On 2011-12-26, at 13:11 PM, Warren Toomey wrote: 'kill -1 1' will bring terror to anyone who had the misfortune of dealing with Xenix. I think the writer is getting at how UNIX bypassed the 'i ask you three times' dance. --lyndon

--- On Mon, 12/26/11, Armando Stettner <aps(a)ieee.org> wrote: I, of course, liked the warning from dump(1): "Are you sure you know what you are doing?" ... or the even scarier "Last chance before scribbling on hp(0,0)" from restor ...

When I worked at a university, one of our linux web servers crashed one day. In place of /dev/null was a history file. The last entry? mv .bash_history /dev/null Ah, script kiddies... On Dec 26, 2011 3:28 PM, "A. P. Garcia" <a.phillip.garcia(a)gmail.com> wrote:

Michael Davidson wrote: Sure. I was just tempted to exaggerate this discussion with: "init 0, halt or shutdown". But such commands had no been implemented even in 7th ed, yet :) I wonder if Warren rather had different issues in mind, which would lead to "unexpected" downs. The previously mentioned resource problems probably match this--not too suprisingly, because I always had the impression that Unix aimed at protecting processes from each other, not users. I'd like to remind of an according, earlier, quite fitting discussion from DMR: In "The UNIX Time-sharing System--A Retrospective" the paragraph "Security" http://cm.bell-labs.com/cm/cs/who/dmr/retro.html -Sven

On Mon, 12/26/11, Warren Toomey <wkt(a)tuhs.org> wrote: On Wed, Dec 28, 2011 at 01:13:54AM +0100, Sven Mascheck wrote: I just took umbrage at the article, in that it implied Unix provided machanisms for the ordinary user to "bring the system down". This is, of course, not true, at least once the hardware supported inter-process and kernel protection. However, it does remind me of Dennis' story about the days before proper memory protection (from http://cm.bell-labs.com/cm/cs/who/dmr/odd.html): Back around 1970-71, Unix on the PDP-11/20 ran on hardware that not only did not support virtual memory, but didn't support any kind of hardware memory mapping or protection, for example against writing over the kernel. This was a pain, because we were using the machine for multiple users. When anyone was working on a program, it was considered a courtesy to yell "A.OUT?" before trying it, to warn others to save whatever they were editing. At some point several were sitting around working away. Bob Morris asked, almost conversationally, "what are the arguments to ld?" Someone told him. We continued typing for the next minute, as a thought began to percolate, not quite to the top of the brain -- in other words, not quite fast enough. The terminal stopped echoing before anyone could stop and say "Hold on Bob, what is it you're trying to do?" Cheers, Warren

Great read. Would just like to add that on some Unixes a simple command with no args will bring a system down - killall. Adam

The one that has stuck with me since the first time I read it 30 years ago is from an article titled "On the Security of UNIX" (dmr, 1978?) ... Here is a particularly ghastly shell sequence guaranteed to stop the system: while :; do mkdir x cd x done Either a panic will occur because all the i-nodes on the device are used up, or all the disk blocks will be consumed, thus preventing anyone from writing files on the device. (from the UNIX programmer's manual, vol.2 p.592) ---corey

asbesto scripsit: Well, that version depends on shell functions, a relatively modern (in TUHS terms) feature of the shell. A more classical fork bomb, which will run on every shell, is to place the following into a file: $0 & $0 & and execute the file. -- John Cowan cowan(a)ccil.org http://ccil.org/~cowan If a soldier is asked why he kills people who have done him no harm, or a terrorist why he kills innocent people with his bombs, they can always reply that war has been declared, and there are no innocent people in an enemy country in wartime. The answer is psychotic, but it is the answer that humanity has given to every act of aggression in history. --Northrop Frye