way every six months when a new version of Linux Mint is released is the main cause of that.
While remaining undecided, I continue to evaluate the idea of Arch Linux acting as my main OS for day-to-day home computing. Towards that end, I have set up a working web server instance on there using the usual combination of Apache, Perl, PHP and MySQL. Of these, it was MySQL that went the least smoothly of all because the daemon wouldn't start for me.
It was then that I started to turn to Google for inspiration, and a range of actions resulted that combined to give the result that I wanted. One problem was a lack of disk space caused by months of software upgrades. Since tools like it in other Linux distros allow you to clear some disk space of obsolete installation files, I decided to see if it was possible to do the same with pacman, the Arch Linux command line package manager. The following command, executed as root, cleared about 2 GB of cruft for me:
pacman -Sc
The S in the switch tells pacman to perform package database synchronization, while the c instructs it to clear its cache of obsolete packages. In fact, using the following command as root every time an update is performed both updates software and removes redundant or outmoded packages:
pacman -Syuc
So I don't forget the needful housekeeping, this will be what I use from this point forward, with y being the switch for a refresh and u triggering a system upgrade. It's nice to have everything happen together without too much effort.
To do the required debugging that led me to the above along with other things, I issued the following command:
mysqld_safe --datadir=/var/lib/mysql/ &
This starts up the MySQL daemon in safe mode if all is working properly, and it wasn't in my case. Nevertheless, it creates a useful log file called myhost.err in /var/lib/mysql/. This gave me the messages that allowed the debugging of what was happening. It led me to installing net-tools and inettools using pacman; it was the latter of these that put hostname on my system and got the MySQL server startup a little further along. Other actions included unlocking the ibdata1 data file and removing the ib_logfile0 and ib_logfile1 files to gain something of a clean sheet. The kill command was used to shut down any lingering mysqld sessions too. To ensure that the ibdata1 file was unlocked, I executed the following commands:
mv ibdata1 ibdata1.bad
cp -a ibdata1.bad ibdata1
These renamed the original and then crafted a new duplicate of it, with the -a switch on the cp command forcing copying with greater integrity than normal. Along with the various file operations, I also created a link to my.cnf, the MySQL configuration file on Linux systems, in /etc using the following command executed by root:
ln -s /etc/mysql/ my.cnf /etc/my.cnf
While I am unsure if this made a real difference, uncommenting the lines in the same file that pertained to InnoDB tables. What directed me to these were complaints from mysqld_safe in the myhost.err log file. All I did was to uncomment the lines beginning with innodb and these were 116-118, 121-122 and 124-127 in my configuration file, but it may be different in yours.
After all the above, the MySQL daemon ran happily and, more importantly, started when I rebooted the virtual machine. Thinking about it now, I believe that it was a lack of disk space, the locking of a data file and the lack of InnoDB support that was stopping the MySQL service from running. Running commands like mysqld start weren't yielding useful messages, so a lot of digging was needed to get the result that I needed. In fact, that's one of the reasons why I am sharing my experiences here.
In the end, creating databases and loading them with data were all that was needed for me to start to see functioning websites on my (virtual) Arch Linux system. It turned out to be another step on the way to making it workable as a potential replacement for the Linux distributions that I use most often (Linux Mint, Fedora and Ubuntu).
Turning off the admin bar in WordPress 3.1
25th October 2010
Work on WordPress 3.1 is in full swing at the moment, though I initially thought that they were taking a little break after 3.0. From what I can see, many refinements are being made to the multi-blog functionality and behind-the-scenes work is ongoing on the administration screens too.
Another under-the-bonnet change has been to make WordPress less tied to MySQL, since the possibility of dropping in support for an alternative such as PostgreSQL is now a reality even if it isn't part of the default package. For now, it looks as if this will be plugin territory rather than default multi-database support, though that may become a sensible development in the light of Oracle's acquisition of MySQL and its sabre-rattling regarding Java patents. So far, the change to WordPress has affected my use of its database engine to power an offline version of my online photo gallery, but a quick spot of code editing sorted that issue.
One more obvious alteration will be the addition of a WordPress.com style administration bar to the top of all content and administration screens for a user who is logged into the system. Though it will be turned on by default, there will be the option of turning it off for those among who prefer things that way. All that will be needed for this is to add the following line near the top of wp-config.php:
define( "WP_SHOW_ADMIN_BAR", false);
The chance to see new additions like those above and be ready for is my main reason for following WordPress development. It's best to be ready instead of being surprised, though it has to be said that the blogging or CMS platform is a very polished one these days.
A look at Emacs
10th August 2010
It's remarkable what work can bring your way in terms of technology. For me, (GNU) Emacs Has proved to be such a thing recently. It may have been around since 1975, long before my adventures in computing ever started, in fact, but I am asking myself why I never really have used it much. There are vague recollections of my being aware of its existence in the early days of my using UNIX over a decade ago. Was it a shortcut card with loads of seemingly esoteric keyboard shortcuts and commands that put me off it back then? The truth may have been that I got bedazzled with the world of Microsoft Windows instead, and so began a distraction that lingered until very recently. As unlikely as it looks now, Word and Office would have been part of the allure of what some consider as the dark side these days. O how OpenOffice.org and their ilk have changed that state of affairs...
The unfortunate part of the Emacs story might be that its innovations were never taken up as conventions by mainstream computing. If its counterparts elsewhere used the same keyboard shortcuts, it would feel like learning such an unfamiliar tool. Still, it's not as if there isn't logic behind it because it will work both in a terminal session (where I may have met it for the first time) and a desktop application GUI. The latter is the easier to learn, and the menus list equivalent keyboard shortcuts for many of their entries, too. For a fuller experience though, I can recommend the online manual, and you can buy it in paper form too if you prefer.
One thing that I discovered recently is that external factors can sour the impressions of a piece of software. For instance, I was using a UNIX session where the keyboard mapping wasn't optimal. There's nothing like an unfamiliar behaviour for throwing you off track because you feel that your usual habits are being obstructed. For instance, finding that a Backspace key is behaving like a Delete one is such an obstruction. It wasn't the fault of Emacs, and I have found that using Ctrl+K (C-k in the documentation) to delete whole lines is invaluable.
Apart from keyboard mapping niggles, Emacs has to be respected as a powerful piece of software in its own right. It may not have the syntax highlighting capabilities of some, like gedit or NEdit for instance, but I have a hunch that a spot of Lisp programming would address that need. What you get instead is support for version control systems like RCS or CVS, along with integration with GDB for debugging programs written in a number of languages. Then, there are features like file management, email handling, newsgroup browsing, a calendar and a calculator that make you wonder if they tried to turn a text editor into something like an operating system. With Google trying to use Chrome as the basis of one, it almost feels as is Emacs was ahead of its time, though that may have been more due to its needing to work within a UNIX shell in those far-off pre-GUI days. It really is saying something that it has stood the test of time when so much has fallen by the wayside. Like Vi, it looks as if the esteemable piece of software is showing no signs of going away just yet. Maybe it was well-designed in the beginning, and the thing certainly seems more than a text editor with its extras. Well, it has to offer a good reason for making its way into Linux too...
Upgrading to Fedora 13
1st June 2010
After having a spin of Fedora's latest in a VirtualBox virtual machine on my main home PC, I decided to upgrade my Fedora box. First, I needed to battle imperfect Internet speeds to get an ISO image that I could burn to a DVD. Once that was in place, I rebooted the Fedora machine using the DVD and chose the upgrade option to avoid bringing a major upheaval upon myself. You need the full DVD for this because only a full installation is available from Live ISO images and CD's.
Since all was graphical easiness, I got back into Fedora again without a hitch. Along with other bits and pieces, MySQL, PHP and Apache are working as before. If there was any glitch, it was with NetBeans 6.8 because the upgrade from the previous version didn't seem as complete as hoped. However, it was nothing that an update of the open source variant of Java and NetBeans itself couldn't resolve. There may have been untidy poking around before the solution was found, but all has been well since then.
Basic string searching in MySQL table columns
29th April 2010
Last weekend, I ended up doing a spot of file structure reorganisation on the web server for my Assorted Explorations website 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 had to pick out the affected rows and edit them in MySQL Query Browser. To accomplish that, I needed basic string searching, so I opened up my MySQL e-book from Apress and constructed something like the following:
select * from posts_table where post_text like '%some_text%';
The % wildcard characters are required to pick out a search string in any part of a piece of text. There may be a more sophisticated method, but this did what I needed in a quick and dirty manner without further ado. Well, it was what I needed.
Further securing MySQL in Fedora
4th December 2009
Ubuntu users must be spoilt because any MySQL installation asks you for a root password, an excellent 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 recall 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 the root user, 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 out of the MySQL shell, you'll find password resetting advice on the MySQL website, though 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 on Ubuntu if my experience is any guide. All in all, Fedora may make you work a little extra to get things like thing done, yet 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.
Out of memory at line: 56
28th May 2009
This is an error that I have started to see a lot in the last few weeks. First, it was with Piwik and latterly with WordPress.com Stats. For the record, I have never seen it on up-to-date systems but always with IE6 and at page unloading time. The CPU usage hits 100% before the error is produced, which had me blaming JavaScript in error. However, it isn't the cause of all ills.
In fact, the cause seems to be a bug in a certain release of Adobe Flash 9, but I reckon that the inclusion of certain features in a Flash movie are needed to trigger it too. While I don't have the exact details of this, WordPress.com Stats worked without fault until a recent update, so that is what is making me reach the conclusion that I have. That observation also makes me wonder whether we are coming to a point where Flash compatibility is something that needs to be factored into the use of the said technology in a website or web application. Updating Flash will solve the problem on the client, but it might be better if it wasn't triggered on the server side either.
Understanding Perl binding operators for pattern matching
20th May 2009
While this piece is as much an aide de memoire for myself as anything else, putting it here seems worthwhile if it answers questions for others. The binding operators, =~ or !~, come in handy when you are framing conditional statements in Perl using Regular Expressions, for example, testing whether x =~ /\d+/ or not. The =~ variant is also used for changing strings using the s/[pattern1]/[pattern2]/ regular expression construct (here, s stands for "substitute"). What has brought this to mind is that I wanted to ensure that something was done for strings that did not contain a certain pattern, and that's where the !~ binding operator came in useful; ^~ might have come to mind for some reason, but it wasn't what I needed.
When web hosting limits become too restrictive
27th April 2009
Fasthosts has, in their wisdom, decided to limit the execution time for ASP scripts to 15 seconds and 10 seconds for any others. I haven't used Perl sufficiently in this shared hosting set up to determine how that is affected. In contrast, I can share my experiences on the PHP side and you may have noticed occasional glitches. They have also disabled the set_time_limit PHP function, so you cannot easily address the matter yourself where you need to do it. You almost get the feeling that they don't trust the abilities, actions and oversight of their users. Personally, I reckon that the ten-second limit is too short and that something of the order of 20 or 30 seconds would be better. If it all gets too restrictive, I suppose that there are other providers, though I think that I would avoid resellers after a previous less than glorious experience. There's the dedicated server option too if I was feeling flush, not so likely given the economic times in which we live.
On keyboards
17th April 2009
While there cannot be too many Linux users who go out and partner a Microsoft keyboard with their system, my recent cable-induced mishap has resulted in exactly that outcome. Keyboards are such standard items that it is not so possible to generate any excitement about them, apart from RSI-related concerns. While I wasn't about to go for something cheap and nasty that would do me an injury, going for something too elaborate wasn't part of the plan either, even if examples of that ilk from Microsoft and Logitech were sorely tempting.
Shopping in a bricks and mortar store, like I was, has its pluses and its minuses. The main plus points are that you see and feel what you are buying, with the main drawback being that the selection on offer isn't likely to be as extensive as you'd find on the web, even if I was in a superstore. Despite the latter, there was still a good deal available. Though there were PS/2 keyboards for anyone needing them, USB ones seemed to be the main offer, with wireless examples showcased too. Strangely, the latter were only available as kits with mice included, further adding to the cost of an already none too cheap item. The result was that I wasn't lured away from the wired option.
While I didn't emerge with what would have been my first choice because that was out of stock, that's not to say that what I have doesn't do the job for me. The key action is soft and cushioned, which is a change from that to which I am accustomed; some keyboards feel like they belong on a laptop, but not this one. There are other bells and whistles too, with a surprising number of them working. The calculator and email buttons number among these along with the play/pause, back and forward ones for a media player; I am not so convinced about the volume controls though an on-screen indicator does pop up. You'd expect a Microsoft item to be more Windows specific than others, yet mine works as well as anything else in the Ubuntu world and I have no reason to suspect that other Linux distros would spurn it either. Keyboards tend to be one of those "buy-it-and-forget-it" items, and the new arrival should be no different.