Picture Frames and Captions with ImageMagick

This article discusses some of the caption and border effects available with the ImageMagick image processing package. ImageMagick is freely available for Linux and Windows. It offers a huge number of image processing options, so many in fact, that using the program can be a little tricky.

The following examples were evolved from the ImageMagick online documentation, plus a good deal of trial and error to get the details right. I used Linux, but the same commands should work under Windows. Continue reading

Solaris Tictimed Catastrophic File Error

Solaris administrators may have seen the message “Catastrophic file error – zero length” in their system logs. Although it sounds serious, there is nothing “catastrophic” about it. This post explains how to stop the message from flooding your log files. Continue reading

An Example of Parallel Processing

This post shows how to use parallel processing to get a CPU intensive job done faster in Unix/Linux. By splitting a large task into several parts, it is quite easy to give each part to a separate CPU, and complete the task many times faster than it would on a single processor.

These days, even small PCs and other devices often come equipped with several CPU cores. But some tasks will use only one core, sometimes using 100% of it, while other cores stand by idle. Sometimes this is a waste of resources. Continue reading

bc Rounding Errors

There must be a few people out there who still use bc as a desk calculator. bc is a simple application that comes as standard on most unix and linux systems. It’s nicer to use than a graphical calculator app: less fussy, no mouse needed and you can see what you have typed.

bc Gets it Wrong

A recent mix-up with financial calculations lead me to discover that – unbelievably – bc was getting its sums wrong. This post explains the problem. Continue reading

SSH Authentication and Directory Permissions

Running sshd in the foreground can be an effective way to debug ssh problems. In the following example, a user was unable to access a remote system using ssh keys. Running sshd in debug mode provided a quick resolution. Both source and target systems were Solaris, but the same method applies equally to Linux. Continue reading

Huge Apache Error Log from Solaris 10 LicenseWatcher

Working on a client site recently, I noticed their Apache error log had grown to 32 Gb in size. The file was being written to at a rate of a quarter of a million lines a day, propelled by various cron jobs set up to run every 5 minutes. A PHP reconfiguration fixed the problem.

The box was a Solaris 10 system running “License Watcher“, and those messages was all coming from the License Watcher php code. Not genuine errors, just repeated diagnostics. I edited /usr/local/php/lib/php.ini and changed this line Continue reading

Check Free Memory on an LDOM Server

How to find the memory on a Solaris system hosting primary and guest LDOMs

For capacity planning, it is useful to know how much free resource is available on a given LDOM server. That is, a “parent” system hosting several guest LDOMs. For example, if you want to know how many more LDOM’s the server could support. Continue reading

Recovering Data from a Corrupted SD Card

SD cards are used in digital cameras, phones and other devices, where their speed and large capacity makes them useful for storing pictures, video and other voluminous multi-media items. It is quite common these days for a mobile device to contain a 16 Gb or 32 Gb SD card.

With the devices being so mobile, backups are easily overlooked. And it is quite easy for an SD card to become corrupted, for example if the card is removed while the device is on, or the battery is taken out while a video is being shot.

I was given a corrupted 16 Gb card and asked to recover the files, if possible. The rest of this post explains how the data was safely restored using simple Linux tools. Continue reading