The meaning and command executed on Ctrl+Alt+Del in Linux

keyboard shortcutslogoutreboot

In my gnome GUI desktop of Ubuntu 12.04, Ctrl+Alt+Delete will log out instead of rebooting.

But I was told that

Switching to a text-based virtual console and pressing Ctrl+Alt+Delete
will reboot the machine. It will shut down cleanly and reboot, which
is much better than Alt+SysRq+REISUB.

So I wonder if the above two different meanings of Ctrl+Alt+Delete are right?

What commands Ctrl+Alt+Delete is binded to in these two cases?

Best Answer

Ctrl+Alt+Delete is actually a "magic" keystroke for the IBM PC-compatible hardware architecture that would call a BIOS reset.

Since this kind of thing is dangerous for a system like Linux the decision was made to hook those keystrokes and do something else instead. This is controlled by init and you can see what it does by looking in /etc/inittab.

On my Debian Squeeze system:

ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now

Windows NT later followed suit and turned Ctrl+Alt+Delete into the secure key entry mode*.

In the case of X, it is similarly hooking the keystrokes but it simply kills the display server (which will automatically respawn if you're using a display manager).

Some systems (perhaps all, I haven't tried in a while) you can still press Ctrl+Alt+Delete before the OS loads to trigger a BIOS reset.

*I'm not sure what they actually call it.

Related Solutions

How to shutdown, reboot and logout the system from the command-line

Using the commands shutdown and reboot respectively. To log off from a terminal you can press Ctrl-D or type exit.

Bash – How to bind Ctrl+arrows/backspace/del to the Readline commands

Something like this:

"\e[1;5C": forward-word
"\e[1;5D": backward-word
"\e[H": beginning-of-line
"\e[F": end-of-line
"\eOH": beginning-of-line
"\eOF": end-of-line
"\e[1~": beginning-of-line
"\e[4~": end-of-line

Depending on the terminal settings and whether you're using screen, xterm would send those variations for Home and End, while the Control modified-cursor keys send a consistent value. You could change that (with xterm: other terminals generally not).

The control/Del and control/backspace probably won't work, unless by Del you mean the lower-left key on the 6-key editing keypad. For xterm, that sends "\e[3;5~".

With putty, you have few choices for "ctrlarrows" because it uses the control-modifier to switch between the normal and application modes of the cursor keys. That is, you'd toggle between "\e[C" (normal) and "\eOC" (application). Also, it's possible to change the home/end (to what putty's developers called "rxvt") to get the "\e[H" mentioned above.

Best Answer

Related Solutions

How to shutdown, reboot and logout the system from the command-line

Bash – How to bind Ctrl+arrows/backspace/del to the Readline commands

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