If you press Ctrl-Alt-Del (or whatever key was assigned the keysym Boot by loadkeys) then either the machine reboots immediately (without sync), or init
is sent a SIGINT. The former behaviour is the default. The default can be changed by root, using the system call reboot(), see ctrlaltdel(8). Some init
's change the default. What happens when init
gets SIGINT depends on the version of init
used - often it will be determined by the pf entry in /etc/inittab
(which means that you can run an arbitrary program in this case). In the current kernel Ctrl-AltGr-Del is no longer by default assigned to Boot.
Name Default binding ------------------------------- Show_Memory Shift-Scrollock Show_Registers AltGr-ScrollLock Show_State Ctrl-ScrollLock Console_n Alt-Fn and Ctrl-Alt-Fn (1 <= n <= 12) Console_{n+12} AltGr-Fn (1 <= n <= 12) Incr_Console Alt-RightArrow Decr_Console Alt-LeftArrow Last_Console Alt[Gr]-PrintScreen Scroll_Backward Shift-PageUp Scroll_Forward Shift-PageDown Caps_On (CapsLock is a toggle; this key sets) Compose Ctrl-.
Ctrl-Alt-Fn Switch to VT n Ctrl-Alt-KP+ Next mode Ctrl-Alt-KP- Previous mode Ctrl-Alt-Backspace Kill XOn some motherboards, Ctrl-Alt-KP- and Ctrl-Alt-KP+ will be equivalent to pressing the Turbo button. That is, both will produce the scancodes 1d 38 4a ca b8 9d and 1d 38 4e ce b8 9d, and both will switch between Turbo (>= 25MHz) and non-Turbo (8 or 12 MHz). (Often these key combinations only function this way when enabled by jumpers on the motherboard.)
Perry F Nguyen (pfnguyen@netcom22.netcom.com
) writes: AMI BIOS has a feature that locks up the keyboard and flashes the LED's if the Ctrl-Alt-Backspace combination is pressed while a BIOS password is enabled, until the CMOS/BIOS password is typed in.
Ctrl-Alt-Fn Switch to VT n (from version 0.50; earlier Alt-Fn) Ctrl-Alt-PgDn Kill dosemu (when in RAW keyboard mode) (and many other combinations - see the dosemu documentation)
One symbol may be constructed using several keystrokes.
Note that there are at least three such composition mechanisms:
/usr/X11R6/lib/X11/locale/iso8859-1/Compose
.
See also Andrew D. Balsa's comments at http://wauug.erols.com/~balsa/linux/deadkeys/index.html.
In case your kernel was compiled with CONFIG_MAGIC_SYSRQ enabled (a feature that is present since Linux 2.1.43) there is a single key (defined in <linux/keyboard.h>
) to which special system functions are attached, regardless of the current keyboard mode. For the PC architecture this special key is, naturally, the Alt+SysRq key, and any of the two Alt keys will work. (Note that if CONFIG_MAGIC_SYSRQ was not enabled, the default action of this key is to return to the previous console.)
If you press this key, do not release it, and hit another key, a corresponding action is performed. The action is performed whether anybody is logged in or not, is root or not. For the details, see drivers/char/sysrq.c
. Since this feature is meant only for kernel hackers, that should suffice. Still, let me add a few remarks.
For the key r the keyboard mode is reset to K_XLATE. For the key k a SAK and console reset is done. For the key b the machine is rebooted immediately. (See, not something you want to have enabled on a production machine.) For the key o the power is turned off (when the machine is capable of that). For the key s an emergency sync is scheduled. For the key u an emergency read-only remount is scheduled. For the keys p,t,m various information is shown (namely the same information also shown for RAlt,RCtrl,RShift+ScrollLock). For the keys e,i,l all processes get a SIG_TERM or SIG_KILL, respectively; for l even the init process is killed. Digits set the log level. Anything else prints a short summary: SysRq: unRaw saK Boot Off Sync Unmount showPc showTasks showMem loglevel0-8 tErm kIll killalL
.
Note: These are very dangerous actions! And they do not use your keymap - indeed, are meant for emergency cases where the state of your keymap, or even of the entire kernel, is uncertain. If you use a dvorak keyboard - bad luck! Most other people will be able to survive: the dangerous letters A,M,Q,W,Y,Z that are differently placed on English, French and German keyboards, are not used for actions.