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SubjectRe: Linux-2.6.11 can't disable CAD
On Thu, 7 Apr 2005, Jan Harkes wrote:

> On Thu, Apr 07, 2005 at 11:16:14AM -0400, Richard B. Johnson wrote:
>> In the not-too distant past, one could disable Ctl-Alt-DEL.
>> Can't do it anymore.
> ...
>> Observe that reboot() returns 0 and `strace` understands what
>> parameters were passed. The result is that, if I hit Ctl-Alt-Del,
>> `init` will still execute the shutdown-order (INIT 0).
> Actually, if CAD is enabled in the kernel, it will just reboot.
> If CAD is disabled in the kernel a SIGINT is sent to pid 1 (/sbin/init).

No, that's not how it ever worked. There are parameters that are
available in the reboot-system call that define the operation that
will occur when the 3-finger salute occurs.

Execute man 2 reboot.

> So what you probably had in the not-too-distant past was a disabled CAD
> in the kernel _and_ you had modified the following line in /etc/inittab,

The systems to which I refer do not, and never even had a file-system,
much-less any inittab. That's SYS-V init stuff for interactive access.

> # What to do when CTRL-ALT-DEL is pressed.
> ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now
> AFAIK this hasn't ever really changed.
> Jan

The kernel's response (or the 'C' runtime-library interface) has
changed so that it is now possible for somebody at the keyboard
of a machine to destroy the machine's operation by executing
Ctl-Alt-Del. I don't know how long this potential catastrophe
has existed, but when the machine(s) were initially certified
there was no possible way for a user to kill the machine from
the keyboard.

It is possible that a 'C' runtime library was changed in the
tarket so it's not a kernel problem. I'm checking it out now.

Dick Johnson
Penguin : Linux version 2.6.11 on an i686 machine (5537.79 BogoMips).
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