Red Hat ENTERPRISE LINUX 3 Reference Manual page 90

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— Kills all processes active in a virtual console. Also called the Secure Access Key (SAK), it is
k
•
often used to verify that the login prompt is spawned from
to capture usernames and passwords.
— Reboots the kernel without first unmounting file systems or syncing disks attached to the
b
•
system.
— Crashes the system without first unmounting file systems or syncing disks attached to the
c
•
system.
— Shuts off the system.
o
•
— Attempts to sync disks attached to the system.
s
•
— Attempts to unmount and remount all file systems read-only.
u
•
— Outputs all flags and registers to the console.
p
•
— Outputs a list of processes to the console.
t
•
— Outputs memory statistics to the console.
m
•
through — Sets the log level for the console.
0 9
•
— Kills all processes except
e
•
— Kills all processes except
i
•
— Kills all processes using SIGKILL (including
l
•
this System Request Key code.
— Displays help text.
h
•
This feature is most useful when using a development kernel or when experiencing system freezes.
Caution
The System Request Key feature is considered a security risk because an unattended console
allows an attacker to gain access to the system. For this reason, it is turned off by default.
Refer to
/usr/src/linux-2.4/Documentation/sysrq.txt
System Request Key.
— Defines the key code for the System Request Key (
• sysrq-key
— Defines whether or not the System Request Key is a chorded key combination.
• sysrq-sticky
The accepted values are as follows:
— [Alt]-[SysRq] and the system request code must be pressed simultaneously. This is the
0
•
default value.
— [Alt]-[SysRq] must be pressed simultaneously, but the system request code can be pressed
1
•
anytime before the number of seconds specified in
— Specifies the number of seconds allowed to pass before the system request code
• sysrq-timer
must be pressed. The default value is
— Indicates whether or not a non-GPL module is loaded.
• tainted
— No non-GPL modules are loaded.
0
•
— At least one module without a GPL license (including modules with no license) is loaded.
1
•
— At least one module was force-loaded with the command
2
•
— Sets the maximum number of threads to be used by the kernel, with a default
• threads-max
value of .
2048
using SIGTERM.
init
using SIGKILL.
init
/proc/sys/kernel/sysrq-timer
.
10
Chapter 5. The
and not a trojan copy designed
init
). The system is unusable after issuing
init
for more information about the
is the default).
84
insmod -f
proc
File System
.
.