SAK gives kernel panic
Anthony M. Rasat
anthony.rasat at gmail.com
Mon Nov 17 04:12:48 UTC 2008
ls199mp1505 at shaped.dsl.eca.co.za wrote:
> Ubuntu 8.10 Intrepid, 32-bits.
> First, switch to a text console , e.g. console_4
> with <ctrl><alt><f4>. Login as root.
> Then use loadkeys and assign the SAK key to
> e.g. <ctrl><alt><break>.
> Finally, press the SAK key. Result:
> attempt to kill init
> kernel panic
> Can be reproduced anytime.
> -- frank
Frank, frankly I have never heard of SAK key. So I asked goodie ol'
Google. Apparently the mighty Andrew Morton have a good explaination, as
Linux 2.4.2 Secure Attention Key (SAK) handling
18 March 2001, Andrew Morton <akpm[AT]osdl[DOT]org>
An operating system's Secure Attention Key is a security tool which is
provided as protection against trojan password capturing programs. It
is an undefeatable way of killing all programs which could be
masquerading as login applications. Users need to be taught to enter
this key sequence before they log in to the system.
>From the PC keyboard, Linux has two similar but different ways of
providing SAK. One is the ALT-SYSRQ-K sequence. You shouldn't use
this sequence. It is only available if the kernel was compiled with
The proper way of generating a SAK is to define the key sequence using
`loadkeys'. This will work whether or not sysrq support is compiled
into the kernel.
SAK works correctly when the keyboard is in raw mode. This means that
once defined, SAK will kill a running X server. If the system is in
run level 5, the X server will restart. This is what you want to
What key sequence should you use? Well, CTRL-ALT-DEL is used to reboot
the machine. CTRL-ALT-BACKSPACE is magical to the X server. We'll
In your rc.sysinit (or rc.local) file, add the command
echo "control alt keycode 101 = SAK" | /bin/loadkeys
And that's it! Only the superuser may reprogram the SAK key.
Anthony M. Rasat
Manager - Technical, Network and Support Division
PT. Jawa Pos National Network
Graha Pena Jawa Pos Group Building, 5th floor
Jln. Raya Kebayoran Lama 12, Jakarta Barat 12210
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