ia64/linux-2.6.18-xen.hg

view Documentation/SAK.txt @ 854:950b9eb27661

usbback: fix urb interval value for interrupt urbs.

Signed-off-by: Noboru Iwamatsu <n_iwamatsu@jp.fujitsu.com>
author Keir Fraser <keir.fraser@citrix.com>
date Mon Apr 06 13:51:20 2009 +0100 (2009-04-06)
parents 831230e53067
children
line source
1 Linux 2.4.2 Secure Attention Key (SAK) handling
2 18 March 2001, Andrew Morton <akpm@osdl.org>
4 An operating system's Secure Attention Key is a security tool which is
5 provided as protection against trojan password capturing programs. It
6 is an undefeatable way of killing all programs which could be
7 masquerading as login applications. Users need to be taught to enter
8 this key sequence before they log in to the system.
10 From the PC keyboard, Linux has two similar but different ways of
11 providing SAK. One is the ALT-SYSRQ-K sequence. You shouldn't use
12 this sequence. It is only available if the kernel was compiled with
13 sysrq support.
15 The proper way of generating a SAK is to define the key sequence using
16 `loadkeys'. This will work whether or not sysrq support is compiled
17 into the kernel.
19 SAK works correctly when the keyboard is in raw mode. This means that
20 once defined, SAK will kill a running X server. If the system is in
21 run level 5, the X server will restart. This is what you want to
22 happen.
24 What key sequence should you use? Well, CTRL-ALT-DEL is used to reboot
25 the machine. CTRL-ALT-BACKSPACE is magical to the X server. We'll
26 choose CTRL-ALT-PAUSE.
28 In your rc.sysinit (or rc.local) file, add the command
30 echo "control alt keycode 101 = SAK" | /bin/loadkeys
32 And that's it! Only the superuser may reprogram the SAK key.
35 NOTES
36 =====
38 1: Linux SAK is said to be not a "true SAK" as is required by
39 systems which implement C2 level security. This author does not
40 know why.
43 2: On the PC keyboard, SAK kills all applications which have
44 /dev/console opened.
46 Unfortunately this includes a number of things which you don't
47 actually want killed. This is because these applications are
48 incorrectly holding /dev/console open. Be sure to complain to your
49 Linux distributor about this!
51 You can identify processes which will be killed by SAK with the
52 command
54 # ls -l /proc/[0-9]*/fd/* | grep console
55 l-wx------ 1 root root 64 Mar 18 00:46 /proc/579/fd/0 -> /dev/console
57 Then:
59 # ps aux|grep 579
60 root 579 0.0 0.1 1088 436 ? S 00:43 0:00 gpm -t ps/2
62 So `gpm' will be killed by SAK. This is a bug in gpm. It should
63 be closing standard input. You can work around this by finding the
64 initscript which launches gpm and changing it thusly:
66 Old:
68 daemon gpm
70 New:
72 daemon gpm < /dev/null
74 Vixie cron also seems to have this problem, and needs the same treatment.
76 Also, one prominent Linux distribution has the following three
77 lines in its rc.sysinit and rc scripts:
79 exec 3<&0
80 exec 4>&1
81 exec 5>&2
83 These commands cause *all* daemons which are launched by the
84 initscripts to have file descriptors 3, 4 and 5 attached to
85 /dev/console. So SAK kills them all. A workaround is to simply
86 delete these lines, but this may cause system management
87 applications to malfunction - test everything well.