Command Line – How to Soft Kill GUI Applications via Terminal

I believe the related man page is, XKillClient. You can use xdotool to simulate the close button being clicked from a terminal like so.

Example

Assuming I have a gnome-terminal open and it's name is "saml@grinchy:/home".

1. Get the window ID

   $ xdotool search --name "saml@grinchy:/home"
   96488188
   

2. Send it a Alt+F4

   $ xdotool windowactivate --sync 96488188 key --clearmodifiers \
        --delay 100 alt+F4
   

You can put them together by embedding the first command into the second:

$ xdotool windowactivate --sync $( ...1st command...) key --clearmodifiers \
         --delay 100 alt+F4

You can save yourself by letting xdotool do both at the same time:

$ xdotool search --name "saml@grinchy:~" key alt+f4

Globally

You can adapt what I've provided to run it on windows that have the same name:

$ xdotool search --name "saml@grinchy:~"
96488779
96468996

Or on windows by other attributes. You can use xwininfo to find out more about a particular window. Run it and then just click on the window of interest:

$ xwininfo

xwininfo: Please select the window about which you
          would like information by clicking the
          mouse in that window.

xwininfo: Window id: 0x5c04d4b "saml@grinchy:~"

  Absolute upper-left X:  14
  Absolute upper-left Y:  74
  Relative upper-left X:  14
  Relative upper-left Y:  74
  Width: 941
  Height: 361
  Depth: 32
  Visual: 0x62
  Visual Class: TrueColor
  Border width: 0
  Class: InputOutput
  Colormap: 0x5c00003 (not installed)
  Bit Gravity State: NorthWestGravity
  Window Gravity State: NorthWestGravity
  Backing Store State: NotUseful
  Save Under State: no
  Map State: IsViewable
  Override Redirect State: no
  Corners:  +14+74  -485+74  -485-465  +14-465
  -geometry 132x24+14+74

Other useful tools when dealing with X11 windows are xdpyinfo & xprop. xdpyinfo can be used to find out information about the X server. So you can figure out which window has focus:

$ xdpyinfo |grep focus
focus:  window 0x5c00005, revert to Parent

xprop and xwininfo can take a -id switch so you can provide them the Window ID that you're interested in instead of having to click on it:

$ xprop -id 0x5c00001|grep -i class
WM_CLASS(STRING) = "gnome-terminal", "Gnome-terminal"

References

• xwininfo man page
• xdpyinfo man page
• xprop man page

The instructions to disable xdm/kdm/gdm/whichever-dm-you-have is correct. If you don't do this, you boot to a graphical login (that's the dm = display manager), and then whenever you quit X (which should be as easy as ctrl-alt-backspace -- try it, but close your apps first), the DM will respawn another graphical login, making it impossible to escape the GUI.

Another possibility with debian is to check in /etc/rc[N].d for a runlevel which does not start the dm, and make that the initdefault in /etc/inittab. I don't have an unmodified debian system at hand, so I can't say which if any that will be -- possibly 2. Do not choose 0, 1, or 6.

Once the dm is disabled, you boot to a login console. From there you can start X with the command startx. This includes a default DE and if you've been using gnome that will probably be it. You can also create an ~/.xinitrc, which is a shell script which will be run in place of the default. Generally they can be pretty minimal, eg:

#!/bin/sh

exec gnome-session

Should start gnome (I believe -- I don't have a gnome system at hand either).

Note that you can't run a GUI application without X; it's not clear from your post you understand that. GUI programs are actually clients that need the Xorg server to work. You can start a bare X with no DE or WM and a specific application by replacing the exec gnome-session line with the name of the application, but beware you'll then have no way to start anything else and when you close that application, you'll be looking at a blank screen with a cursor floating in it.

There's nothing dangerous in all this and it is easy to re-enable the DM if you want.