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Date: Thu, 7 Apr 2005 11:59:04 -0700
From: "Randy.Dunlap" <rddunlap@osdl.org>
To: linux-os@analogic.com
Cc: linux-kernel@vger.kernel.org
Subject: Re: Linux-2.6.11 can't disable CAD
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On Thu, 7 Apr 2005 11:16:14 -0400 (EDT) Richard B. Johnson wrote:

| 
| In the not-too distant past, one could disable Ctl-Alt-DEL.
| Can't do it anymore.

What should disabling C_A_D do?

| Script started on Thu 07 Apr 2005 10:58:11 AM EDT
| [SNIPPED leading stuff...]
| 
| mprotect(0xb7fe4000, 28672, PROT_READ|PROT_EXEC) = 0
| brk(0)                                  = 0x804a000
| brk(0x8053000)                          = 0x8053000
| reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, LINUX_REBOOT_CMD_CAD_OFF) = 0
| pause( <unfinished ...>
| _exit(0)                                = ?
| # exit
| Script done on Thu 07 Apr 2005 10:58:21 AM EDT

What program is that?  I'm just echoing 0 | 1 into
/proc/sys/kernel/ctrl-alt-del , is that equivalent?
or have you tried that?

| 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).

echo 0 > /proc/sys/kernel/ctrl-alt-del
  is same as CAD_OFF
echo 1
  is same as CAD_ON

I tested 2.4.28, 2.6.3, 2.6.9, 2.6.11, and all of them behaved
the same way for me.  If it's an issue with using a syscall
to change the setting, I'll be glad to look into that too.

observed behaviors:
CAD enabled + C_A_D keys => call machine_reboot()
  to reboot quickly, no normal shutdown sequence;
CAD disabled + C_A_D keys => kill init, go thru normal
  clean shutdown sequence;
are these the expected behaviors?

| A side note, while researching this problem, I think I found
| that LINUX_REBOOT_MAGIC2 is Linus' birthday (in hex). Maybe
| the problem is that he no longer observes his birthday?

---
~Randy
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