Computing desk
< April 25	<< Mar \| April \| May >>	April 27 >

Welcome to the Wikipedia Computing Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

April 26

ripping

whats a good free thing to rip youtube vids —Preceding unsigned comment added by Tom12350 (talk • contribs) 06:37, 26 April 2010 (UTC)[reply]

Check these out. BTW, the question above was asked by Tom12350 (talk). 24.189.90.68 (talk) 09:03, 26 April 2010 (UTC)[reply]

I have used keepvid.com. Graeme Bartlett (talk) 09:13, 26 April 2010 (UTC)[reply]

keepvid doesn't work all the time. I use freestudio's suite of programs that includes a youtube downloader. -- Buffered Input Output 12:54, 26 April 2010 (UTC)[reply]

I'd suggest this Mozilla-recommended plug-in. It works great and can be used for any Flash video. You also don't need to bother with website middlemen like keepvid.com.--el Aprel (^facta-_facienda) 20:10, 26 April 2010 (UTC)[reply]

Bluetooth headset and skype

I'm using a bluetooth earpiece headset with skype, but I'm having troubles. My dongle is by a (Japanese?) company called PCi (BT-MicroEDR2X) and the headset is a Logicet LBT somethingorother, and pairing works and I can use it with skype, but if I turn off the headset and turn it back on, it doesn't work anymore, even though it says it should be. If I delete the device, repair and reboot it, it works again, but every time I turn it off and on again it stops working. I'm a bit new to bluetooth, does this happen a lot? 210.254.117.185 (talk) 12:05, 26 April 2010 (UTC)[reply]

php question

In php, what might "$line[$j]" do? 82.43.89.71 (talk) 14:54, 26 April 2010 (UTC)[reply]

That is syntax for accessing an array. Here is the PHP Array manual. Such notation seems to indicate that somebody has previously stored several lines (maybe text, but it could be anything) and indexed with a counting variable. Nimur (talk) 16:08, 26 April 2010 (UTC)[reply]

Just elaborating: a $ before a name means it is a variable (a little bit of memory that contains a value—in PHP you can't tell from the variable use itself whether it is a number, or a string, or what). But if there are brackets [] at the end, it means, "this variable is an array", that is, you have multiple values inside it, each of which is referenced by a key (you can think of it as $array_name[$key_value]). So you have an array name $line, and the key is being referenced with the value in the variable $j. --Mr.98 (talk) 01:17, 27 April 2010 (UTC)[reply]

The same syntax is also used for accessing individual characters of a string. --grawity 19:51, 28 April 2010 (UTC)[reply]

Deleting entry history in Safari for Mac

Hi, when I type an edit description in the bar in WP it shows up past edit descriptions that I have entered. How can I remove these? I hope you understand my question, I don't think I worded it very well :D Chevymontecarlo. 17:19, 26 April 2010 (UTC)[reply]

Depending on your browser, you may find that highlighting the entry you want to delete and hitting the Delete key does what you want. --Phil Holmes (talk) 17:49, 26 April 2010 (UTC)[reply]

I'm not on my Mac at the moment but what Phil suggests sounds correct. For example, start typing a common entry. A list of past entries should show up below the text box. Arrow down to the one you'd like to delete and hit the delete or backspace keys. It should be removed from the list. Dismas|^(talk) 09:44, 28 April 2010 (UTC)[reply]

Workplace internet question

My work place blocks many websites from access. Is there a way I can connect to my home computer from work, and use its internet which is not restricted? I am very uninformed with computers, could there be a simple program that is not complicated? —Preceding unsigned comment added by 140.121.130.67 (talk) 17:20, 26 April 2010 (UTC)[reply]

What you want is a VPN server on your home computer and a VPN client on your work computer. That is complicated if you are very uninformed with computers. You could also set up a proxy server on your home computer and access it from work. Again, it is complicated and will likely be blocked from your work. Every place I've worked has blocked websites. If I need a website, I just ask and they allow access to it. I assume you are asking how to access sites that you should not be accessing from work. If so, you need to VPN to change networks or use a proxy. -- kainaw ™ 17:45, 26 April 2010 (UTC)[reply]

There are a number of ways of doing this, of which the most well known is probably www.logmein.com. However, (a) your workplace might also block access to that, and (b) you may find that using a method to bypass restrictions put in place by your employer leads you open to disciplinary action and may not be advisable. --Phil Holmes (talk) 17:47, 26 April 2010 (UTC)[reply]

An alternative method might be to install Tor. Your computer will be connecting to a Tor proxy server, not to the unauthorized websites. As Phil Holmes notes above, you will probably get in trouble, anyway; and your company may have measures in place to block access to Tor proxies. Comet Tuttle (talk) 17:55, 26 April 2010 (UTC)[reply]

Or Remote Desktop Connection. Jørgen (talk) 19:02, 26 April 2010 (UTC)[reply]

Would that work on a restricted computer? OP said he/she is at work, so their computers are likely limited user only. 82.43.89.71 (talk) 19:04, 26 April 2010 (UTC)[reply]

Keep in mind that your work computer may be monitored, etc. If you have to do some personal browsing from work (checking out other employment opportunities during a break, say) and want to avoid attention from management, get a mobile phone with internet and a wireless data plan and keep the activity completely separate from the company equipment and network. If you're planning to spend hours a day surfing ~~porn~~ wikipedia instead of working, rethink your plan. 69.228.170.24 (talk) 19:51, 26 April 2010 (UTC)[reply]

Another option would be to setup an SSH server on your home PC, make the connection from your work PC to your home PC with tunneling, and then setting your browser to run through a proxy. (It's really not that hard - there is a quick walk-through on Lifehacker). I use this method at my workplace to get around the content-filtering Websense. It's built into most all Linux and Macs, and can easily be added to Windows by using Cygwin. (Again, covered by Lifehacker, here.) Hope that helps! Remember, though, as others have stated: What you do at work will most likely be monitored. ^Avicenna_sis @ 07:33, 27 April 2010 (UTC)[reply]

Rather than trying to circumvent the internet restrictions placed on you by your employer, something that might get you fired if you persist, why not try to get the restriction lifted? Ask the IT guys why you cannot access the site you need to visit, a site that will help you do your work better (that is what you want to do, right?) Astronaut (talk) 14:32, 27 April 2010 (UTC)[reply]

I changed the question title to something more meaningful. Astronaut (talk) 16:59, 27 April 2010 (UTC)[reply]

Start program hidden

In windows, how can I start a program (say for example notepad.exe) without any visible window showing up, so that it can only be seen in task manager? 82.43.89.71 (talk) 17:45, 26 April 2010 (UTC)[reply]

Call ShellExecute with SW_HIDE as the last parameter. --Andreas Rejbrand (talk) 18:20, 26 April 2010 (UTC)[reply]

I don't understand, how do I "call" ShellExecute? Where do I download ShellExecute? If it matters, my computer doesn't have administrator rights. 82.43.89.71 (talk) 18:34, 26 April 2010 (UTC)[reply]

ShellExecute is a function of Windows API. You can call it from your own application, written in C, C++, C#, Delphi, VB, ..., or any programming language. That is, you need (a tiny amount of) programming to utilize this function. But of course - there might be existing apps that can help you. --Andreas Rejbrand (talk) 19:10, 26 April 2010 (UTC)[reply]

I don't have any programming knowledge, I just want to run existing programs like notepad.exe or whatever without showing the window. 82.43.89.71 (talk) 19:23, 26 April 2010 (UTC)[reply]

You'll need to do a small amount of programming to do this. Download AutoHotkey and write the following script. (Note the double comma.) 121.72.214.55 (talk) 20:46, 26 April 2010 (UTC)[reply]

Run, name-of-program-you-want-to-run.exe,, Hide

I tried but it just loads the program as normal. 82.43.89.71 (talk) 21:16, 26 April 2010 (UTC)[reply]

Computer Science

if i were ask to write the sort note on the following:- 1. Quick Sort 2. Shell sort what will be the answer of this quetion? —Preceding unsigned comment added by 41.190.2.158 (talk) 19:15, 26 April 2010 (UTC)[reply]

Quick Sort and Shell sort seem like the place to start. —Preceding unsigned comment added by 82.43.89.71 (talk) 19:26, 26 April 2010 (UTC)[reply]

/dev/random security for servers

Our article on /dev/random says that on Linux it relies on network traffic to provide the entropy on routers, so I'm assuming that's also the case for servers that don't have local input devices, or where the local input devices are rarely used. If so, how can we be sure an adversary with a botnet won't generate fake traffic that appears to have more entropy than it actually has, in order to help attack the RNG? Even if it doesn't make the RNG completely predictable, even partial predictability would be very helpful e.g. for cheating at online poker. Neon Merlin 19:29, 26 April 2010 (UTC)[reply]

/dev/random and /dev/urandom accumulate entropy over the whole running time of a system and should be pretty unpredictable after the system has been up for a while, but does indeed have predictability problems shortly after boot, and maybe when running on vm's etc. For that and other reasons, high security applications should use host security modules for random number generation and other security functions. /dev/urandom is good enough for most "normal" purposes. 69.228.170.24 (talk) 19:43, 26 April 2010 (UTC)[reply]

The entropy is derived from the timing (the jitter, really) of packets, not their content. As the article you cited notes, if you can influence, or monitor, the timing then you do gain some insight into the state of the system. The network isn't the only source; disk timing jitter is another, but as the article says diskless (and I'd guess SSD based as well) machines will have much less entropy there. To my mind anyone running a decent sized online gambling operation will need lots of unimpeachably random data, and would be very well advised to use a hardware random number generator. I can't find regulations for online gambling systems, but for slot machines the Nevada Gaming Control Board's technical standards here has some specification (in a rather abstract form) about the operation of the RNG. -- Finlay McWalter • Talk 19:50, 26 April 2010 (UTC)[reply]

Neon Merlin, given the direction of your past bunch of questions, you should probably read the book Security Engineering by Ross Anderson. 69.228.170.24 (talk) 19:55, 26 April 2010 (UTC)[reply]

I'm pretty sure that /dev/random is based on more than just network jitter, including hard-drive timings and possibly UI elements too. /dev/urandom is exactly the same as /dev/random except that it doesn't do any blocking when the entropy gets low. Shadowjams (talk) 21:09, 26 April 2010 (UTC)[reply]

The comment at the top of the the source code for /dev/random says that there are a number of different timing-based sources of entropy. Someone who is more OS-oriented than I am may be able to make better sense of the source code itself. Paul (Stansifer) 21:32, 26 April 2010 (UTC)[reply]

Anyway, even without evildoers attacking, there isn't enough entropy collected (or at least reported) to be useful for something like a gaming (edit: "gambling", really) site. The following program reports the amount of entropy collected, which (at least on my desktop) runs no higher than 128 bits/second, with me thrashing the disk, network, mouse, and keyboard.

entropy timer program (C source)

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <assert.h>

#define SLEEPYTIME 2
#define BUF_SIZE (1024)

int main (){
  int          fd; 
  ssize_t      readsize;
  uint8_t      buffer [BUF_SIZE];
  unsigned int timeslept;

  fd = open ("/dev/random", O_RDONLY | O_NONBLOCK);
  if(fd<0){
    perror("opening /dev/random");
    exit(EXIT_FAILURE);
  }

  while(1==1){
    timeslept=SLEEPYTIME-sleep(SLEEPYTIME);

    readsize = read(fd, buffer, BUF_SIZE);
    if(readsize <0){
      if(errno==EAGAIN){
	readsize=0;
      }
      else {
	perror("reading from /dev/random");
	exit(EXIT_FAILURE);
      }
    }
    
    printf("%u bytes in %u seconds, entropy yield=%.1f bytes per second\n", 
	   (unsigned int)readsize,
	   timeslept,
	   (double)readsize/(double)timeslept);

  } // while
}

-- Finlay McWalter • Talk 22:52, 26 April 2010 (UTC)[reply]

The entropy accounting in /dev/random is IMO not terribly reliable, but for most purposes (including online gaming) I think it's usually acceptable to use a cryptographic PRNG seeded from hardware entropy. For gaming, being able to reproduce the dealt hands is sometimes desirable for accountability purposes. The Fortuna (PRNG) algorithm is a somewhat more systematic way to keep stirring hardware randomness into a pseudorandom source than what random/urandom does. 69.228.170.24 (talk) 01:51, 27 April 2010 (UTC)[reply]

Non-admin-rights accounts

82.43 made an assertion above about limited-rights user accounts that made me think: Does anybody know of a survey that makes any conclusions about how many computers in the world are used by people who utilize accounts without admin rights? Phrased another way, at any given moment, out of all the PCs worldwide that have users sitting at them typing and mousing away, what percentage of them are logged in with admin rights? Comet Tuttle (talk) 19:47, 26 April 2010 (UTC)[reply]

To estimate that, I think we'd need some idea what percentage of computers are owned by individuals and what percentage by businesses (since the latter would be much less likely to be set up as single-user machines). Also, do you count servers that accept SSH and VPN logins? (The York University campus was still using the mainframe-and-dumb-terminals model as of 2003). Neon Merlin 13:46, 29 April 2010 (UTC)[reply]

How does my computer know the time?

It has been a while since I lost Internet access for a significant period of time, and yet even when I did not have the Internet at the time I turned it on, my computer seemed to know what time it is when first turned on, even though I always turn it off when not using it.Vchimpanzee · talk · contributions · 22:08, 26 April 2010 (UTC)[reply]

Your computer has a Real-time clock which has its own battery & keeps time even when the mains power is interrupted. For interest, computers can acquire the time from the internet through the good offices of a Time server, but this is not the primary way in which most computers keep time; in fact, time servers are normally used to adjust the time showing on your local PC, since the real time clock can deviate from actual time (i.e. lose or gains seconds over time) for reasons I don't fully comprehend. --Tagishsimon (talk) 22:14, 26 April 2010 (UTC)[reply]

It remembered the time the same way a normal clock does. All the internet does it make sure the time is accurate. 82.43.89.71 (talk) 22:12, 26 April 2010 (UTC)[reply]

The Nonvolatile BIOS memory article discusses the battery that sits on your motherboard to power the real-time clock. Comet Tuttle (talk) 23:37, 26 April 2010 (UTC)[reply]

How do you momentarily exclude certain labels from being visible while in your gmail inbox

Step by Step:

I log in to gmail
I am presented with my Inbox
My inbox has a lot of messages marked "Funworld" (I like Funworld so i subscribe to all their updates)
1. On this particular day, I am not in a fun mood, so I want to see everything *except* Funworld
__FILL_IN_THE_BLANK__
My inbox now shows only those messages that are *not* labeled with "Funworld"

What is the step I have to do at "fill in the blank" in order to get the view I want?

NoClutter (talk) 22:33, 26 April 2010 (UTC)[reply]

Search for -(label:Funworld).

The "Quick Links" or "Multiple Inboxes" extensions from Gmail labs may make this step faster for you if you do it frequently. Paul (Stansifer) 01:38, 27 April 2010 (UTC)[reply]

Alternatively, you can edit the filter that adds the "Funworld" tag to all those messages to also "bypass the Inbox"; then you'll never see the Funworld messages unless you explicitly want to. (I have no idea what Funworld is, but this is how I cope with my Facebook e-mails.) Jørgen (talk) 06:50, 27 April 2010 (UTC)[reply]