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theolein · Jun 16, 2002, 08:34 AM

I think most of us know what rm -rf does and how one should be careful with it. I saw a troll on slashddot yesterday with the sig "yes > /dev/hda1". I also saw something similar in another post "yes >/dev/mem".

Does anyone know (I am *not* going to try this out) if it is so simple to flood memory or the harddrive with "y"? Will this simply crash the machine after a while or will it overwrite data as well?

I am asking this because it intrigues me that something quite dangerous could be floating around for potentially unwary users.

IUJHJSDHE · Jun 16, 2002, 08:37 AM

It might crash with memory but I don't know about hd1.

In ANY case I think I will delete the binary from bin now <img border="0" alt="[Skeptical]" title="" src="graemlins/bugeye.gif" />

utidjian · Jun 16, 2002, 09:04 AM

<blockquote>quote:<hr />Originally posted by theolein:
I think most of us know what rm -rf does and how one should be careful with it. I saw a troll on slashddot yesterday with the sig "yes > /dev/hda1". I also saw something similar in another post "yes >/dev/mem".

Does anyone know (I am *not* going to try this out) if it is so simple to flood memory or the harddrive with "y"? Will this simply crash the machine after a while or will it overwrite data as well?

I am asking this because it intrigues me that something quite dangerous could be floating around for potentially unwary users.<hr /></blockquote>Yes... it is that easy to crash the machine... as root. And yes, you can possibly overwrite critical data on the hard drive... as root. That is why spaces in commands and filenames can have such devastating effects. Remember the little bug with, I think, iTunes update from Apple? IIRC it wiped out the second partition or disk if it happened to be named a certain way. Apple had it fixed within 24 hours. I'm sure if you do a search you can find the details somewhere in the forums.

Say you wanted to clear out some directory tree and wanted to do this (as root):

rm -Rf /junk

BUT instead you typed:

rm -Rf / junk (note the space)

Note: The above commands will only work as the root user.
I think that is one reason why Apple, by default, disables the root account and requires one to type sudo first. It won't prevent it from happening in all cases but it will put a hesitation in there.

A favorite quote:
<blockquote>quote:<hr />UNIX was not designed to stop you from doing stupid things, because that would also stop you from doing clever things. -- Doug Gwyn <hr /></blockquote>

[APi]TheMan · Jun 16, 2002, 12:57 PM

<blockquote>quote:<hr />Originally posted by theolein:
Does anyone know (I am *not* going to try this out) if it is so simple to flood memory or the harddrive with "y"? Will this simply crash the machine after a while or will it overwrite data as well?.<hr /></blockquote>Wow, that's a clever one... I think that unless you were root you would get a lot of permission errors until the command got to some area of the filesystem where it had permissions to overwrite.

Synotic · Jun 17, 2002, 03:15 AM

Has anyone created an updated rm app or some sort of safeguard so paranoid people like me can prevent it from happening? Like a friendly warning? Or just making it completely impossible? It would prevent apps from doing it.. me.. etc.. Possible? It's just scary to think.. :shudder:

Mactoid · Jun 17, 2002, 03:36 AM

<blockquote>quote:<hr />Originally posted by Synotic:
Has anyone created an updated rm app or some sort of safeguard so paranoid people like me can prevent it from happening? Like a friendly warning? Or just making it completely impossible? It would prevent apps from doing it.. me.. etc.. Possible? It's just scary to think.. :shudder:<hr /></blockquote>Get into the habit of using the -i flag with rm. Put it in an alias if you want, however you don't want to be to reliant on an alias if you ever use different systems. And of course, get OUT of the habit of always using the -f flag with rm!

I'm not saying you do that, but I imagine there are people who do, just as there are people who always use "kill -9" without trying nicer measures first. Bad stuff.

absmiths · Jun 21, 2002, 11:41 AM

<blockquote>quote:<hr />Originally posted by theolein:
When NASA first started sending up astronauts, they quickly discovered that ballpoint pens would not work in zero gravity. To combat the problem, NASA scientists spent a decade and $12 Billion to develop a pen that writes in zero gravity, upside down, underwater, on almost any surface including glass and at temperatures ranging from below freezing to 300C. The Russians used a pencil.<hr /></blockquote>theolein, it is amazing how long you will keep that stupid signature. It is almost as if you are trying to spread disinformation since I know of at least 2 times that the incorrect nature of this has been brought to your attention.

[APi]TheMan · Jun 21, 2002, 04:54 PM

<blockquote>quote:<hr />Originally posted by absmiths:
 <blockquote>quote:<hr />Originally posted by theolein:
When NASA first started sending up astronauts, they quickly discovered that ballpoint pens would not work in zero gravity. To combat the problem, NASA scientists spent a decade and $12 Billion to develop a pen that writes in zero gravity, upside down, underwater, on almost any surface including glass and at temperatures ranging from below freezing to 300C. The Russians used a pencil.<hr /></blockquote>theolein, it is amazing how long you will keep that stupid signature. It is almost as if you are trying to spread disinformation since I know of at least 2 times that the incorrect nature of this has been brought to your attention.<hr /></blockquote>Who cares, it's funny. hahaha.

piracy · Jun 22, 2002, 12:22 AM

<blockquote>quote:<hr />Originally posted by [APi]TheMan:
Who cares, it's funny. hahaha.

<hr /></blockquote>The only thing that would make it funny is if it was true.

But it's not.

So instead of being funny, it's just f*cking stupid.

In fact, not only is it not true, it's no where near anything that would even remotely resemble the truth.

<a href="http://www.snopes2.com/business/genius/spacepen.htm" target="_blank">http://www.snopes2.com/business/genius/spacepen.htm</a>

Moonray · Jun 22, 2002, 01:07 AM

<blockquote>quote:<hr />Originally posted by piracy:
 <blockquote>quote:<hr />Originally posted by [APi]TheMan:
Who cares, it's funny. hahaha.

<hr /></blockquote>The only thing that would make it funny is if it was true.

But it's not.

So instead of being funny, it's just f*cking stupid.

In fact, not only is it not true, it's no where near anything that would even remotely resemble the truth.

<a href="http://www.snopes2.com/business/genius/spacepen.htm" target="_blank">http://www.snopes2.com/business/genius/spacepen.htm</a><hr /></blockquote>I start to ask myself what or who is "f*cking stupid" here. Even the site you mention says "The lesson of this anecdote is a valid one".
True is that ballpoint pens don't work in zero gravity, that a pencil was used and that lots of money and effort was spent to develop a pen which would write under some abnormal conditions.
That's the facts and don't tell that quote would not come any close to them. If whoever wrote it took the freedom to not hold that close to the facts as you would like it (where your site isn't guaranteed to be correct either) to make it a fun reading for people and you feel offended and don't get the point then you can just ignore it.

-

Mactoid · Jun 22, 2002, 03:50 AM

Could we please not discuss theolein's sig ever again on these boards? I am personally tired of hearing about it myself. He is aware that the literal interpretation of his parable is incorrect, and he is in no way obligated to change it because of that.

If absmith, piracy or anyone else need to discuss it again, then send him a personal message or at least post in the lounge.

BTW, those Fisher Space Pens are really freaking cool

I had the matte black titanium one a few years ago, and not only did it look awesome and write well, it was one of the most perfectly balanced pens I ever twirled. Still, the number one twirling pen in my experience goes to the Parker Vector.

obDangerous command:
<blockquote>code:<hr /><pre style="font-size:x-small; font-family: monospace;">rm -rf `ls | sed $(($RANDOM%\`ls|wc -l\`+1))'!'d`</pre><hr /></blockquote>

[ 06-22-2002, 03:58 AM: Message edited by: Mactoid ]

Sword of Orion · Jun 23, 2002, 01:59 AM

I thought ALL Unix commands were dangerous!

I've run afoul of ipfw in the past - I was experimenting with setting up my own firewall rules, and got into a state where the OS wouldn't allow me to sudo so that I could flush the current rules. BTW, I don't have a root account on my machine. So, if I had the firewall rules script run at startup, things would get interesting. <img border="0" title="" alt="[Eek!]" src="eek.gif" />

BTW, please note that my comments regarding theolein's sig are located in MY sig. <img border="0" alt="[Skeptical]" title="" src="graemlins/bugeye.gif" />

Mskr · Jun 23, 2002, 08:13 PM

<blockquote>quote:<hr />Originally posted by [APi]TheMan:
 <blockquote>quote:<hr />Originally posted by theolein:
Does anyone know (I am *not* going to try this out) if it is so simple to flood memory or the harddrive with "y"? Will this simply crash the machine after a while or will it overwrite data as well?.<hr /></blockquote>Wow, that's a clever one... I think that unless you were root you would get a lot of permission errors until the command got to some area of the filesystem where it had permissions to overwrite.<hr /></blockquote>Actually, the permission check is just done on the /dev/hda1 file, not the contents of the hard drive, its partitions, or anything else. Since, in OS X, /dev/hda1 doesn't exist (at least it doesn't on MY machine), this is perfectly innocuous, twice over if you're not root. You will see that you still get a "permission denied" message, since you don't have access to write to /dev ('>' will create the file if it doesn't already exist, remember) it LOOKS like you're protected from overwriting /dev/hda1, but really, you'd have to be root and use /dev/disk0 or whatever drive/partition device you're trying to overwrite.

goatnet · Jun 23, 2002, 08:53 PM

I thought ALL Unix commands were dangerous!

Not as dangerous as setup.exe

absmiths · Jun 26, 2002, 05:43 PM

<blockquote>quote:<hr />Originally posted by Moonray:
I start to ask myself what or who is "stupid" here. Even the site you mention says "The lesson of this anecdote is a valid one".
True is that ballpoint pens don't work in zero gravity, that a pencil was used and that lots of money and effort was spent to develop a pen which would write under some abnormal conditions.
That's the facts and don't tell that quote would not come any close to them. If whoever wrote it took the freedom to not hold that close to the facts as you would like it (where your site isn't guaranteed to be correct either) to make it a fun reading for people and you feel offended and don't get the point then you can just ignore it.

-<hr /></blockquote>Read the rest of the quote that you started above... "The anecdote offered above isn't a real example of this syndrome, however."

If I say "theolein is an idiot" do you think most people will understand that to be an anecdote? I suppose the Good Times virus hoax was also an anecdote? No. The true anecdote here is that all space programs tried pencils, and they failed, for which a suitable replacement was found, and then employed by all space programs from then on.

There are enough valid incidents of waste in government that would make an accurate anecdote, but this story has been going around for over 30 years and people think it's true.

[ 06-26-2002, 05:54 PM: Message edited by: absmiths ]

Moonray · Jun 26, 2002, 06:21 PM

absmiths,

I read the whole thing, yes. And anecdotes are there to make people a little think after reading it, they don't claim to show the absolute truth.

Obviously this one can be understood in different ways and seems to have the capability to offend people (now that could be extra fun for those who don't feel offended).

I think it neither wants to say "the government wasted money" nor "the russians have been smarter". For me the message is simply "sometimes you spend that much effort in following a way to achieve something that you aren't aware of a most simple solution", you can watch this all day in real life. And getting this wisdom served in such a high tech anecdote and not as a trivial story about someone who could be you or me is just something what makes me smile, not more and not less.

-

ThunderP · Jun 27, 2002, 08:00 PM

in response to mactoid, what does

rm -rf `ls | sed $(($RANDOM%\`ls|wc -l\`+1))'!'d`

do? i understand the rm -rf part means delete, but what does the following line of code mean?

Mactoid · Jun 27, 2002, 09:14 PM

<blockquote>quote:<hr />Originally posted by ThunderP:
in response to mactoid, what does

rm -rf `ls | sed $(($RANDOM%\`ls|wc -l\`+1))'!'d`

do? i understand the rm -rf part means delete, but what does the following line of code mean?<hr /></blockquote>The rest of the line selects a random file from your current directory to be deleted

Also, I should have mentioned that it only works in bash or ksh. Not tcsh.

kidtexas · Jun 27, 2002, 11:59 PM

<blockquote>quote:<hr />Originally posted by Mactoid:
BTW, those Fisher Space Pens are really freaking cool

I had the matte black titanium one a few years ago, and not only did it look awesome and write well, it was one of the most perfectly balanced pens I ever twirled. Still, the number one twirling pen in my experience goes to the Parker Vector.
<hr /></blockquote>I see I am not the only person who buys pens based on twirling potential... i will have to check out this Parker Vector.

Mactoid · Jun 28, 2002, 05:27 PM

<blockquote>quote:<hr />Originally posted by kidtexas:
I see I am not the only person who buys pens based on twirling potential... i will have to check out this Parker Vector.

<hr /></blockquote>Of course, my pens get twirled more than they actually get written with these days. BTW, the Parker Vector's are great, but once I got one with a loose cap. That wasn't pretty, it would always fall off and bounce around on the floor in my classroom annoying everyone around me. Just a heads up

Gary Kerbaugh · Jun 29, 2002, 06:55 AM

<blockquote>quote:<hr />Originally posted by Synotic:
Has anyone created an updated rm app or some sort of safeguard so paranoid people like me can prevent it from happening? Like a friendly warning? Or just making it completely impossible? It would prevent apps from doing it.. me.. etc.. Possible? It's just scary to think.. :shudder:<hr /></blockquote>Hi Synotic,
   Cool handle. Yes, I prefer the more modern (last 20 years?) two step delete process. In the belief that even UNIX can be modernized with sufficient futzing, I've written a script that emulates rm, except that it users CpMac to move the files to the user's ~/.Trash directory. You can call it anything, "Delete_For_Dummies", but I call mine rm and put it in my path ahead of the executable. You can find the script at:

<a href="http://www.cs.ecu.edu/~kerbaugh/rm/rm.html" target="_blank">http://www.cs.ecu.edu/~kerbaugh/rm/rm.html</a>

   Being a script, my "rm" is much slower than the original. However, I find it preferable to "one-step oblivion"!

[APi]TheMan · Jun 29, 2002, 07:49 PM

<blockquote>quote:<hr />Originally posted by Gary Kerbaugh:
 <blockquote>quote:<hr />Originally posted by Synotic:
Has anyone created an updated rm app or some sort of safeguard so paranoid people like me can prevent it from happening? Like a friendly warning? Or just making it completely impossible? It would prevent apps from doing it.. me.. etc.. Possible? It's just scary to think.. :shudder:<hr /></blockquote>Hi Synotic,
   Cool handle. Yes, I prefer the more modern (last 20 years?) two step delete process. In the belief that even UNIX can be modernized with sufficient futzing, I've written a script that emulates rm, except that it users CpMac to move the files to the user's ~/.Trash directory. You can call it anything, "Delete_For_Dummies", but I call mine rm and put it in my path ahead of the executable. You can find the script at:

<a href="http://www.cs.ecu.edu/~kerbaugh/rm/rm.html" target="_blank">http://www.cs.ecu.edu/~kerbaugh/rm/rm.html</a>

   Being a script, my "rm" is much slower than the original. However, I find it preferable to "one-step oblivion"!<hr /></blockquote>Sweet, I considered making an alias to do this once. Good times, I'll check your script out, though.

Gul Banana · Jun 30, 2002, 12:12 PM

Very cool script. There's a bug in it though. Unless you change, in the function set_dir,<blockquote>code:<hr /><pre style="font-size:x-small; font-family: monospace;">sed 's/ //g'</pre><hr /></blockquote>to <blockquote>code:<hr /><pre style="font-size:x-small; font-family: monospace;">sed 's/[ \.]//g'</pre><hr /></blockquote>, you'll get a bunch of errors any time you try to rm a directory with bundles in it (ie, something.app, something.pbproj). It'll still work correctly without the change, it's just annoying.

[Edit: My proposed fix needed a fix itself

Thanks to Gary for pointing that out.]

[ 06-30-2002, 10:15 PM: Message edited by: Gul Banana ]

Gary Kerbaugh · Jul 1, 2002, 11:43 AM

<blockquote>quote:<hr />Originally posted by Gul Banana:
Unless you change, in the function set_dir,<blockquote>code:<hr /><pre style="font-size:x-small; font-family: monospace;">sed 's/ //g'</pre><hr /></blockquote>to <blockquote>code:<hr /><pre style="font-size:x-small; font-family: monospace;">sed 's/[ \.]//g'</pre><hr /></blockquote>, you'll get a bunch of errors any time you try to rm a directory with bundles in it (ie, something.app, something.pbproj).<hr /></blockquote>   Mr Banana (how graphic) is quite correct. It would throw errors with any directory containing a period. His fix, another improvement and fixes of other bugs that have arisen (even more graphic) are currently posted at the "site".