Wikipedia:Reference desk/Archives/Computing/2007 October 20

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October 20

hosts file

Is there any way to protect a hosts file so that it can't be modified?--VectorPotential^Talk 00:35, 20 October 2007 (UTC)

On what OS? On Unix/Linux (etc.) /etc/hosts should already be protected so that only root can modify it (if it isn't, chmod it), and obviously you should only let trusted people and trusted programs run as root. Equally on Windows, /WINDOWS/SYSTEM32/drivers/etc/hosts should have its ACLs set so that only members of Administrators can access it, and again you should only have people and programs you trust running on an account that's a member of that group. -- Finlay McWalter | Talk 00:40, 20 October 2007 (UTC)

Yep. Put other accounts in a different user group, give them the same access priviliges as Administrator, then take away access to host for that group. So they're identical to administrator but hosts is inaccessable and they can't change the permission themselves --ffroth 00:42, 20 October 2007 (UTC)

I wonder if maybe on Windows you could write a program to simply open a file in exclusive mode and not close it. Make it a background process so it runs all the time. This way no one else--running as you (presumably an administrator for most people)-- could edit the file. --Silvaran 00:50, 20 October 2007 (UTC)

I'm running XP (which I of course should have mentioned up front) but what I was wondering, is there a way such that no one, not even myself logged in as an administrator could change it?--VectorPotential^Talk 00:53, 20 October 2007 (UTC)

Administrators can do everything (Froth and Silvaran's clever hacks might stop some odd program you want to reign in, but will be trivial for a human attacker to defeat). Administrators can install device drivers and so access physical disks and physical RAM. -- Finlay McWalter | Talk 01:00, 20 October 2007 (UTC)

I didn't actually think it would be possible, but I did wager that if anyone knew how to do it, they would be here.--VectorPotential^Talk 01:02, 20 October 2007 (UTC)

It's really a self-contradictory question, rather than a matter of know-how. An administrator is by definition all powerful; you're asking for a non-all-powerful all-powerful account. Now what you can do is make an ordinary user account in a specific group, and assign to that group the specific capabilities (as few as possible) that it absolutely barely needs in order to get the job done. It might end up with some capabilities that traditionally are given only to admins but wouldn't itself be an admin (although I can't vouch for how long it would contain a hacker; bet on "not long") -- Finlay McWalter | Talk 01:10, 20 October 2007 (UTC)

Administrators can do anything. That's why I said to give other people a slightly reduced account that can't edit hosts or install device drivers, and keep Administrator for just yourself --ffroth 03:52, 20 October 2007 (UTC)

How big is a "block" on a Wii?

When downloading things on the Wii's shopping channel, it says, "Blocks to Download"... how many bytes are in a single block? --Silvaran 01:04, 20 October 2007 (UTC)

I have no idea, but the Wii has 512 MiB of internal Flash memory, so just take that and divide with the total amount of blocks available. --Oskar 06:18, 21 October 2007 (UTC)

There are eight blocks in one MB. --24.249.108.133 20:06, 22 October 2007 (UTC)

SSL Facebook

I'm not too fluent with server side-scripts, but when entering the username and password for a Facebook account and after I press enter, am i sending some sort of SSL query to the Facebook servers? Acceptable 03:56, 20 October 2007 (UTC)

Yes; as the form submits to https://login.facebook.com/login.php; the https in the url shows it's SSL. You should note that SSL really isn't anything to do with scripting, it's offered by the web server itself, not any script engines that run on it. --Blowdart | ^talk 11:59, 20 October 2007 (UTC)

Most sites use an SSL encrypted connection to send log-in data (passwords), and then switch you back into normal HTTP (with a log-in cookie) after you have authenticated. Facebook is the same way. --24.147.86.187 14:32, 21 October 2007 (UTC)

Note: this provides almost no protection against users on the same network. i.e. Another user on your wireless network. Yes, they won't see your password just by viewing the network traffic but they can easily steal your session and access your account. (Even stealing your password isn't difficult. The attacker just modifies the clear text login page to send them the password before it's sent to facebook.)

Cables with ferrite cores

I was curious to the purpose of computer cords with ferrite core dongles? I notice some USB, Firewire, and power cords have a ferrite core attachment on them? Are they better than ones that don't? What purpose do they serve? --24.249.108.133 03:59, 20 October 2007 (UTC)

There is an article for some reason named ferrite bead (though I've never heard them called this) - they're there to reduce high frequency electromagnetic interference. (How they do this might be a question for the science desk)

So I suppose more is better - an it's not an expensive component - though 10 years ago I don't recall them existing at all - and I coped... —Preceding unsigned comment added by 87.102.17.46 (talk) 09:29, 20 October 2007 (UTC)

Entering password into CGI proxy

Are there risks associated with entering, for example, a Hotmail username and password into a CGI proxy? If the server was unsecure, could the server owner find my password? If so, how exactly does he/she do this? Thanks. Acceptable 04:13, 20 October 2007 (UTC)

Usually proxy servers have logs of traffic only, but I'm sure that it is possible that the owner could keep track of data thats coming and going, and simple do a database dump and comb through all of the data. However, Hotmail and most other e-mail clients use encryption, and it is very difficult, if not impossible, to decode passwords and such. Finding passwords sent in plain text is definitely possible, however. The Userboxer^Complain/_ubx 14:34, 20 October 2007 (UTC)

Duh, yes. The encryption keeps people from listening in on the connection, but once it gets to hotmail it's fully decrypted and the server can do whatever it wants with it- authenticate your login, mass email it to all microsoft employees, whatever. Usually for security they only store a hash of your password but don't count on it. Use lots of different passwords --ffroth 15:46, 20 October 2007 (UTC)

Anything going by http can be seen by the proxy. Anything going by https cannot. --h2g2bob (talk) 01:56, 21 October 2007 (UTC)

However, you can't use https over a CGI proxy (which we really should have a proper article on) — or, if you could, the proxy would be acting as a man-in-the-middle and would be able to see your passwords. Ultimately, if you use a proxy like that, you really have to trust the people running it not to record and abuse anything you send over it, because there's nothing stopping them from doing it if they want. —Ilmari Karonen (talk) 14:52, 21 October 2007 (UTC)

psu heating

my power supply is overheating.its a new one and i its the 3rd one in less than 6 months.i think there is something i in my system unit that consuming an abnormal amount of energy or is my power supply weak.the fans are o.k.i have confirmed.is there a way to check what eating the power? 2.can u boot from a flash disk? can u also boot from an external harddisk.our teacher says u cant,there a guy who tells me its possible.so whats what? —Preceding unsigned comment added by 212.49.89.182 (talk) 08:34, 20 October 2007 (UTC)

1. Could be, what's the rated wattage?

2. Yes, you can boot from anything that can store your OS (floppy, flash drive, external hard drive, USB key, whatever) as long as it's big enough to hold it! -Wooty [Woot?] [Spam! Spam! Wonderful spam!] 12:49, 20 October 2007 (UTC)

...and supported by your BIOS. --antilived^{T | C | G} 23:03, 20 October 2007 (UTC)

How do you know for sure your power supply is overheating?--Silvaran 05:04, 21 October 2007 (UTC)

If it is overheating, and can't supply your PC properly, consider that buying cheap PSUs is clearly a false economy (put the cost of those three together, and what could you have bought?). Mine is a ThermalTake Toughpower 700W and cost £80. Remember, the number of AMPs on the 12v rail(s) is important. Check the internet for thorough review of the topic of PSU choice. __Seans Potato Business 16:32, 22 October 2007 (UTC)

network

my sister has just bought a pc.i want to connect them.she is in an adjacent room.how do i go about it.do i just buy the network cable and interconnect them or? —Preceding unsigned comment added by 212.49.89.182 (talk) 08:36, 20 October 2007 (UTC)

Yes you could

Or there are wireless connection methods Wireless LAN ( Wi-Fi Bluetooth adaptors are often sold - check the prices in you local computer store for 'wireless networking adaptors' they typically can be connected by USB etc)

In general a network cable will be cheaper, more secure, and faster than a wireless method - the only drawback is that you have a cable to route from one place to the other.

By the way the usual cable/connection type is ethernet ethernet cable87.102.17.46 09:35, 20 October 2007 (UTC)

Take a look at a common type of the cable. --Kushal^t 15:25, 20 October 2007 (UTC)

Specifically you need a ethernet crossover cable. Just connect the network adapters and windows will figure it out. I don't know about linux --ffroth 15:43, 20 October 2007 (UTC)

Three questions, all on hard drives:

1. What is the largest single hard drive on the market at the moment. I've heard that a 4TB drive was released, but surely there are bigger sizes than that?
2. When your storing loads of large files (approx 700MB each for example), is it better to store them on one huge capacity HDD, or several smaller drives?
3. In terms of data recovery and universal usage, is it better to store files on portable HDDs or standard HDDs (ie internal vs external)?

Thanks for your help everyone!! xxx Hyper Girl 14:18, 20 October 2007 (UTC)

From your questions, it appears that you are looking for a JBOD. It is external to the computer, internally contains many small drives, uses RAID to try and avoid data loss, and is accessible by just about any computer. -- kainaw™ 14:35, 20 October 2007 (UTC)

I like this idea! How would I do this? My computer can only hold two HDD at a time. Can you buy a sort of holder that joins them up outside the computer and connects via USB or one HDD lead (satia i think they call it)? Hyper Girl 14:47, 20 October 2007 (UTC)

JBODs are enclosures that sit outside your box. There are many types now. Some are called NAS (Network Area Storage). You plug it into a router. Some are USB - you plug it right into your computer. The most common are some sort of SCSI. You'll need to get a SCSI card for your computer. Your computer sees it as a normal external drive. It doesn't have to deal with the internals of the JBOD. As for size, JBODs can get very large. I have an 8TB at work for backing up our database. That's considered small. Just make sure you pay attention to your JBOD. When one drive fails, your data is still intact (assuming the JBOD is using RAID). If two fail, you will likely lose all of your data. So, when a light turns from green to red/amber, you need to race out and get a replacement drive right away. -- kainaw™ 19:28, 20 October 2007 (UTC)

Kainaw, I don't believe you're using the term "JBOD" correctly. The physical thing which contains a bunch of disks is properly called a disk array. How it is logically set up makes it a JBOD (when all the disks are just logically concatenated as if they were one big disk) or a RAID (where more complex arrangements are used). -- Finlay McWalter | Talk 00:38, 21 October 2007 (UTC)

Hyper Girl: when you ask about what method is "better", you need to think about what characteristics you really want (which will allow you to define what "better" really means for your application). If you care solely about performance than RAID 0 is very fast (lots of spindles == lots of performance. If, however, you care most about absolute safety (if you data is very valuable, and you can't afford to lose data) then RAID 1 (a full copy of your data on each drive, which costs a lot but survives lots of nasty drive mishaps). And if you care about uptime (while having reasonable expectations for data safety too) then RAID 5 is for you. All of this is intended for users larger than a single person (a single 6 disk RAID-5 might be used for a workgroup of 20 people, or maybe a nerd with a particularly large pr0n collection) and larger and more sophisticated arrangements for larger groups or for specialist applications that are very data-intense. All of this costs - even a modest drive array typically costs thousands of dollars, which is a bargain for an enterprise user that depends on it, but might be offputting for you. If you can tell us more about your intended task, the organisational context, and your budget, we can get a bit more specific. -- Finlay McWalter | Talk 00:54, 21 October 2007 (UTC)

Hyper Girl: you also asked about whether external drives are right for you. As above, that depends on you requirements. External disks with a USB interface are fairly slow (because the USB interface itself is fairly slow) but pretty cheap. External disks with SCSI, SATA, and Fiber-channel interfaces are fast (just as fast as their internal counterparts). External USB drives really are intended for portability, so if you're using them always on the same machine in the same place, that's not ideal. As far as I'm aware the largest single-disk drive made now is around 750Gb; if you need several times that (at a fixed location) then you might consider just buying a bigger case for your computer (one with more drive bays, better cooling, and a bigger power supply) and transplanting you existing computer's guts into it. -- Finlay McWalter | Talk 01:15, 21 October 2007 (UTC)

Sorry for top posting but how often does the light go red in real life? --Kushal^t 20:32, 20 October 2007 (UTC)

I manage two JBODs. One has 8 drives. The other has 4. Out of the 12, I lose one drive every three months or so. The last two times, two drives went out within hours of each other - which made me look good for having up-to-date backups of the data. -- kainaw™ 22:42, 20 October 2007 (UTC)

It's good that you mention backups. I'll spare everyone my patented "RAID is not a backup" rant, but it's important to say that having a backup strategy that matches your storage needs (which again goes back to the specifics of the data) is just as important as having the live storage for in the first place. And the scary thing is that backup methods (tapes and stuff) aren't keeping pace with the growth of the arrays (and the drives they contain), so backing up to anything other than another array is becoming harder (and less pleasant) to do. If Hyper Girl is building a system for a business, she'll have to make one of those "what happens if x,y,z..." lists. Mine is pretty impressive, but even then it says we'll be okay if Godzilla or Mothra attacks; Godzilla and Mothra is too much for any plan to survive. -- Finlay McWalter | Talk 01:03, 21 October 2007 (UTC)

What do you do in case a hard drive fails? Do you just remove the bad one and stick in a brand new one? Does that mean you need to stockpile on unused hard disk drives? (Sorry, OP but I think this question might be helpful to you too.) --Kushal^t 23:26, 20 October 2007 (UTC)

If it's a JBOD you cry for a bit, because you just lost some data. If it's a RAID with increased reliability (like RAID 5) you indeed put in a new drive (operation of the whole array should be, from an external perspective, unaffected, as the array can survive losing a single disk). But most drive failures are just the drive firmware crashing (it happens remarkably often, with even the insanely expensive high-end fiber-channel drives) and resetting them (either from software or by pulling and replacing their caddy) often fixes them. -- Finlay McWalter | Talk 00:34, 21 October 2007 (UTC)

I read the RAID article and was wondering what would be the rebuilding time a new hard drive would need (for an ordinary 7200 rpm hard disk) after replacing a (really) broken hard disk. Can we calculate/estimate it from the disk's read write capacity? --Kushal^t 13:02, 21 October 2007 (UTC)

(for RAID 5) In theory the reconstruction time is the time it'll take to completely fill the fresh disk (which is a function of the disk's IO bandwidth and that of the bus into which its plugged), but in practice there's computational load handling the parities (higher end RAID-capable devices do parity in hardware, cheaper ones and software RAIDs do it in software) and IO slowdowns associated with ongoing access to the other disks have to handle while the RAID is dirty. So "several hours" isn't unreasonable (and as disk sizes seem to grow faster than disk speeds and bus bandwidths, that's set only to increase). If you're thinking "what happens if another disk fails during reconstruction?" then you'd be right to worry - it's a rare occurance but it'd kill a RAID-5. This is one reason that most RAID-capable arrays are configured to have one drive reserved as a hot-spare (so if you had an array with 16 disks, you'd generally configure it with a 15-disk RAID 5 and one hotspare), so the system can automatically recon to the hotspare without intervention. This reduces window in which RAID-5 is vulnerable to a two-disk failure, but doesn't close it. RAID 6 will survive a 2-disk failure. -- Finlay McWalter | Talk 13:21, 21 October 2007 (UTC)

Incidentally, if you're interested in messing around with RAID, but don't have a bunch of disks to actually try it out on, you can (on linux at least) use loopback devices and a software raid (manipulated with mdadm). You can even give one of your fake disks a fake error and sit and watch the fake raid reconstruct. Naturally you don't actually get any of the speed or reliability advantages of a real RAID, but it's fun to mess with. -- Finlay McWalter | Talk 14:44, 21 October 2007 (UTC)

Thanks everyone for you input. I'm not sure JBOD if for me. I'd been using six normal HDDs of about 16GB each, but pulling them out and restarting the PC each time was a grind. For now at least I'll try a largish portable HDD (maybe a 500GB one, I hear they sell for around $200). USB speed should be ok, it was mainly a space requirement problem (what with the lack of it). Thanks everyone! xxx Hyper Girl 13:37, 22 October 2007 (UTC)

Free DVD composition software

Ho there, old bean! What is a good DVD composition software, free or freeware, for either Windows XP or Xubuntu? I know about various DVD rippers, but I'm not looking for that sort of thing. I wish to make a slide show that is readable in a DVD player, consisting mostly of music and still pictures. I do appreciate your help! -L. G. Delacroix (216.178.50.6 19:04, 20 October 2007 (UTC))

I don't have a solution. I tried to look up Picasa but Picasa does not have the ability to create what you want. It does have a limited ability that plays back pictures on certain DVD players. See [1] --Kushal^t 23:24, 20 October 2007 (UTC)

Googling for linux dvd authoring turned up this Linux Journal article as the first hit. It seems to match what you're asking for pretty well. —Ilmari Karonen (talk) 14:44, 21 October 2007 (UTC)

computer search engine directories (email address removed)

Where can I find an outline of the basic characteristics of the different search engine directories. IE..how is google different thsn Yahoo? —Preceding unsigned comment added by 71.58.125.92 (talk) 21:20, 20 October 2007 (UTC)

^{Email address removed — Matt Eason (Talk • Contribs) 22:22, 20 October 2007 (UTC)}

A cursory glance reveals that List of search engines might be a good first place for you to go as (hopefully)other Wikipedians prepare a better answer for you. --Kushal^t 23:16, 20 October 2007 (UTC)

pfSense traffic shaper & Squid

I´ve got a pfSense gateway on my Lan with the Squid package installed and I want limit the speed of an IP. I went through the wizard with the penalty IP to that IP but that did nothing. Then I realised the connectin (flv) is going through the squid server so it´s not a direct WAN->LAN connection but 2 separate WAN->Squid & Squid->LAN connection, which doesn´t match the traffic shaping rules. How can I shape the Squid traffic? --antilived^{T | C | G} 21:28, 20 October 2007 (UTC)

No one here uses pfSense? --antilived^{T | C | G} 10:34, 21 October 2007 (UTC)

It's the weekend. Most folks who would know are probably out doing other things. Give it a little more time and someone may have an answer as the week goes on. -- Kesh 20:04, 21 October 2007 (UTC)

:( --Kushal^t 20:44, 21 October 2007 (UTC)

OpenOffice.org Calc question

Hi all:

I am using OpenOffice.org Calc to prepare a template for polls. I have a table where I can input data and in another sheet I have some graphs generated by that table. The only thing I haven't been able to do is get the graphs to update automatically when any cell in the table is changed. This seemed to happen at first, until I saved the document and closed it.

I don't really need them to update automatically. It would be enough to have a button that did this.

Any ideas? Thanks people! --Waldsen 23:29, 20 October 2007 (UTC)

Try the OOo forum (first google result for "ooo forum"). :) --Seans Potato Business 20:58, 23 October 2007 (UTC)