Archive for ‘Reference’ Category
Browse:
Reference »
Subcategories:

Title says it all…..head over to TechPosters (kinda slow right now) and snag your favourite cheat sheet/reference card. There are also more of this kinda stuff over at Cheat-Sheets.org as well.

Recuva: Free Recovery software for Windows….

datePosted on 13:43, May 6th, 2009 by Many Ayromlou

Lost a couple of files today by mistake (that’s what I get for using Synergy keyboard/mouse sharing application to run in windows)…..anyways, after a bit of googling I came across a very nice and simple recovery tool….Recuva. This one even recovers stuff that’s been deleted from the Recycle Bin (which was my case/mistake). Nice….and did I mention free :-).

JetBytes: On-the-fly file transfer……

datePosted on 10:19, March 24th, 2009 by Many Ayromlou

Neat idea…..You all know about sites where you can upload a large file, for your friends to download. It’s simple, but what if you don’t want to store the file somewhere. It suddenly gets a bit harder, right. Now you need to bring up that FTP/SSH server, create userid’s, open firewall, forward ports, etc. You get the idea.

Well, that’s were Jetbytes fits in. It’s a simple on-the-fly file transfer web service. You go to their website, choose the file you want to pass on to your friend. The site prints out a temporary/random URL, you send your friend the URL and as long as you stay on the page, they can download the file by simply clicking on the URL.

JetBytes does nothing more than route the file through their web server, allowing you to share large files easily with others even if one or both of you are behind firewalls. There is no restriction on the size or type of the files. Oh and did I mention, JetBytes is a free service.

RevoLabs makes Microphones cool again….

datePosted on 21:53, March 28th, 2008 by Many Ayromlou

A friend passed this on today (thanks Jeremy). If you use a mic in your day to day businness (or even if you’re an occasional ichat/skype user, you should check this out. RevoLabs have introduced a new line of Wireless microphones that come with RF-Armor. What does that mean, well the next time your GSM phone rings/sync/receives email, your microphone won’t be going all crazy. Plus their Solo mics come in three different types:

  • Wearable
  • Tabletop Boundry
  • XLR adapter for handheld mics


All their mics use a base station that hooks up to your PC or Mac via USB (no driver needed) and show up as a sound device. As a bonus the wearable one also has a audio out so you can wear it around your neck (on in your pocket) and hook up a headset to it as well.
They also have larger 4 channel and 8 channel wireless systems that you can mix and match using different solo mics. The preconfigured systems even come with a 4 or 8 channel Gentner echo cancellation device by polycom. Very nice…..

Computer History Museum on YouTube

datePosted on 12:19, December 17th, 2007 by Many Ayromlou

If you like to see some of the most prolific Engineers and Scientists of our time talk about how we got to where we are in computers, head over to the Computer History Museum Channel on You Tube. Oh, and if you’re ever in Northern California somewhere, take a side trip to Mountain View and visit the Museum in person, I did.

Okay so this all started with our users not being able to share files on our webserver. We use SSH only for upload/download and interactive access (ie: no ftp). Through trial and error we found out that the default umask (under OSX Server) for sftp uploaded files are 0033 (ie: rwxr–r–) and directories are 0022 (ie: rwxr-xr-x). This creates a problem when one user uploads a file and another user downloads/modifies and tries to re-upload it — they simply can’t because the group permissions are wrong.

If we were using ftp (which we are not) there are some solutions on the net that allow you to modify the startup parameters for the ftp server so that the default umask for all files is 0013 — which would allow a group of people to share/overwrite each others files — but we are using ssh only.

So we came up with two other solutions — a shared upload account and/or a cron job that would modify the group permissions on the website directory to allow group sharing. We went with the second solution and that’s where I ran into so many problems that I decided to create this post. You see normally Unix users know that spaces (and strange characters) in filenames are a no-no. Well that’s not true for Windows and Mac users, they use spaces and other odd characters in their filenames/folders all the time.

I started writing — what I thought was — a simple “for loop” script to go through the website folder and change the group permissions. Of course on the first try things didn’t work nicely because of spaces, so I started compensating for that and came up with:
for i in `find /Path/to/www -type d -print0 |xargs -0 -n 1`
This kinda worked, but the for loop would still split the lines when it hit spaces in filenames. I tried to mess around with it and gave up. After RTFMing a bit more I tried:
for i in `find /Path/to/www -type d -exec echo \"{}\" \;`
The thinking behind this was that the exec would echo the filenames quoted and it should work….well it didn’t, the for loop still split the input lines at spaces.

Finally after a latenight RTFM session (and lots of cursing), I think I’ve found the ultimate file handling loop statement:
find /Path/to/www -type d ! -perm -g=wx -print0 | while IFS= read -rd $'\0' filename
Okay so this version uses “while” rather than “for” but it works like a charm and chews through spaces and all other kinds of weird chars and creates a output stream that’s ready to be used by your choice of commands (chmod in my case).

After trimming and optimizing the script a bit, here is the final product:
# The following find will search for
# all files under /Path/to/www, that
# are NOT symlinks, and do NOT have
# group write permission. The list is
# "\0" seperated and the while portion
# will loop around this character and
# ignore everything else in the path.
find /Path/to/www ! -type l ! -perm -g=w -print0 | while IFS= read -rd $'\0' filename
do
# We've found a directory with no group
# write permission, so fix it.
if [ -d "$filename" ]then
chmod g+rwx "$filename"
# echo Directory changed
stat -l "$filename"
fi
# We've found a file with no group
# write permission, so fix it.
if [ -f "$filename" ]then
chmod g+rw "$filename"
# echo File changed
stat -l "$filename"
fi
done

Hopefully you’ll find this code (or portions of it) useful for your own day-to-day hack-and-slash solutions to annoying problems. Let me know if you come up with an even better solution :-)

SONET and Telecomm buzzwords explained….

datePosted on 23:28, September 26th, 2007 by Many Ayromlou

So this is just a short tutorial, so I don’t have to repeat this to every person who asks about the difference between T and E circuits. Here is the whole thing (more or less), (hopefully) once and for all.

It all starts with the Nyquist’s Theorem and Pulse Code Modulation. PCM is the way telephones digitize audio (your voice). Nyquist’s Theorem (named after Harry Nyquist) says that “When sampling a signal, the sampling frequency must be greater than twice the bandwidth of the input signal in order to be able to reconstruct the original perfectly from the sampled version”. Another way of putting this is that to accuretly encode an analog signal (your voice) you have to sample it twice as often as the total bandwidth you wish to reproduce (your voice on the other side).

Now the phone system carries frequencies between 300-4000 Hz, so according to Nyquist, a sampling of 8000 samples per second will be enough to reproduce any frequency within the bandwidth of an analog phone.

Now fast forward past a bunch of engineering mombo-jumbo (keeping the 8000 samples/sec in mind) and we get to DS-0, the magic designation of the foundation of digital communications. You see the standard way of to digitize a phone call is to record (transmit) an 8-bit sample 8000 times/sec. This PCM encoded stream requires a bandwidth of 64,000 bps. This 64-kbps channel is known as DS-0 and is the foundation of all digital telecommunication circuits.

So now that we have our base unit (DS-0) lets look at one level higher, the T-carrier circuits. You’ve probably heard of a T-1 line, right? Well a T-1 line is actually 24 DS-0 lines multiplexed into a 1.54 Mbps line. The proper definition of a T-1 line is actually DS-1. Now for your trivia question…..what’s a E-1? Well it’s similar in concept to a T-1 except the Europeans actually used 32 DS-0s to define E-1 (rather than 24 like in North America). BTW the really confusing part is that an E-1 — despite having 32 channels rather than 24 — is also called DS-1…..go figure.
Usually T-3 is the max and it’s pretty uncommon to find higher T-carrier circuits (ie: T-4, 5’s). That’s where Optical Carriers (aka OC) come in. The SONET (Synchronous Optical Networks) were developed to push the T-carrier systems to the next level (ie: Fiber). SONETs are based on the bandwidth of a T-3 line (44.736). Actually the are exactly 51.84 Mbps, the difference being attributed to overhead. This is what they call OC-1 or STS-1 which is the basic unit of measure here.
So now you know all there is to know about the telecomm buzzwords, but please keep in mind that the industry is changing and as we speak Dense Wave Division Multiplexing (DWDM) schemes are jepourdising the future of the above technologies (anyone remember ATM?)

Make your browser faster (safer) with OpenDNS

datePosted on 14:49, September 9th, 2007 by Many Ayromlou

Okay, so this worked for me. I don’t promise that it will do the same for you. Let me explain, my ISP (who shall remain nameless) is very good (good uptime, unlimited, good throughput), but for some reason has horrible DNS servers. I normally try not to use their servers and instead use either my own from work or the University’s upstream provider servers. They are okay, but not blazing. Recently I was told about OpenDNS and I meant to look at it sooner, but didn’t, until the servers I was pointing to went down last night. Well, I have to admit, aside from being safer (because they filter fishing sites at DNS level), OpenDNS kicks butt. It is fast as hell and seems to even have enough smarts to remember mistyped addresses and resolve them properly.

Setting it up is real easy….Just go to OpenDNS.com and change your OS’s DNS field to the ones they advertise on the right side of the screen. There is also step-by-step instructions for all OSes as well. Personally I just changed my DSL routers DNS fields and am now racing through websites. Amazing what difference a responsive DNS server can make to your browsing. Obviously your milage may vary, but generally I have only heard good things about their service.

Computer Monitor Calibration….online!!!

datePosted on 14:06, September 9th, 2007 by Many Ayromlou


I came across these two sites last friday while trying to setup a projector. If you’re stuck in the field and need to get a monitor/projector calibrated fairly quick these two sites are for you. First is displaycalibration.com which has been around for a while. It’s simple and works well for setting up your devices contrast/brightness settings and doing simple colour setup. The second site is tft.vanity.dk. These guys are pro’s when it comes to tools for LCD setup. They do the standard contrast/brightness stuff (using a very cool flash app may I add). On top of that they do ghosting tests and colour bleed tests (using their flash app). This could be really useful if you want to compare a couple of monitors in the store or if you want to see how well your monitor is performing. Make sure when using the flash apps that you check out the “Menu panel” that pops up when you move your mouse to the top of the screen.

Google Earth does the Skies….

datePosted on 05:44, August 23rd, 2007 by Many Ayromlou

Google has just announced google earth 4.2 and new to this version is the Skies. Several Sky layers are listed on the left-hand side, including Constellations, Backyard Astronomy, Hubble Showcase, The Moon, The Planets, User’s Guide to Galaxies and Life of a Star. The Sky layers are composed of over 1 million photographs from various scientific and academic sources.

Another new feature in Google Earth is the addition of super-high resolution photo content, which you can see by adding the layer Primary Database -> Featured Content -> Gigapxl Photos. Unlike Google Street View, these photos however are only available for a few select places (like buildings), so there’s not a lot of random fun stuff to be found.

So go download your free copy, install and hit “Switch between sky and earth”. This is absolutely fantastic and serves as a great resource for research and education. Thanks Google….You guys ROCK!!!

12Next