This series is written by a representative of the latter group, which is comprised mostly of what might be called "productivity users" (perhaps "tinkerly productivity users?"). Though my lack of training precludes me from writing code or improving anyone else's, I can, nonetheless, try and figure out creative ways of utilizing open source programs. And again, because of my lack of expertise, though I may be capable of deploying open source programs in creative ways, my modest technical acumen hinders me from utilizing those programs in what may be the most optimal ways. The open-source character, then, of this series, consists in my presentation to the community of open source users and programmers of my own crude and halting attempts at accomplishing computing tasks, in the hope that those who are more knowledgeable than me can offer advice, alternatives, and corrections. The desired end result is the discovery, through a communal process, of optimal and/or alternate ways of accomplishing the sorts of tasks that I and other open source productivity users need to perform.

Friday, July 18, 2014

Miscellaneous Friday quickies: The Plop boot manager; what is it and why would you need it?

Prefatory remark: I am uncertain of the licensing status of the project discussed in the posting below, but I suspect it may not--unlike most of the other utilities I discuss in this blog--be open-source.

Unless you, like me, are stubbornly trying to repurpose aging hardware, this tool might not be of much interest to you. But it allowed me to get an older machine booting from USB when BIOS limitations were interfering, , so I decided to document here the fairly simple procedures I followed to accomplish this in case they might be of benefit to others.

How old was said machine? Well, old enough to not only have problems booting from USB flash drives (BIOS USB boot options were limited to USB floppies or ZIP disks), but to have a floppy drive in it as well! A single core machine, as you might guess, although the motherboard did at least have SATA headers--which made it a good candidate for the project I had in mind.

I learned, through some on-line research, about the Plop boot manager--touted for enabling systems to boot from USB even where BIOS settings limited it--and that floppy disk images of the boot manager are included in the download. So I dug up and dusted off a floppy, downloaded the image, and wrote it to the floppy the GNU/Linux way--using dd:

dd if=/path/to/plpbt.img of=/dev/fd0

And that disk did, in fact, allow me to boot sanely from a USB thumb drive I'd plugged into the system. On boot, a starfield simulation reminiscent of the old Star Trek intro (ok, I'm dating myself here) appeared on the screen, in the foreground of which was a boot menu from which I could select the medium I wished to boot. And, sure enough, USB was one of the items.

That wasn't quite all I needed for my own application, however; you see, my hope was to have this machine run headless. So, how to make the boot manager default to booting from the USB drive after a certain number of seconds?

For that, it turns out, I needed another program included in the download called plpbtcfg. That program is what allows one to modify the binary file plpbt.bin. And plpbt.bin needs to be accessed somehow as well in order to modify it--accomplished in my case by mounting plpbt.img as a looped file system.

So I ran mount -o loop /path/to/plpbt.img /mnt/loop. Once that image had been thus mounted, I cd'd to where I'd downloaded plpbtcfg and ran plpcfgbt cnt=on cntval=4 dbt=usb /mnt/loop/plpbt.bin: that gave the boot menu a four-second time count, after which the computer would automatically boot from USB. I rewrote, using dd again, that image, to the floppy. So, mission accomplished.

Except some other aspects of that machine's operation proved not very suitable to the application I was hoping to deploy it for, so I'm not sure it will finally be put into service. But that's another story . . .

Saturday, April 12, 2014

Miscellaneous Friday quickies: crop pdf margins with psnup

As sometimes happens, I recently needed to print off a portion of a public-domain work that's been scanned to portable document format and made available for download via Google Books. As the case proves to be at times, the original book had pages with fairly wide margins; when that sort of scanned book gets printed on letter-sized paper, you end up with a smallish text-box in the middle of a page that will have something like two-inch margins. That makes the text harder to read because the font ends up being relatively small, and it also results in waste of a lot of paper.

What to do, then, to make the text larger and make it occupy more of the page? I used three utilities for this job: xpdf to excise the target pages into a postscript file, psnup to enlarge the text and crop margins, and ps2pdf to convert the modified pages back to a pdf file. psnup is part of the psutils package, while ps2pdf relies on Ghostscript. A description of the steps I took follows.

With the pdf-viewer xpdf, the print dialog offer two option: print the document to a physical printer, or print to a postscript file. Both options allow for page-range stipulation. That's how I created a postscript file from the target pages.

Next, psnup--a really handy tool I've used previously for creating booklets (more about that in a future entry), but which I'd never considered might perform a job like this--was used to reduce margins, which had the added effect of increasing the text size. The command I used, which I appropriated from here, looks like this:

psnup -1 -b-200 infile.ps file_zoomed.ps

The crucial switch here seems to be -b (which is short for borders) followed by a negative numeral. Of course the numeral 200 as seen in this example will need to be modified to suit your circumstances.

The final step of converting file_zoomed.ps, using ps2pdf, to a pdf was simplest of all--in fact so simple that I won't even describe it here. I hope this brief description may be an aid to others wishing to execute a task like this.

Finally, I ran across some other related information of interest while reaserching how to crop pdf margins. Here, for example, is a page that describes a few other, more technically-involved ways to reduce margins: http://ma.juii.net/blog/scale-page-content-of-pdf-files. This posting on the Ubuntu forums has a really interesting script someone put together for making pdf booklets: http://ubuntuforums.org/showthread.php?t=1148764. And this one offers some clever tips on using another psutils utility--psbook--for making booklets: http://www.peppertop.com/blog/?p=35. Then, there's what might be the most straightforward utility of all for cropping pdf margins--pdfcrop. Since I could not get it to work for me in this instance, I looked for and found the alternative described above.

Monday, March 17, 2014

Miscellaneous Monday quickies: volume adjustment via keyboard

Being an enthusiast of minimalist GUI systems, I'd heard some time ago of the i3 window manager and liked what I'd read. Recently, I switched over a couple of my computers to it and have been quite happy with it.

I ran across a news item the other day that was touting the virtues of i3 and which therefore caught my interest. Especially intriguing was the author's description of how, using that WM, certain keyboard keys or key combinations could be mapped so as to govern the computer's sound ouput--intriguing, that is, even apart from the fact that it was a description of a system configured to use pulse audio for sound output (my preference for ALSA over pulse is material for another entry). Still, I felt it should not be too hard to modify those directions to suit my systems.

As in the article referenced, it was a simple matter of modifying ~/.i3/config, adding some lines. In my case, the lines were as follows:



The keyboard on that particular machine is what I believe is called a "multimedia keyboard," meaning that it has a few keys dedicated, rather than to alphanumeric characters, to multimedia functions such as volume control. Finding which key codes to place in that file was a simple matter of using the xev utility. The ALSA--as opposed to pulse audio-- commands for raising, lowering, and muting volume were readily found in an internet search.

After a few trial runs and further tweaks, a quick restart of i3 revealed that things were working as expected. Flush with success from that project, I decided I might get the same thing working on another computer in my apartment--though that computer, since it needs to be usable for my wife, runs a different WM; incidentally, it runs JWM with a home-brewed Gnome 2 mock-up interface (I plan to do a write-up someday describing the Gnome 2 mock-up I created).

The basic idea of getting keyboard keys controlling volume is the same, though it involves editing a different configuration file--named ~/.jwmrc--that uses alternate syntax. Since the keyboard attched to this machine is not a multimedia keybaord, I ended up repurposing some seldom-used keys, in combination with the Alt key, for volume control functions. The entries in that file are as follows:



That pretty much sums it up this quickie entry.

Saturday, March 8, 2014

Miscellaneous Saturday quickies: udev rules and you

PREFACE: "udev is a device manager for the Linux kernel. Primarily, it manages device nodes in /dev. It is the successor of devfs and hotplug, which means that it handles the /dev directory and all user space actions when adding/removing devices, including firmware loading." (Wikipedia entry for udev) Those wanting a better orientation to udev may wish to do some further reading of material found at some of the links provided in this entry.
I felt a great sense of triumph when, oh, 5 or 6 years ago, I managed to create a udev rule that would make a scanner I was trying to use be identified in a certain way to the system. In the wake of that project I was also able to craft some udev rules for some external hard drives I was using. Since then, I've learned, however, that computer tech is a quickly moving target; the things I took such great pains to learn and apply back then, as I now know, might be of little use to me in just a few short years.

Case in point: fast forward to yesterday, when, after a Mythtv/Mythbuntu upgrade, one of the capture cards I'd written a udev rule for was no longer being properly identified to the system. The reason being, of course, that some changes had been made to udev conventions and the old trick I'd used to identify that card to the system was no longer working.

So I had to rewrite the rule. It turns out some parts of the routine for identifying and naming devices have been a bit simplified. The new incantation I needed to run to find out details about the catpure card which I could incorporate into the udev rule goes like this:



(where sdb is replaced by the device name of the hardware you're querying--in my case, video0)

That bit was lifted from a 2009 entry from a blog located here. He references an even older web page as a source for his information, one I'd used in my first attempts 5 or 6 years ago, and which looks to be pretty outdated now. That page is called "recativated" and can be found here.

In any case, an even simpler rendition of the incanation above is offered in the "comments" section of that blog, as follows:



Both gave the results I needed and helped me resolve the issue of the card being identified and labelled as I wanted it to be. Maybe this information will be useful to you as well--at least so long as you find and try to apply it before the next big change comes to udev, or udev gets superseeded by some other, "better" utility.

Wednesday, November 27, 2013

14th installment: home-brewed WOD by e-mail daily

I used to subscribe to an on-line dictionary's word-of-the-day (WOD) program. That entailed signing up, using a valid e-mail address, on their web site so that they would, each day, send a different WOD along with its definition to that address. The service proved to be a bit flaky, however, and the e-mails would sometimes get caught up in my spam filter. So, somewhere along the line--perhaps owing to an e-mail address change--I stopped receiving those educational e-mails.

I'd had in the back of my mind going back to using that service but hadn't signed up again--all the while having a nagging suspicion that it must be possible, using open source tools, to cobble together some way of doing this sort of thing from my own computer, thereby obviating the need to sign up for some service. But could I, with my modest technical acumen, actually pull this off? Read on to find out the result.

Meantime, as I've continued learning my way around GNU/Linux and computing in general, I made some headway in learning how to use the program remind to help me keep track of scheduled appointments and to-do items, even progressing so far as puzzling out how to get my computer to e-mail me my schedule on a regular basis. Perhaps I'll write more about that accomplishment--of which I'm quite proud--in a future entry.

The relevance of that observation to the present post is that I learned how to use the program mail, along with the small msmtp, for sending--when triggered by cron--to myself automated reminder e-mails from my system. So some major ingredients were actually already in place that would allow me finally to implement my own, home-brewed WOD-by-e-mail solution.

This was perhaps the final piece of the puzzle for me, although another crucial piece had been under my nose recently as well, something I ran across while investigating bash functions (I wrote about that a few installments earlier, as you can see here). By adapting one of the bash functions I'd found, I was first able to see the WOD from the command line by simply issuing wod from a command prompt. But I soon began forgetting to do that, which spurred me to consider once again having the WOD somehow e-mailed to me.

Finally, putting two and two together, I realized I could adapt the thrust of that function to my needs by having its output placed into the body of an e-mail that would be automatically sent to me each day at 6 A.M. Following is a description of how I did that.

A key ingredient I have not yet mentioned is the text-mode browser lynx, which produces an html file that gets parsed for material that will be inserted into the e-mail body: and I didn't mention it because lynx and me go back a long, long ways--clear back to the close of the twentieth century, to be precise. The line, swiped straight from the bash function I found on the web, is as follows: lynx -dump http://www.wordthink.com/. That simply "dumps the formatted output of the default document or those specified on the command line to standard output," as the man page tells us--obviously not enough to get a WOD into an e-mail body, but fairly close.

What's needed, then, is, like the bash function, to pipe that output through grep, searching for a certain pattern, then to extract from it the relevant lines which belong in the body of the e-mail. Those results then get piped to mail, which inserts the lines into the body of an e-mail. Below is the full line that I inserted into my crontab file, minus the bit that tells the line to be executed at 6 A.M. daily:

lynx -dump -nonumbers "http://www.wordthink.com/" | grep -A 10 -m 1 "Today's Word of the Day" | mail -s WOD my-addy@my-mail.com

This cron entry tells lynx to dump the page found at the specified link to standard output (whatever that means), then to pipe that through grep, searching for the phrase "Today's Word of the Day." Once that phrase is found, grep is to stop searching (the -m 1 switch--it's to look for only one instance) and to "print" the ten lines preceding (the -A 10 switch), which actually then get piped to mail and become the body of the message. The -s switch specifies what the subject line of the e-mail should be. The -nonumbers switch just tells lynx not to preface the links it finds in the page with numerals between square brackets, which it would otherwise do.

That's about it for this entry. I really do need to write up a remind entry, since I had hoped long and hard to find some scheduling utility that would be no-frills, yet powerful enough to issue me reminders on a regular basis. So that may be next on the agenda for this blog.

Some afterthoughts: piping the output of lynx -dump through grep to extract target text is not ideal, since--if I've read its man page correctly--you are limited to extracting text by line. A problem arises here because the number of lines for the target entries for the WOD can vary day-by-day. As a result, it is likely that either extraneous line(s) will be included on many days, or that some target line(s) will get cut off on other days. Perhaps piping the lynx -dump output through sed or awk--which, as I understand it are both far more flexible when it comes to identifying target text--might be a better solution. But because I am not well-versed in either of those utilities and because extracting the WOD from web sites whose layout may change at any time is a moving target, I am presently not attempting to improve on the method I've described here. I do, on the other hand, welcome suggestions for improving this WOD-by-e-mail solution from any reader who may know those--grep included--or other utilities better than I.

Thursday, November 14, 2013

13th installment: how slow is too slow for a motion detection security cam system?

In this post, I'll answer a question to which I hoped I'd find an answer on the internet--but I did not manage to find that answer. The question is about minimal specs for a motion-capture machine and, though my answer will have to remain somewhat imprecise owing to the fact that I did not test multiple systems, it will at least give a probable base-line for what may be the lowest-powered system one could use for the task I'm describing.

So, without further ado, on to a description of the task. Or, more specifically, I'll start off describing what precipitated the task.

For some months now, things located in public areas of the apartment building where I live--for example in the corridors or the garage--have been disappearing. I assumed it was only affecting others until I noticed that a cheap DVD player I'd put in the exercise facility here had disappeared. Then, I noticed that certain bicycle parts and tools had vanished from my garage space.

I decided I could take at least some action toward stemming the theft and perhaps catching the perpetrator, by setting up a security camera. I knew that GNU/Linux had utilities for recording from motion detection cameras, and some preliminary searching revealed that the motion program was likely to suit my needs.

It so happened that a friend had recently passed along to me a decent webcam, so all I needed to do was find a target machine on which to set up the software. An old laptop would have been ideal because of the small size, but I didn't have one available.

What I did have was an old all-in-one unit, an early LCD monitor with a built-in computer--in the person of a laptop motherboard--in its base. I even had Debian (Squeeze) already installed on that machine, since I'd set it up for my father-in-law to use when he visits. But I'd taken the machine out of service a couple of years ago, judging that, as a single-core machine with a 433 MHz Celeron and 192 megabytes of RAM, it was getting a little long in the tooth to be useful anymore. So, could this ancient machine actually be used for a motion detection security camera?

I won't in this post go into the particulars of setting up motion, which did not prove particularly challenging. But after stripping down the operating system to the basics, installing motion, and editing its configuration file for my set-up, I was able to get it to run and record on this machine.

Though the web-cam is capable of 720p recording, I had to settle for 640x480, since the older USB 1.1 ports on this machine could not handle anything approaching the bandwidth high-definition video demands. And the hard disk on this machine, at a measly 6 gigabytes, was not a good candidate for recording HD video anyway.

Once I'd disabled, per the motion documentation, alsa's snd-usb-audio module, I was off to the races with this rig. I did manage to find an 40 gigabyte hard drive for sale for $3 which, when added, upped my recording capability from about 2 months to a little over one year.

So, in case you're wondering, as of this date (late 2013), you can actually run a single* motion-sensing camera, if you're satisfied with VGA video quality and a low frame rate (I've set it to 2 per second), on a single-core 433 Celeron with as little as 192 megabytes of RAM. It will even happily run ffmpeg and stitch together the stills it captures into a video for you.

* I didn't try but am virtually certain such a machine could not handle two cameras.

Wednesday, October 30, 2013

12th installment: adding watermarks to documents

In this twelfth installment, I'll describe my recent success with adding watermarks to a document. As often happens when I want to do a quick document or need to work on a .doc file, I turned to LibreOffice for this task. The major part of this post, then, will be occupied with how to add watermarks to documents created in or edited with LibreOffice/OpenOffice. I decided, just out of curiosity, to look into how watermarks can be added to TeX/LaTeX documents as well, so I'll share as well a bit of information that I gleaned about that from another site.

First, though, a bit about watermarks. As the wikipedia article on the topic tells us "[a] watermark is a recognizable image or pattern in paper that appears as various shades of lightness/darkness when viewed by transmitted light (or when viewed by reflected light, atop a dark background), caused by thickness or density variations in the paper."

Watermarks proper are actually added into the paper itself during manufacture, and the text was later printed over the watermark. With the advent of modern computer printing, however, it has become possible to print "watermarks"--actually it might be better to refer to these as pseudo-watermarks--onto standard, clean paper and so to add them, page by page, to a document. This is the sort of watermarking I will be discussing.

This pseudo-watermarking might be added to a document for a number of reasons: a background image--such as a business logo--might be wanted in a document; a copyright notice might be added to a document in this way; or a document might need to be identified as a draft, as opposed to a final revision. The latter of these scenarios applied to me and was why I wanted to learn how to do pseudo-watermarking.

I was pretty certain I could readily find instructions for how this is done using LibreOffice, and a quick search proved my supposition correct. That search furthermore proved that it is a fairly trivial task, so long as one feels comfortable with using some image editing or creating software. I used GIMP for creating my image, though I decided as well to experiment with LibreOffice Draw and had success with it as well. The image created is simply selected as a background for the document. The steps I used were as follows.

First, open GIMP and select File > New. In the resulting dialog, I changed the increments for image size to inches, so as to create an image that will fit within an 8.5x11 inch sheet.

Once I'd selected the size I wanted and created the file, I next went to the GIMP toolbar and selected the Text Tool. I printed in the resulting window the text I wanted to appear, selected a light gray color for the font, changed the font increment to point, then increased the font size substantially (as you'll see in the screenshot, I went with 213 point type).
The somewhat tricky part after having done that was to rotate the text such that it would run across the page at an angle. This I accomplished by selecting Layer > Transform > Arbitrary Rotation. Doing this raises a window with a slider that allows you to rotate the image to the desired angle--in my case -57.66 degrees. As will be evident in the screenshot, the text can be better centered in the image using this dialog as well (x and y axes).

Thus, the final product (not very well centered here):
I exported that image to a .png file as the final step. From here, it's a simple matter of opening your LibreOffice document and clicking on Format > Page, selecting the "Background" tab, selecting "Graphic" from the "As" drop-down menu, and finding and selecting the file you just created using GIMP. Once that's done, all pages in that file will have a pseudo-watermark with the text "Draft" on them.

The initial video I found described making the watermark using LibreOffice's Draw program, so I decided I should have a try with it as well. That process was almost as simple as GIMP's, but it had the limitation that the largest font size I could select was 96 point--a bit on the small side. I will nonetheless outline the steps here.

First, I opened up Draw and selected the "T" (for text insertion) from the toolbar at the bottom of the page.
Next, I selected a light gray font color and the largest possible font size from the menu, and printed the text "Draft" in the page. The text ends up being in a horizontal orientation, of course, as can be seen in the screenshot.
In order to make the text run at an angle across the page, it is next necessary to choose the "Effects" tool from the bottom toolbar (the symbol has two blue boxes off kilter from one another and is situated fourth from the right side on my toolbar). Once that's done the highlights of the text box just created turn red, and if the cursor is moved over the top right corner of that text box, the box can be dragged such that it is oriented on the page at the desired angle.
Once the text box is satisfactorily oriented and centered, the file can be exported. Once again, I chose the .png format. The resulting image can then be added to the background of a document using the same process followed above to add the GIMP image.

Finally, though I did not try out this last method, I wanted to see how difficult or easy it might be, using TeX/LaTex, to add a pseudo-watermark to a document. I easily found some directions here. That author describes three different methods, the simplest of which--since it is one on which pdflatex can be run directly, is quite easy with use of the graphicx, eso-pic, and type1cm packages, as demonstrated in the code below:


Here's how the resulting page looks:


That's it for this installment.