BH%SU-AI@USC-ECL (03/29/83)
From: Brian Harvey <BH%SU-AI@USC-ECL> Funny you should ask that question. The feature you want is running at the Lincoln-Sudbury Regional High School. I believe the relevant kernel code is on the 82.1 Usenix tape although I might be off by a year. The way it works is that the character ^_ (\037) is noticed in tty.c and the character you type after it is interpreted as a command. At LSRHS this happens even if your terminal is in raw mode, which I expect everyone will yell at me about, but that isn't an essential part of it if it offends you. (There is a "really raw" mode which is used only by uucico and which you have to be root to get into.) Some of the ^_ commands are processed directly by the kernel. These include ^_ K which does the equivalent of "kill -9 0"; ^_ I which does the equivalent of "reset" more or less; ^_ C which is like "kill 0". (Side comment: ^_ K is handy if you are about to log in as root and you are paranoid about someone maybe having written a login simulator, which is why this feature is made so hard to defeat.) Other ^_ commands are passed on to a program called daemon via a communication block in the kernel which daemon finds. These include ^_ T which runs "ps ltXXX" for your terminal, and ^_ R which tells you who is reserved for the terminal using a local reservation system. Anyway, just the other day one of my former students there invented ^_ L which tells you the load average. The whole ^_ feature is slightly kludgy and I'm afraid I've provoked a barrage of "that's not the Unix Philoosphy" messages by mentioning it, but let me tell you, now that I'm not at LSRHS anymore the thing I miss most when using other people's Unices is being able to type ^_ T.