Welcome to The Linux Page

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This site is a collection of my own work with Linux. Certain things are easy, others take time to decipher and if I ever need to repeat the work (which usually happens!), then I need to remember everything by memory or... have a site with all the steps taken and to take again.

The following are my most recent posts:

Error: acpid input device has been disconnected

USB Port Locked between Host & VirtualBox Guest

Today I experience the death of my mice, where my two mice completely stopped working. I tried to unplug and re-plug, but that did not help (once in a while, it helps for one of my mice which has a USB to PS/2 converter).

Restarting X11 may have been a solution, but on Ubuntu 18.04, that has never worked. That is, when I try to do the Ctrl-Alt-F1 to go to text and then come back with Alt-F7 or Alt-F8, the coming back portion doesn't work at all (i.e. it does not come back to X11 anymore, it tries, I can see the screen being switched, but it's not really doing anything).

Then I ...

Sleeping like a dragon is not compatible with most software now a day...

I wrote software that runs a video service. That means I need to have code that handles video frames in realtime. For that purpose, I compute when the next frame is expected to "hit".

More or less, like most such software, I compute the time for the next frame which tells me whether I have time to wait or not.

next-frame = start-frame + interval * frame-number

When you write proper software next-frame is going to be in the future (i.e. you have enough CPU time to idle for a bit). That means you want to wait until that time to then send the next frame.

nanosleep(next-frame - ...

Today I started to really have a need to be able to lower a window in MS-Windows without having to raise all the other windows in the right order. It is rather unfortunate that clicking a window forces it to be raised in the first place, X-Windows is way better for that since day one, but on top of that, there is no button to lower a window.

Okay so under Linux there is no button on the window to lower it, but you can middle click on the title bar and the window goes behind all the others (and yes, that happens by mistake once in a while, but the 99.9% of the time I use it right, it's a ...

Transporting PostgreSQL

When moving a database from one computer to another, you've got to copy all the data.

For that purpose PostgreSQL offers a pair of functions named pg_dump and pg_restore.

In most cases that works great, however, some applications may create things such as additional functions that will NOT make it across. I do not know how to get that to work (and maybe it works in newer version of PostgreSQL?)

In any event, in most cases the following commands are enough (I used them with Drupal websites and since they stopped using some of the definitions they have in the system.install file used on ...

Long command can be written as separate strings in cmake

Today I really wanted to write a command on multiple lines because I pass many command line options to it and it started to look really very long (much wider than my editor width).

There are many entries on how to run multiple commands: write one ADD_CUSTOM_COMMAND() per command. Simple enough. If you really only want one single ADD_CUSTOM_COMMAND(), you can always write a shell script (a .sh file) and put all the commands in there.

However, writing a single command with many command line options separated by spaces on multiple line is not well explained in the ADD_CUSTOM_COMMAND() ...

Creating a PDF and "attach" another PDF

Merging PDF files together

Now that I have an HP scanner that directly generates PDF files, I have a new problem:

In some cases. I scan multiple documents and get separate PDF files. Later I need to merge those separate PDF files together to form a single PDF that I can share with others.

The Poppler project actually includes the perfect tool for this purpose. Here is the command one uses to do the merging:

pdfunite in-1.pdf in-2.pdf ... in-n.pdf out.pdf

Voilà!

Now out.pdf is one single PDF composed of all the input PDFs 1 to n.

Old insulator installation

The .install File

The default manner in installing files in a Debian or Ubuntu package is to create a <package-name>.install file. That file has an extremely simple format that goes like this:

You can repeat this for each and every file you want to install.

99% of the time, that works great and I tend to use it a log.

There are several issues with the default format in this file:

1. Path Variation

The path to the files changes if you have a single package or if you have two or more. In the ...

Extending "less"

Endless Pier, Endless Possibilities with less

Adding More Support for Binaries

The less tool does a lot more than just show plain text files now a day.

This is done by piping the output of one or more commands run against the input, instead of directly showing said file contents.

The extension works through a set of variables named LESSOPEN and LESSCLOSE.

The LESSOPEN has a pipe at the start, end the name "lesspipe" for the script doing the heavy lifting:

| /usr/bin/lesspipe %s

The idea is for that script to write the results you want less to display to stdout.

So for example that script could do:

echo ...

Change your VirtualBox VM Icon

Iconic Chess Pieces

Changing a Virtual Machine (VM) Icon

By default, VirtualBox assigns a default icon to your VMs. That icon appears in your bar of icons (usually on the left side of the screen) and also in the VirtualBox interface.

If you just have one or two VMs, that's certainly not a huge issue. When you have 50 to 100, it becomes tedious to know what's what since all the icons will look alike (by default, they select the icon based on the operating system defined for that VM).

The solution is to assign a new icon to your VMs.

First, make sure that your icon is a square such as 48x48, 96x96, ...

Colors in Hexadecimal

See Binary File Contents

The Linux system comes with a tool named xxd, which is very useful to print binary files to a list of hexadecimal bytes.

It is pretty well thought of. I had my own atype command, but I now tend to use xxd because it's by default on most Linux systems, so no need to compile & install my own tool.

The most interesting feature, which I found out today, is that the tool is capable of doing the inverse (see the -r option): it can read its own output and generate a binary file again. It actually doesn't need to be output from xxd, just hexadecimal codes.

Unfreeze your Mouse when it Froze

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The .install File

1. Path Variation

Adding More Support for Binaries

Changing a Virtual Machine (VM) Icon

See Binary File Contents