Evanescent Thoughts

You might wanna check this to get a context of what this post is about. With the previous versions of flash, I could get a copy of the videos being played in my browser by taking it from the /tmp directory. But with the new flash player, it deletes the file from /tmp after creating it. Why ?? I seriously have no <insert blasphemy > idea !!. Generally when your browser plays a video using flash player, a process would be fetching the video from the internet, storing it in /tmp directory with a hashed value and the browser tab would be playing it. But now, we need to get around a lot of shit, just to copy your favorite videos. You may ask me why am I so bothered to do this. Answer is that, I generally stream the videos when I have an ultra fast net connection(which doesn’t happen to be my home), store them in my comp and then later watch it on vlc. You might also use some youtube-dl or other addon…. But those generally work only with youtube. Say you had a video which was directly uploaded on facebook or other website, I am not sure if you can copy that. Enough of trying to convince you, that this is actually something interesting !! Lets get to the problem.

First, we may assume that the video was never saved on the disk. But who would be insane enough to put videos that size to MBs in your main memory ?? So it has to be on the disk somewhere. When the video is being deleted from the /tmp directory, it doesn’t mean that its actually deleted. Lets take a small de-tour to the OS basics. When two or more processes access the same file, they all get a file descriptor and when one process deletes the file, it doesn’t actually get deleted unless all the other process close their own access through their file-descriptor. And here, we have a process which is buffering the video into the disk and later deletes the file from /tmp and another process ( your browser tab) which is still playing the file. And voila !! We can still recover the video. Now this is no black magic !! You can see countless articles online about how to recover deleted files which are still open by some other process ( I think I have an a post on that somewhere in my blog too). But what complicates the things ??

Browsers nowadays run each tab as a separate process. So identifying how to access the file descriptors of the particular tab playing the video is the first concern.
I generally stream multiple videos. So I sort of need to write a script that finds all deleted video files from /tmp and copy them back.

How to do this ??

Get the PID of all the tabs of your browser, in my case chromium (Google chrome’s momma).
List the open files of all the PIDs we got from above and see if any of them have a link to a deleted file, specifically in /tmp
Process the output of lsof which also gives the file descriptor.

Here is a run through

sathya@Phoenix:~$ pgrep chromium
2366
2449
2451
2696
2700
2702
2710
2719
2744
2764
4506
4515
4993
5039
5125

Now list the open files of all these process by appending them into a comma separated and grep them for deleted files with /tmp/Fl*. Assume for now that $PIDS has all the PIDs of the tabs with video open.

sathya@Phoenix:~$ lsof -np $PIDS | grep deleted | grep /tmp/Fl*
chromium- 4506 sathya   25r      REG        8,5 33356235   998384 /tmp/FlashXXK9gZKa (deleted)
chromium- 4506 sathya   32r      REG        8,5 10544205   998386 /tmp/FlashXXO0GYZw (deleted)

Now the column 2 gives the PID of the tab and the column 4 gives the file descriptor. I have opened both the videos from the same tab and hence the PIDs are same. Now , the 4th column gives the file descriptor followed by the permission (which in this case is r (read)). Now how to get to this fd ?? The /proc exposes the RAM which has all info about the processes to the user and we can get to the file using the file descriptor from there.

sathya@Phoenix:~$ cp /proc/4506/fd/25 ~/Desktop/GotItMF.flv

There !! We have the video file !! Now all we need to do is, put all this together in a script, which I did.

for i in `pgrep chromium`
do
     PIDS=${PIDS}$i","
done
PIDS=`echo ${PIDS:0:${#PIDS}-1}`
export IFS=""
for i in `lsof -np $PIDS | grep deleted | grep /tmp/Fl*`
do
     PID=`echo $i | cut -d " " -f 2`
     FD=`echo $i | cut -d " " -f 6`
     FD=`echo ${FD:0:${#FD}-1}`
     cp /proc/$PID/fd/$FD ~/Desktop/$PID_$FD.flvdone
export IFS=" "

If you are too scared about meddling with the IFS, use the following which does some clever awk scripting.

for i in `pgrep chromium`
do
     PID=${PID}$i","
done
PID=`echo ${PID:0:${#PID}-1}`
lsof -np $PID | grep deleted | grep /tmp/Fl* | awk '{gsub(/[a-z]*/, "" ,$4)} { system("cp /proc/" $2 "/fd/" $4 " ~/Desktop/" $2 "_" $4 ".flv") } {print "Copied "$2"_"$4".flv"}'

Thanks to Hari for making me revisit bash strings and Jai for the AWKgasm !!

UPDATE : As Rik pointed out in comments, lsof with -n is much faster since a lot of time is wasted in host name lookup (which we obviously dont care abt).. -n makes it not convert the addresses to hostname. Makes it 10X faster !!

UPDATE : I recently switched back to firefox and to make it work on firefox, change the “pgrep chromium” to “pgrep -f libflashplayer.so”

Written by Sathya Narayanan

February 15, 2011 at 10:23 pm

Posted in College life, computers, general, Linux

The Indian Scenario

with 11 comments

The following is a random premature thought of what in my opinion is going wrong in India, which I am sure a lot of people think about. Well I am not gonna put on the Raja Ram Mohan Roy costume and lecture about changing the society and stuff , but I do feel that filling up a few bytes on the internet about this isn’t a very bad idea either.

So, Whats wrong with India ??? I mean we are a body of 1.2 billion people constituting 20% of the world population. Which means out of every 10 guys on this planet, 2 of them are from India and 2 are from China and the rest 193 nations of the world constitute the remaining 6. Yet we just have nine Noble Laureates, and three of them are of foreign Origin. When we are 1/5 th of world population, no matter how screwed up you were with your 10th grade probability calculations, its not a tough job to figure out that Indians must be in top of everything.. not just population. But why is it that, when u take any field, its tough to find an Indian doing better at it ?? I am not talking just about Academia or Research for which every Indian’s instant response is the two worded phenomenon – “Brain Drain”. Lets talk about sports.. How tough is to find a runner who can at least fetch a bronze medal in Olympics. Why is it that when we have Hockey as our national game, a majority of Indian kids don’t even know the names of the players(not like I know any of them). But every one does know that Sachin Tendulkar did start playing cricket at the age of 16 and has blah blah runs in his pocket and runs a restaurant in Mumbai. If we are so obsessed with cricket, why don’t we bloody change our national sport to Cricket !!!. Whats stopping us from doing that. Oh wait !! we are a democratic nation run by a bunch of corrupt politicians who roam around like zombies in wheel chair.

Population :

Population IS THE biggest feature of India. As a strength, it gives us diversity. You can go all around the US and you will pretty much get bored of the same burger and pizza and the food varieties and culture it throws at you. Now back in India, you walk a few kilometers out of your district, you might actually end up in a totally different culture.. A different sect of people who talk a different language, who listen to a different music, eat different food, have a whole array of local cinemas and cine-stars.

I sometimes get curious as to how India ended up with such a big population. I mean how ?? May be the so called Gods had such a plan you know, to stuff maximum number of people into this country and to top it , they had to make the whole country HOT and TROPICAL that when Mr Software-Engineer returns from work in the evening, he has to deal with both the HUGE traffic and import supernatural powers to tackle the hot weather outside. At the end of the day, all that is on top of anyone’s mind is how to survive in this place. At times we even manage to have entertainment amidst all this and that’s why people all over the world respect Indians. They can almost survive any bullshit thrown at them. They are cheap labor who don’t mind sweating it out because compared to what they were doing back at home, anything that you throw at them sounds like luxury.

If India has a 1 billion population, it also has an equal number of divine supernatural entities aka God. At times, you even wonder if they count the number of Gods into the population stats. And Sachin Tendulkar does contribute under both the human and divine category to the population stats. How are you even supposed to survive in a country with so much population??. On one side, having a diverse population is a positive thing. But what actually happens in India is a different story. Lets do a simple math. Say X guys were supposed to live under a km-square of area and it takes Y units of money to provide all necessary amenities to that area. Doesn’t it make sense that with the X very high in India, it would actually be easier to develop infrastructure and facilities ?? No .. that doesn’t happen because, One – we don’t pay our taxes properly. We just love painting our money black. And two – we cause more damage to infrastructure than the amount we contribute to build that. And the moment we step into a foreign nation, we don’t spit, we don’t urinate in public. We suddenly get a public sense of responsibility. We enforce that because every one else around you does so. In India, if you don’t cause any public nuisance, you get a nice portrait of yourself in the “Hall of Clowns who follow rules”. And nobody wants to change. We just continue living our lives putting up with all of the crap happening around us and contribute to it.

The Indian Rat Race at Schools :

Lets get back to where all the talented people in India go to ??. The first thing that you notice is, every body in India wants a shortcut to success. By success we mean making more black money. How many of us actually think about living the life on our own ??. Half the Indian kids grow up listening to their parents. The parents mold their kids into who they wanted to be when they were once in their childhood. Its a sort of a pipeline where your dad wants you live his dream and you want your kids to live your dream. You just throw your dreams onto your kids. “Here kiddo, take all this books and digest them and become a doctor., Because, I once wanted to be a doctor and I didn’t have facilities back in my childhood to achieve that. And this will also make you rich and powerful in the society”. I agree on the fact that parents have the responsibility to teach their kids of how to become successful. But going a step further and choosing how they do it and in what field they do it is an over kill. And hence every kid gets lectured to be an engineer or a doctor. No one advices their kids or even talks to them about other areas like sports, literature, science, history, economics, politics, art etc. Those fields are for kids who missed writing their 12th std board exams or those who forgot to bring a pencil to exam hall and lost out on marks because they didn’t manage to underline the important points in their answers.

I feel like kids of this age are stereotyped into doing things. Each mom compares her kid with the other kids in the neighborhood and lectures him/her about how they need to take them as role models and score better marks in the next exam. And thus the rat race of engineers begins with a big fat salary cheque on the other end. So most of the kids never get to explore the opportunities in the other fields. A lot of talent actually comes out in this Rat Race. Thats why when you go abroad and see a graduate student struggling with calculus, you just realize how great the Indian Schooling was. But most of these kids who could do calculus by just hand waving, don’t actually end up as successful engineers compared to what US produces as undergrads and graduates. Thats just because once the Rat Race is over, we all take a well deserved rest during our undergraduate period. In the contrary, students abroad have a steep learning curve during Undergrad and graduate courses. Which just doesnt happen in India. Thats why even though we have a very successful schooling system, we have a very bad undergraduate experience ( IITs in my opinion can be exempt). There are several perspectives to this but lets rest on this.

Why Brain Drain??

So we only manufacture engineers in our country and what happens next ?? All these bright engineers run away to better places in the world because, those not-so-talented kids who chose the other important fields that constitute a society, do a bad job in their field and make the place a hell to live. To become a developed nation, India doesn’t need top notch computer scientists, but it needs talented people in the other fields who make India a better place to live. You need a good politician, a good economist a good city planner, so on. But no one wants to choose these because they are poorly paid or have no clear shot at success in Indian terms and scenarios. So why not give these guys who do the less interesting but important jobs a better future. Lets lure the talented people into these fields. One of my batch mates who graduated with an Instrumentation & Control Engg degree, decided that Politics was the field he wants to be after he joined a company for work. He even went on to enroll for some correspondence courses in politics as he works. Now if some one had put a thought in him when he was a kid that a politician was some one whom the society respects and needs, he wouldn’t have wasted 4 years in NIT Trichy attending crappy engineering classes. We would have had a good politician who could have run the CWG without any corruption or not cause $36 Billion loss to Indian government over the spectrum allocation. What India needs is not eradicating brain drain and stopping the talent from going outside the country. But what India needs is to make sure that a fair share of the young talent pool goes on to contribute and develop the other fields that contribute to the society. And of course yeah better politicians.

PS : All of the above are random thoughts feel free to smirk them off if you are not in the mood to listen.

Written by Sathya Narayanan

November 18, 2010 at 12:55 am

Posted in Bugs, College life, computers, general, Rants

One month into the Grad Life !!

with 8 comments

Its been more than a month into the Graduate Life at Univ of Wisconsin Madison for me. The first thing I felt missing from my Indian life is Time. Back in India, at times, I was pretty much jobless that I would stay up late in the night and discuss some arbit crap with friends on the garnet lawn or watch some TV Series. I actually ended up watching 18 TV series as a part of my Undergraduate Life :P. But once course work started, it was a round robin between Assignments, Cooking, doing groceries and getting used to America !!.

I am not sure if this applies to all other universities in US, but Wisc-Mad needs you to only enroll for 6 credits per semester if you are a TA. Hence my calendar initially was only filled on Tue and Thurs for a couple of hours. And once they let in TA allotments, it all turned out to be messy. I finally managed to squeeze all TA and classwork commitments to just Tuesday, Wednesday, Thursday. So the long weekend starts on the Friday and lasts till my alarm rings on the next Tuesday morning at 8.00am :P. Needless to say, there are assignments to be done or some or the other thing that comes up. Life here is awesome. You have people who are very sweet and polite to you. Doesn’t mean they actually are in real life. Its just the thing that they have a sweet outer-cover. So you walk into the street full of people, you ll end up with a lots of face gestures wishing you a good day. In particular, in one of the invited talks, a guy from west coast mentioned that people in Madison are super sweet.

Fall is beautiful. Just a pleasant thing to watch. I was usually this person in India who rarely manages to step outside the 5m invisible ring around a laptop. But out here, the best thing I like to do is go and sit in front of the lake. Madison has two beautiful lakes and since my university and Madison city are a part and parcel of each other, I am in close proximity to these awesome buildings and places of Madison. The state capitol which looks like a replica of the White House is few minutes walk from my apartment and department. And hence each and every day I go to dept, I feel like I am actually going to work. Doesn’t give you this feeling of you walking inside a campus where every one you see is a student or a person with academic ties.

Couple of funny things I encountered here :

Wanna meet a prof ??, No problem. Just walk in … Wanna have your hair cut ?? get an appointment beforehand and be there on time. And beyond that, most of the saloons have women cutting your hair and they charge you anywhere between 10 to 20 dollars for a simple haircut. Taxes are also to be paid btw :P. And I had to pay 16 dollars (and ideally supposed to have followed the golden-20%-tipping rule) for just ending up in an Identity crisis at the hands of a woman in a span of just few minutes. The lady who cut my hair was actually perplexed when she heard that hair cut at India cost me like 75 cents.
Cycling is a lot of fun. And you have a separate bike-lane here everywhere. The whole city is actually very scenic to cycle.
Ever since I came to US, I have always carried only 5 dollars in my wallet as Cash. And to this date, I still haven’t used it at all.
To all those who sit in India and act like this crazy calculator that converts their friends/spouses/kid’s salary in dollars to INR, you wouldn’t be willing to even buy a small candy if you keep doing that over here before spending.
Temperature plays a see-saw most of the time here. It might happen at times, that you see a clear and sunny sky out there and wanna go for a bike ride. You might still end up biking at 8 degree Celsius. Happened to me. So trust me :P.
You gotta figure out clever ways to get your TV episode if you don’t wanna end up missing it or watching it in a tiny 400×300 pixel in your browser.
People take your word for granted here. If you say you dunno who is responsible for this big chunk of data downloaded from your phone eating up your data plan, they just push you up to a bigger data plan free of cost :P.
Beyond seven, anything is not funny at all. So I stop here 😛

Well there actually are many interesting things to put up here, but all that comes to my mind right now is this Lattice framework for compiler optimization which I cant get a hang of.

Written by Sathya Narayanan

October 4, 2010 at 10:06 am

Posted in College life, computers, Ha Ha Ha, Trips

Finding Invisible Friends and Dynamically Updating Your Status in Google Chat using XMPP Scripts #linux #python #ubuntu

with 24 comments

Read on, only if you Wanna do any of the following :

Update your google Chat status with info dynamically or fetch score from a website and display it every minute in your status msg.
Find invisible friends in your chat list.
Wanna change your status message as soon as some one signs on ?? aka make your own Buddy Pounce.
Wish all your contacts by running a simple prog on important days. Like say, I wrote a script that wished my friends “Happy Friendship Day” when they appeared online 🙂 .
Get a step closer to writing your own back end for an IM client.
Wanna remind someone about something over chat at a particular time or period when you might not be online.
And lots more that your imagination can limit.

Warning : I dont promise that everything in this is right. There might be hell lot of mistakes. Feel free to point them out in the comments 🙂

Being someone who does a lot of IM and chatting, I was more curious about how a web chat works. How is it that you are instantly notified of your friend’s online presence and know when he is about to type something on your chat window. A little more digging and reading a couple of sites on XMPP helped me figure out what I have been wanting to do a long time back in College. What basically you need for having a chat with your friend miles away is an XMPP Server (eXtensible Messaging and Presence Protocol) and an authenticated connection established to it. And of course an IM client (like google talk or pidgin or empathy) unless you wanna write your own command line scripts using some Python API for XMPP.

Firstly, I m not a big fan of gtalk, just cos it doesnt exist for Linux platform and who the hell uses an IM client just for google. An IM client is something that maintains all your chat accounts across various domains that u have a authentication on. An XMPP server listens to your xmpp requests on port 5222 and 5223. To give an idea about how the whole thing happens, imagine an XMPP server with which Alice and Bob have established their authentication. Unlike VOIP, chatting is done with a man in the middle which happens to be the XMPP server. When Alice wants to send a IM(Instant Message) to Bob, Alice sends it to the server and the server sends it to Bob. This sending and receiving is done in the form of XML packets. An XML stream runs between the Server and Alice. A similar stream runs with Server and Bob. Whatever Alice puts on the XML stream is received by the server and the server reads the XML packet and looks at to whom the message is intended for and the server puts an XML packet to Bob’s XML stream and hence Bob receives the message Alice sent :). All this happens each time u type something on ur IM client or change your status. Now this is all about messaging. What about the status notifications and stuff ?? Thats where the presence part of XMPP comes to play. Basically a stanza in the XMPP stream between the server and the client can be etiher a Roster/Message/IQ/Presence. A Roster is used to notify the client about who all are online and registered with the server. A Message as I said above is a stanza that is used to communicate from one client to another through the server. A IQ is Info/Query where in u get specific info about a user. And finally a Presence is used to notify your type of availability to the other users (like busy , dnd , away and put a status). This is the view of the XMPP like how say you might see earth flying from an airplane . Each of these have their own specifications and finer details. For more, if you are interested, google it up .

When google opened a subdomain aka talk.google.com, users (the geeky ones) were able to authenticate and start chatting even before google officially announced that it has actually started an IM service :). This happened back in 2004 when google first started the talk.google.com subdomain. Since then it kept on adding features to it chat client and led to group chat and stuff. But as I see, gtalk is not even close to an IM client. Its specific to google and has very limited capabilities when compared to pidgin or empathy. I am not talking about just using multiple accounts but about stuff that you can do with just your google accout like say control the presence notifications, add a buddy pounce n stuff :). Well I can throw in more info with all my current enthu about xmpp but I ll stop here and break straight to the part of writing cool scripts to do stuff with your google Chat that you cant do with your gtalk 🙂

Stuff that you might need : Python interpretor, xmpppy library for python. If you are in Linux , install python-xmpp and python-dnspython packages and you should be clear to go. If you are on windows, Keep breaking your head 😀

The first script I am gonna show here is how to send a message to a friend. This is how I started it. You might wanna cross check with the documentation here.

import xmpp
import getpass

user="sathya.phoenix"
passwd = getpass.getpass("Enter Password: ")
msg="helloworld"
to="deepblue.ar@gmail.com"

client= xmpp.Client('gmail.com',debug=[])
client.connect(server=('talk.google.com',5223))
client.auth(user,passwd)
client.sendInitPresence()
message = xmpp.Message(to,msg)
message.setAttr('type','chat')
client.send(message)

A quick look should tell you that Lines 1 and 2 import the necessary modules. The getpass module helps you to enter the password like the way you would enter it on a computer. Otherwise, you would have to put it somewhere and expose it (even better ways to do this are welcome in comments). I am declaring the variables in Lines 4,5,6,7. Line 9 , I create a xmpp Client with the parameters. When u specify the debug=[] option, the debug messages dont get thrown at you in the terminal. You connect to the server on port 5223 in Line 10 and authenticate in 11. Line 12 sends a Roster request and Initial Presence notification. You construct a message packet in the Line 12 and set its attributes in Line 13 and send it to server in Line 15 🙂 .

The next one I worked on was a script to dynamically update my status message with something like a clock or a cricket score. I am gonna leave to US on Aug 19th and thought how cool would it be to put a countdown on my status that updates how much time is left every minute(First I set it up every second, but it gets irritating to chat on the other end unless you have a very patient friend 😛 ).

import xmpp
import time
import datetime
import getpass

user="sathya.phoenix"
passwd = getpass.getpass("Enter Password: ")

client= xmpp.Client('gmail.com')
client.connect(server=('talk.google.com',5223))
client.auth(user,passwd)
client.sendInitPresence()

while(1):
	diff = datetime.datetime(2010, 8, 19,4,40,00) - datetime.datetime.today()
	days=str(diff.days)
	hrs=str(diff.seconds/60/60)
	minutes=str(diff.seconds/60 - (diff.seconds/60/60 * 60))
	seconds1=int(hrs)*3600+int(minutes)*60
	seconds= str(-seconds1+(diff.seconds))
	timeleft=days+" Days, "+hrs+" Hours, "+minutes+" Minutes more !!"
	pres=xmpp.Presence(priority=5, show='chat',status= timeleft )
	client.send(pres)
	time.sleep(60)

Lines upto 12 are self explanatory . I then start a while loop and calculate the difference in time from the current time to the time when I ll be boarding my flight. The diff gives back a structured variable with diff in days and seconds. The seconds difference is done mod 86400 (ie no of seconds in a day). So make appropriate calculations to count the days, minutes and hours and seconds left in lines 15-20 and I construct a XML Presence stanza by calling the xmpp.Presence() and send it on to the XMPP server. After this, I pause the loop for 60 seconds in Line 24 to send the next update packet after a minute. You could do something like put up Live cricket scores and stuff here to keep your friends informed or put a horizontally scrolling status msg or whatever that comes to your mind !! 🙂 .

The next script that I have is a script to find invisible friends in gtalk 🙂 . This I find pretty much useful. I used to do the other way around (that is to make myself invisible from pidgin by sending an XMPP req) cos Pidgin’s Inivisible status doesnt work well. I found the info here when I was googling it back in my coll. Basically I put the following XML snippet in my Pidgin’s XMPP console to make myself go invisible.

{{{
<presence>
<priority>5</priority>
</presence>
<presence type="unavailable">
<priority>5</priority>
</presence>
}}}

So I try to do the reverse of this from the Roster I get from the server and that should pretty much give the list of people who are invisible on gTalk :). Which I do in the following python code.

import xmpp
import getpass

user = "sathya.phoenix"
passwd = getpass.getpass("Enter Password: ")
server = "gmail.com"

client=xmpp.Client(server,debug=[])
client.connect(server=('talk.google.com',5223))
client.auth(user,passwd)
client.sendInitPresence(requestRoster=1)

def check(connec, event):
   if event.getType() == 'unavailable':
     print event.getFrom()

client.RegisterHandler('presence', check)

while client.Process(1):
  pass

Lines 1-10 again do the same authenticating and stuff while in Line 11 , instead of just sending the initPresence , we request for a Roster which gives us the status info of all my friends who have registered with the XMPP server. Now here is the magic. Even though you are invisible , your client registers with the XMPP server and sets the status as unavailable which the other Clients detect that and put you under the offline category(those who havent registered). So all we got to do is to check for which of the registered users in the Roster are having a status “unavailable”. Pretty simple thing to break someone’s privacy huh 😉 . So we have a handler to handle the presence notifications in the Roster and display the gmail ids that have status as “unavailable” and have registered with the server. Now only disadvantage is that, if your friend is invi , he sure ends up on this list, but not vice versa. There are a couple more to check for that as well :).

So you could write handlers that can do a lot of stuff for you. Like you can send wishes to all online contacts by calling the client.send() in Line 15 and remove the if statement on Line 14. Or when some buddy of yours comes online , you can change your status message to soemthing else . Guess you can figure all that out by looking at the scripts above and combining them and making suitable modifications. Its all exciting !

PS : Any more cool ideas to do, put them on comments. Will try out 🙂 Also check this out if you wanna insert code snippets in your blog the easy way 🙂

Written by Sathya Narayanan

August 3, 2010 at 11:25 am

Posted in Bugs, College life, computers, general, Linux

The Hyderabad Weekend

with one comment

The last time when I visited my cousins at Hyderabad was sometime around my First year. So I planned a small trip with mom over the weekend and it was one of the most exciting weekends for me after coll ended :). Not to forget the adventurous trip on the way back :P. Things that I did :

Did a lot of shopping with cousins. Thanks to Kalapana and Kavitha akka, now 80% of my shopping work is over. We were right on time for the Sales at Lifestyle at In Orbit. I felt like I really did shop something for the first time in my life (I never did any shopping till I was out of College :P).
Met Srinivas, Abhinav and Mrinal at CCD near Hitec City. Abhinav has become like a hindi film star, mrinal is on race with Ankit to gain weight and Srinivas is all the more fair and handsome 😛 . Had a nice time with them though had to run back home quickly as one of my cousins had to catch a flight to Chennai that evening.
The new airport Ring road is Awesome ! 8 lanes and u can easily go on 140 kmph 🙂
Went for a Rock and Jazz concert at Mariut Convention Center. This was my first concert if u dont count those we had in Coll during Festember and all. Was pure fun and was a pleasure meeting some of my cousin’s close friends :).
Karthik picked me up on the way back at 12 in the night and went to his home :). NR and co were already there and Naga sir arrived early in the morning 😛 .. Tirth too came all the way at 1 in the night and we had a nice chit chat till around 3 in the morning :). Not to forget the Zaveri call and the Hyderabadi briyani at some 2 in the night 🙂
Spent the whole of next day at cousins place. Beautiful house .. .given that my cousin is an Interior Designer herself :). I was always scared of dogs as pets. But I found Deva aka the Lazy Labrador very very friendly. He nibbled me a couple of times and that was it. Such a cute one :).
Went for lunch with family at Mainland China. Went to the same one at Banglore few weeks back with Suren and co and guess what I am back :P. This one in Hyd had a better Chineese ambiance and the food was better too 🙂
Got a Leather jacket on the way back and visited a Harley Davidson Show room. Some day , I shall own one 🙂
Went on a Ride on the New Royal Enfield Classic 500 that Ramesh uncle got . It was so stud !! I always felt that bullets were more appealing to me than bikes(even the racing ones.. earlier on the same day , balu let me drive his R15 ).
Got back on a train and reached Chitoor only to find that I am supposed to cross Andhra border and reach my home through some weird way cos it was a State wide Bandh for Chandrababu Naidu’s Arrest. And this area seemed to be a TDP stronghold and they blocked all roads that led to city outskirts and TN border. Not even Cars were let to passby. Only emergency vehicles and 2 wheelers were allowed to pass. Had to take 2 autos to cross 2 such barricades ( the auto guys were also afraid to go cos they were asked strictly not to take on public transport). Cost me some 350 bucks to cross some 12 kms. On the last barricade at the check post at TN border, nothing worked and the auto guy also gave up. We walked all the way across the border with those heavy shopping bags. Luckily some nice guy gave me and my mom lift on a Hero Honda ( yes !! we had no other option left ). So Triples it was. Me and my mom clinging on to that metallic fixtures on the back so that we dont fall off :P. Some how reached home after some 5 tensed hours 🙂

A great weekend in all … A memorable one too . Thanks to my cousins 🙂

Written by Sathya Narayanan

July 20, 2010 at 9:50 am

Posted in general, Its my life, Trips

My days at Theoretical Comp Sci Lab @ IIT-M (TCS Lab)

with 10 comments

I have been wanting to write this post for a very long time. The reason being simple enough, It changed a lot in my life. When I joined fresh at NIT Trichy and completed my first year, I was more into programming and algorithms. Used to sit in I-Lab and do some of those SPOJ problems( yeah!! when I was in First year, I-Lab was good and it wasn’t filled with gultis watching videos on you tube and orkuting ). At that point of time, I was more interested into getting a Stud job once I complete my college. But now after 4 years at NIT-Trichy, I am dropping an offer to join Cisco and heading for Masters at Univ of Wisconsin Madison. I can attribute all of it to Prof Pandurangan and his TCS Lab 🙂 .

Akhil and myself were on the same boat looking for profs to do project work on back in 4th Sem. I was more inclined to do an internship sort of thing at some startup or some small company but was also looking out on the academic sides. One afternoon, when we were busy spamming the inboxes of many such IIT Profs, Akhil mentioned about Prof Pandurangan and told me how his papers regularly appear in ACM’s Conf. And thats when I started mailing him and was fortunate enough to get his reply. Later he came down to our college( he was in the Board that certifies the Departments for some approval) for an official visit and said he would talk with all those interested in taking up internships at TCS lab. We were greatly amused by the way his lecture just kept us hooked on to the topic. One year into the department, I never felt like I was actually learning something new and exciting until I was attending his lecture(yes!! Mohan was taking a course in both the sems that year :P). And thats when I decided to try out the internship and was very happy when he accepted to host a couple of us at IITM :).

So began the wonderful days at IITM TCS lab. The first time , some 8 of us were working under him and unfortunately he could only let us into the lab and not into the IIT M hostels :). So myself and Akhil stayed in the classrooms of KV School. The School was closed for vacations and we had the whole big black board all for us to scribble. Though technically, I should say we stayed at the Lab for 75% of the time in a day :). TCS Lab was more than what we expected, given the condition of Labs at NITT( the 3rd semester, we didnt even have the labs ready and the next sem, I remember the server crashing most of the time :P) .

This was also when we were being taught what research work is. Until then I had no clue what it was to get a publication, a peer review, do a survey, Proof techniques etc. And a whole new exciting world of things was thrown at me. The first time, I spent my time mostly reading papers and getting to know my area well. Akhil, myself and Bharathwaj(from IITB, a engg physics Student) were assigned to work on Multi Party Computation and Information Theoretic Security. In Research, you get excited when you know that the stuff you are working on is barely a few years old and there is a lot of scope for Research work. Also Prof Pandurangan was taking a summer course on Algorithms and it was a Bliss!!. Till date, I havent enjoyed any class as much as I have enjoyed sitting in his classes :). Unlike other guys from my coll who were working on Provable Security and trying to write a Survey, Prof let us work on a Problem right away :). We had to solve couple of Round Complexities in VSS and most of the day , it would be sitting in the TCS Lab and discussing if this works or that works with Akhil and Bharath(also a bit of chatting online with college friends and visiting the canteen freq :P). Bharathwaj was a step ahead of me and Akhil and always had a clear idea of whats wrong and whats right :). He helped me a lot in figuring out few mistakes too. Whenever, we had a small idea we thought would work, we would run to Arpita and Ashish , who were doing PhD under Prof. Now these two deserve more than a special thanks from me cos, I haven’t seen some one so dedicated as them :). In fact, whenever I consider my self if I have to do a PhD in future, I ll be weighing myself against them to check if I am ready :).

The one thing about TCS Lab is that you can find a lot of interesting people to discuss and chit chat including Prof Pandurangan. He would come around the labs, chatting with each one about his work in progress and crack a joke that would have us all in splits :). He would also tell us what it takes to get a good publication out of students.After a few interactions with him, I was more than convinced to not just stop with B-Tech and get a stud job, but to definitely do a Masters. Back then, the Lab would be full with so many students that people who walk past the corridor, would mistake the place where we keep our foot wear for a shop that sells footwear :P. And some or the other old Student of Prof would visit the lab, not to forget the box of sweets that come with them. We had a tradition in TCS lab that who ever gets sweets for Prof [which according to records, he never touches 😉 ], also gets a box of them for the lab inmates. All this experience with the Lab was something I could never dream of getting at NITT :). I dont think any Prof would comeback at Ten in the night to the lab and have discussions till late midnight at NITT ( many of them dont even come to dept in the day time !).

After our first internship, we were extended the opportunity to continue working in the winter also. Prof was always insistent on making us realize how Research is not a one-summer-outing thing. I still tell my juniors who are onto doing research project the same thing. Don’t think of it as a Summer Project or something you get to do for getting a Certificate. A certificate can get you nothing in my opinion. So I said to myself, that I am not gonna give up unless I get a good publication out of this. Also Aishwarya and Anugrah joined me during the winter and we were looking at a new set of problems, hoping to solve them. By the end of it, I almost got some results and it so happened to be the new year eve. During my 6th sem, I was mostly spending my time writing the paper for submission when one fine day, Arpita and Ashish spotted a flaw in it :). And it rest there until the next summer when I went back to lab.

This time, I was totally working on a diff prob, AMPC. And suddenly one evening, I got an idea for the proof to work around the flaw in my previous result. Finally I had a perfect working one(though it was a very simple solution). And Prof wanted to send it for CANS 09 which had the submission deadline in a week or so. So once again we were off to writing the protocols, changing a lot of stuff from old paper, adding new.. And we had a 23 page paper for a conf that allowed only 18 pages with appendix :P. And this is when Arpita and Ashish clearly demonstrated to us how many papers they have successfully authored. The draft before Arpita and Ashish did the corrections looked so amateurish. We had no idea what point to highlight and what to leave it for the reader to understand himself. Using notations, skipping unwanted statements and proofs… learnt lots from them:). My desktop would have draft_1 draft_2 … and so on :P. We worked till some 2 in the labs. Did a lot of night-outs in lab (never heard of students even using labs outside the lab hours back in NITT). It felt exciting and like a whole diff world to me :). Later in August, we were delighted when the paper got accepted. Should thank Sharmi and Vivek too for all those night outs. We used to go to Basera at 2 in the night after doing all the corrections to paper. At times, Sharmi n Vivek’s 2 yr old son Shvithin would come to lab and play around. Such a delight to watch prof and him talk :).

All this made me transform from a guy who aspired to get into a Stud company back in 3rd Sem to a guy who wanted to go for higher studies by the end of 6th Sem. Ironically, Akhil on the other hand who wanted to end up doing research at the end of coll back then is now heading to join Facebook :). I still have no idea what it would have been if I hadn’t gone down this path but I am sure it would have been less exciting for me :). The admits that I got would never have been possible if not for Prof’s motivation and support:). I owe it all to TCS lab , Prof Pandurangan , and my other friends over there( Its actually a big list 😛 ). Those late night chats, running from TCS Lab – I to TCS Lab – II whenever we have something to discuss with Arpita and Ashish, Prof always trying to kalachify Shriram and Kalai, running to the Staff canteen for tea/cofee/icecream/lunch, the stay at KV school, latex work, Seminars, Prof’s jokes, Treats.. a long list of things I ll be missing when I go to Wisc Mad 🙂

Written by Sathya Narayanan

July 16, 2010 at 10:24 am

Posted in College life, computers, general, Its my life, Research @ IITM

Do IM Clients (Pidgin,Skype et al) Detect Subnets and Avoid wastage of Internet Bandwidth ?? #linux

with 5 comments

I Post this hoping someone would explain to me How stuff works when you make a Video call across Internet. Also, Please correct me wrong if I am wrong anywhere. Now, What I have been thinking in mind is that, When Alice and Bob, sitting in different locations( not in the same subnet) try to have a conversation through some IM protocol, the server acts as a mediator. That is, the server gets the message or data from Alice and sends it to Bob and vice versa. So I assumed the same to be the working scenario in case Alice and Bob happen to be in same Subnet but say try to call each other on skype. I am now beginning to doubt this as I noticed something peculiar as I tried to make some video calls. My observation is that in the case where Alice and Bob are in the same subnet and connected to Internet through a common gateway or one of them acting as gateways.

My setup is as follows : All computers run on Ubuntu Lucid Lynx

BSNL Modem : IP: 192.168.1.1 with a bandwidth of 512 Kbps

Vostro Laptop : Connected to the BSNL Modem via eth0 and running a Wifi network on wlan0( 54Mbps) both of which share the same internet connection( refer this ) eth0: 192.168.1.2 and wlan0: 10.42.43.1

Studio Laptop: Connected to the Wifi connection set up on the Vostro Laptop and has the IP address as wlan0: 10.42.43.10 . So any http request from this goes to the BSNL modem via my Vostro Laptop (10.42.43.1)

With this setup, My Vostro and Studio laptops are in a Subnet and they are connected to the Internet via my Vostro Laptop. Now when I start any file download from Internet or torrents, I get some 80KBps on my eth0 on Vostro and some 60KBps goes to the Studio Laptop via the wireless lan 🙂 .. Now I install skype on both the machines 10.42.43.1 and 10.42.43.10 and create 2 different accounts and make a video call from one account to another . Now I thought the connection on 192.168.1.2 was supposed to handle the traffic for both the comps and forward the packets from internet for 10.42.43.10 from the internet server that hosts the video call. But what actually happens is that there is no traffic to outside the subnet. That is my internet traffic is 0 kbps both incoming and outgoing whereas the communication required for the video calls happen directly between 10.42.43.1 and 10.42.43.10 without a single packet being sent to the outside network (192.168.1.1).

So this is something like when a video call is established on a subnet, it works P2P and not through the server on the internet. CORRECT me if this is wrong. To clearly see .. check the following screen shot.

Now the one on the Left is my 192.168.1.2 on eth0 and 10.42.43.1 on wlan0 . The yellow circled one is the traffic on 10.42.43.X subnet . Notice that while the call is in progress, The connection on 192.168.1.2 which is connected to internet is not even 1KBps . Its in Bytes per sec . This is exactly what I am talking about. The video call works Peer-to-Peer as if it is happening locally and not through some Internet Service. Calls to my friends outside, create traffic on 192.168.1.2 as expected. Only when the calls are within the subnet, everything seems to be and inside business :). Quite interesting is it 🙂 . That means, I dont have to pay for the ISP bandwidth that will be used in all this video calls within a subnet. This is why when I called my friends, the audio and video were poor quality and when I called within the subnet, the clarity was awesome :).

This was the case with video calls on Skype and Pidgin on Ubuntu Lucid Lynx.

Now the following questions :

Is this how its supposed to happen?? So the server hosting the video call doesnt have to receive and deliver data during the call if both Alice and Bob are within same subnet connected to internet ??
Is this the case with only video and audio calls or for anyother protocols ???
What is this thing exactly that makes the pidgin or skype detect that it doesnt have to pass the packets to the internet and just pass it directly to the computer on the subnet . It works as though a direct P2P connection is set up.
Does it happen only with Linux or Windows and Mac too ??

Applications :

Imagine you are in an organization and you have say 10 computers connected in a subnet which is connected to an Internet gateway. Now every one within the subnet can do a video chat using the skype and gmail accounts without even passing a single packet to the outside network . This means the company doesnt waste the internet badnwidth when the calls are made within the subnet .. Some thing like calling from reliance to reliance is free :P.

People who have some ideas about this , please post as comments or let us discuss on IM 🙂

PS : wrote it in a hurry 😛 .. so bear with the formatting 😛

Written by Sathya Narayanan

June 29, 2010 at 9:33 am

Posted in Bugs, College life, computers, Linux, Magic

Ubuntu Lucid Lynx Tweaks

with 17 comments

I bought a new Dell Studio 1588 few days ago. It came with an Intel i5 450M processor, 4GB DDR3 Ram, 500GB SATA @7200rpm, 1GB ATI Raedon Graphic Card, 15″ HighDefinition LCD Display(1080p) with 1920×1080 resolutions and a back lit keyboard and a slot load DVD 🙂 .. A perfect config except that, it shipped with Windows 7 pre-installed. The sales rep refused to even give me the lap without installing Windows sighting that they dont send OS DVD nowadays and the only way to give me the Windows 7 I am entitled for is by installing it in my comp. Fair enough I say, and gladly receive the laptop and start working on Windows for a couple of hours( I couldnt install Linux cos, at that time my modem was in repair and I had to wait) only to find that 15hrs later, Windows screwed up my MBR !! Now on any other day , I would have fixed the MBR with a live CD of ubuntu. But since its brand new and still under the windows cloud, I thought of giving the customer care at Dell a ring to fix it and for the rest of the day, I kept staring at a slow green Progress bar. In the mean time, I finished downloading a whole 2GB HD movie on a 512kbps BSNL connection ( Just to give u an idea of how long the progress bar made me wait 😛 ). Finally I gave up on the windows way of fixing, put my Live CD to use and got done with it in 30 mins. Yet another times when you feel a live CD is like your swiss army knife !

So I finally had my laptop ready for Lucid Lynx and it was just splendid to see Ubuntu in HD screen 😀 .. Loads of UI improvement .. guess they are putting better designers at the helm of the task though a lot needs to be done, especially with nautilus’s usage of space and the Desktop icons alignment. Finally Ubuntu has a Copy To and Move To added to the nautilus 🙂 More on the review of Lucid Lynx later. In a matter of time, I upgraded my kernel, installed the updates, got my graphics card driver installed and copied the backed up data from old laptop. And then the actual problem began 🙂

The one Internet connection and Many Laptop Problem :

I had a BSNL connection for internet access and was comfortably using it on my old vostro laptop. Now that I have 2 laptops and I wanted to use both at same time with internet, I was checking out my options to get it working.

The classic option was to get a router , a wireless one … But I wasnt interested in wasting my cash over it .
IP Masquerading .. Make one comp route the traffic from eth0 ( the ethernet card connected to BSNL modem) to the other comp via a wlan0( Wireless card which had a private network established with my other laptop) … couple of iptable modification and this shud be up and running.. google and you would get sufficient info 🙂
Setting up ssh server and doing the above process without any changes to iptables.. You could try port binding ( ssh -L ) or a SOCKS proxy (ssh -d) to make things work .. but SOCKS proxy, I am not sure how to export the proxy for apt-get to work .. (ideas welcome in comments)
The next to easiest way of setting up a http proxy server on one laptop … I a had used in college was squid .. So I set it up in one of the laptops, changed the necessary ACL settings(access control lists) and http_access and done in a jiffy 🙂
This is the best and simplest way …yet the most _not_so_interesting way .. in short the one click windows way !! (yes even ubuntu is becoming bad !!) While creating the wireless connection, Under the ipv4 settings, put the method as”Shared to Other Computers”. This has to be done on the host laptop connected to the internet modem . A very simple one click mechanism .. Think its there in windows too .

Any other interesting ways to do the same, please mention in comments 🙂 … Also note that to do all of the above you need to have two NIC s in your laptop.. The modern ones always ship with an ethernet card and an wireless adapter.. So that shud suffice.

No Sound in Head Phone Jack for Dell 1588 on Lucid Lynx :

When you plug in the head phones, the sound from the speakers stop but you dont hear anything on your head phone .. Prob cos of your audio modules not properly configured. Times like this , you get to know of the countless number of sound cards out there in the market…. A complete official HowTo is available here. In short for a Dell Laptop with this problem, you gotta do this,

cat /proc/asound/card0/codec#* | grep Codec

This would give the model of your audio card on your system mine was

Codec: IDT 92HD73C1X5

Next you need to find the suitable audio model for this card from /usr/share/doc/alsa-base/driver/HD-Audio-Models.txt.gz.

zless /usr/share/doc/alsa-base/driver/HD-Audio-Models.txt.gz

Search for your card in that doc .. zless reads compressed text files 🙂 .. So search for 92HD73 in that text file.. sometimes the cards are wild carded so incase you dont find, keep searching with lesser number of characters from beginning . The text I found was ,

ref           Reference board
no-jd         BIOS setup but without jack-detection
intel         Intel DG45* mobos
dell-m6-amic  Dell desktops/laptops with analog mics
dell-m6-dmic  Dell desktops/laptops with digital mics
dell-m6       Dell desktops/laptops with both type of mics
dell-eq       Dell desktops/laptops
alienware     Alienware M17x
auto          BIOS setup (default)

So the one matching my case was dell-m6 . Find the appropriate one for your laptop and do the following :

echo “options  snd-hda-intel model=dell-m6″ | sudo  tee /etc/modprobe.d/alsa-base.conf

A restart should now get your laptop headphone jacks work normal 🙂 ..

The Low resolution in the splash screen and Grub during Boot up :

This is a traditional problem when your hard ware ( in this case your monitor) doesnt report the proper specs of display it can support. So specifying it manually solves the problem. Earlier, it was GRUB legacy and usplash until recently things begin to progress towards GRUB2 and plymouth. So here is a quick process to do it. My laptop supports 1920×1080 resolution. So replace that with your resolution wherever applicable. This mostly would happen also if you use 4GB ram + 1GB graphics card on windows XP or any other 32bit OSThis should solve the problem and you can see a very HD grub menu on your boot up 🙂 ..

First we need to install the v86d package which gives the backend for kernel drivers that execute the x86 BIOS code. So run sudo apt-get install v86d
The screen resolution settings for grub2 are in /etc/grub/default . The previous grub legacy would have it in /boot/grub/menu.list. Here you need to change the GRUB_CMDLINE_LINUX_DEFAULT= “quiet splash” to GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash nomodeset video=uvesafb:mode_option=1920×1080-24,mtrr=3,scroll=ywrap”.
Add GRUB_GFXMODE=1920×1080 to the end . A similar line with resolution as 640×480 would be commented with an # .. You can as well remove the # and change it over there instead.
Now run echo “uvesafb mode_option=1280×1024-24 mtrr=3 scroll=ywrap” | sudo tee /etc/initramfs-tools/modules. This takes care of custom made resolution for GRUB and needs the v86d package.. For more details, check out here.
And again run echo “FRAMEBUFFER=y” | sudo tee /etc/initramfs-tools/conf.d/splash.
sudo update-grub2 to generate the grub.cfg and sudo update-initramfs -u to generate the new splash screen.

Enabling your 32 bit OS to address your 4GB Ram + 1GB Graphics Card :

Now this is an interesting problem that I discovered when I opened my system monitor. To my surprise, I found that my OS only could address 3GB of memory. Theoretically a 32-bit OS can address 4GB of memory but since I had a 1GB graphics card, it could only address 3GB of RAM and 1GB of Graphics card. So I need to change my OS to 64 bit or have a PAE (Physical Address Extension) supported kernel. The Desktop version kernel doesnt support PAE, so you need to install a PAE supported kernel. Do the following

sudo apt-get install linux-headers-server linux-image-server linux-server

Reboot and do a free -m to confirm all your 4GB is addressable :).

Will be making a couple more tweaks on my machine, thanks to google :). So as they say, “Where is the fun when everything works out of the box… Think Linux!”

PS : @suren : I knw now u will try to say something abt mac … bring it on 😉

Written by Sathya Narayanan

June 24, 2010 at 1:38 pm

Posted in College life, computers, general, Linux

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Evanescent Thoughts

2011

Facebook Internship

Flash Player 10.2 Workaround to Copy Video Files

The Indian Scenario

Population :

The Indian Rat Race at Schools :

Why Brain Drain??

One month into the Grad Life !!

Finding Invisible Friends and Dynamically Updating Your Status in Google Chat using XMPP Scripts #linux #python #ubuntu

The Hyderabad Weekend

My days at Theoretical Comp Sci Lab @ IIT-M (TCS Lab)

Do IM Clients (Pidgin,Skype et al) Detect Subnets and Avoid wastage of Internet Bandwidth ?? #linux

Ubuntu Lucid Lynx Tweaks

The one Internet connection and Many Laptop Problem :

No Sound in Head Phone Jack for Dell 1588 on Lucid Lynx :

The Low resolution in the splash screen and Grub during Boot up :

Enabling your 32 bit OS to address your 4GB Ram + 1GB Graphics Card :

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