XorgCtrlAltBackspace
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← Revision 61 as of 2010-06-12 04:57:24 ⇥
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| The Ctrl-Alt-Backspace key combination currently "zaps" (hard-restarts) the X server, and thus loses any unsaved data in applications, etc. This key combination is also largely undocumented, so users (probably ex-Windows users) may press this key combination without expecting data loss. This spec proposes to modify how this key combination works such that by default the user must hold the keys for 2 seconds in order for it to take effect. | The Ctrl-Alt-Backspace key combination currently "zaps" (hard-restarts) the X server, and thus loses any unsaved data in applications, etc. This key combination is also largely undocumented, so users (probably ex-Windows users) may press this key combination without expecting data loss. This spec proposes to follow upstream's lead and disable this key combination by default in order to prevent this usability issue from occurring in normal installs. |
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| The key combination of Ctrl-Alt-Backspace, which previously immediately exited X (and thus reset the graphics system back to the login screen), has been modified to require it to be held for 2 seconds before taking effect. This should help reduce the frequency of unexpected data loss and activity interruption for users unaware of its function that strike it accidentally. | The key combination of Ctrl-Alt-Backspace, which previously immediately exited X (and thus reset the graphics system back to the login screen), has been changed to disabled by default. It can be re-enabled by setting the DontZap xorg.conf option to False or by using the AltGr-SysReq-K key combination instead. This should help reduce the frequency of unexpected data loss and activity interruption for users unaware of its function that strike it accidentally. |
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| The key combination of Ctrl-Alt-Backspace terminates the user's current graphical shell, which can cause data loss if invoked accidentally. For some keyboards, backspace is in a location that can lead to accidentally hitting Ctrl-Alt-Backspace when using other Ctrl-Alt- key combinations. This can cause unexpected data loss and workflow interruption. | The key combination of Ctrl-Alt-Backspace terminates the user's current graphical shell, which can cause data loss if invoked accidentally. For some keyboards, backspace is in a location that can lead to accidentally hitting Ctrl-Alt-Backspace when using other Ctrl-Alt- key combinations. This can cause unexpected data loss and workflow interruption. It could also be seen as a form of local denial of service attack when people have access to the keyboard. |
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| However, disabling the key combination entirely would not be desirable, as it is an important way for exiting/restarting X that is useful particularly when X has locked up. A pop-up confirmation dialog is also not desirable, firstly because in one of the main use-cases for the key combo (a stuck Xorg), it's highly likely the window manager could not be depended on to display a dialog, and secondly because having a dialog would be an irritant both for accidental and intentional users. | Upstream has recently disabled this key combination by default, for many of the same reasons above. It makes sense for Ubuntu to follow their lead on this change. |
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| Making the key combination require being held for a couple seconds seems like a reasonable compromise. | Historically, it has been one mechanism for users to exit/restart X. Of course, there are other ways to restart. For "normal" logouts, the logout button on the panel or the ctrl-alt-delete combo is the preferred mechanism, as unlike ctrl-alt-backspace they are designed to shut down apps nicely and give the user several options on how to logout (hibernate, suspend, etc.) Ctrl-alt-delete includes a timeout mechanism so can work even if the display is not visible. Another use case for ctrl-alt-backspace is to restart a locked up X session. In many of these situations, ctrl-alt-delete will work as well. In some situations where ctrl-alt-delete won't work, neither will ctrl-alt-backspace, and so the power button will be the only recourse. For many non-technical users, the power button will be the most obvious mechanism anyway. Some users will not prefer this change. For these users, the DontZap option is available in xorg.conf to re-enable it. |
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| * Brian is a relatively new Ubuntu user working on a large image file in the GIMP, but also has Blender open on a different workspace which he used to render the image. Brian wants to close Blender as he is finished with it and needs to free up some memory for the GIMP. He tries pressing Ctrl-Alt-Backspace, like he used to do in Windows, to bring up a list of open applications so he can close Blender. The key combination does nothing so he decides to open the System Monitor from the System > Administration menu instead. Once Blender is closed he continues to work on his image in the GIMP, saving it when he is finished. | * Brian is a relatively new Ubuntu user working on a large image file in the GIMP, but also has Blender open on a different workspace which he used to render the image. Brian wants to close Blender as he is finished with it and needs to free up some memory for the GIMP. He remembers in Windows he could bring up an application list via Ctrl-Alt-Delete, but that doesn't work so he tries pressing Ctrl-Alt-Backspace. The key combination does nothing so he decides to open the System Monitor from the System > Administration menu instead. Once Blender is closed he continues to work on his image in the GIMP, saving it when he is finished. |
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| * Katie is writing a guide to help people who are used to Windows to migrate over to Ubuntu. She reads the help manuals for inspiration, then later she is experimenting to find similar functionality between the two systems that she can document. She avoids pressing Ctrl-Alt-Backspace and losing the document, which she has not saved yet, because she read in the help manuals that this would lose her work and send her back to the login screen. | * Elisee presses ctrl + alt + left or right to change from one workspace to another, and realizes that he wants to erase what he was writing on his IM program just before switching workspace, and accidentally hits backspace before releasing Ctrl and Alt. Thankfully, this didn't result in X exiting as it used to. He breaths a sigh of relief. |
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| * Joel's computer interface has frozen due to a graphics driver problem. He still has daemons running which need to remain open, so he cannot reboot. He remembered that Ctrl-Alt-Backspace would restart X, and is surprised at first that it doesn't restart immediately but he holds it down just in case, and after a couple seconds X restarts and he's back in business. He's curious why it didn't restart immediately, but after investigating it he learns that he can control the delay in his xorg.conf, but he doesn't mind the new behavior so leaves it as is. | * Joel's computer interface has frozen due to a graphics driver problem. He still has daemons running which need to remain open, so he cannot reboot. He remembered that Ctrl-Alt-Backspace would restart X, and is surprised that it doesn't restart immediately. Instead, he switches to a terminal console and restarts the gdm process and is back in business. After reading up on the change, he decides to re-enable DontZap in his xorg.conf to make things work the way he's accustomed to in the future. |
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| This spec assumes that users do not use the Ctrl-Alt-Backspace functionality regularly, and that those who do will not be terribly inconvenienced by having to hold it for 2 seconds. | This spec assumes that users do not use the Ctrl-Alt-Backspace functionality regularly, and that those who do will be able to change it back on in xorg.conf. |
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| A 2 second delay to the Ctrl-Alt-Backspace key combination will be added to xorg-server. | The DontZap option is changed to be True by default. |
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| A new 'ZapDelayTime' ServerFlag configuration parameter will be added for users to use in xorg.conf to control the delay before terminating the X session. Setting it to 0 will restore the old behavior, where X exits immediately. | |
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| * hw/xfree86/parser/xf86tokens.h: add ZAPDELAYTIME token * hw/xfree86/common/xf86Privstr.h: add zapDelayTime field * hw/xfree86/common/xf86Globals.c: set default value of zapDelayTime to 2 * hw/xfree86/common/xf86Config.c: add FLAG_ZAPDELAYTIME with call to xf86GetOptValBool() * hw/xfree86/parser/Flags.c add to ServerFlagsTab[] structure and xf86parseFlagsSection(void)'s case statement * hw/xfree86/xorgconf.cpp: Add "ZapDelayTime" option * hw/xfree86/doc/man/Xorg.man.pre man page * hw/xfree86/doc/man/xorg.conf.man.pre man page * hw/xfree86/utils/xorgconfig/xorgconfig.c xorg.conf template * hw/xfree86/common/xf86Events.c: Modify the KEY_BackSpace case branch in xf86CommonSpecialKey so it calls xf86ProcessActionEvent(ACTION_TERMINATE, NULL) only after zapDelayTime's configured time delay. * Need to record when the Press action started * On subsequent Press or Release actions, compare time to zapDelayTime * If Release happens before zapDelayTime, reset the delay timer * xkb/xkbActions.c: Ditto changes done to xf86Events.c |
1. We simply merge the upstream xserver codebase, with no Ubuntu changes required. 2. We search through our documentation for any instances where we are using ctrl+alt+backspace. We shouldn't be recommending this anywhere. 3. As part of the Xorg.conf Options Editor specification, GUI tools will be implemented that permit re-enabling this. Tools must be available for both GNOME and KDE. |
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| To test the implementation the keypress should be held for < 2 sec and if nothing happens until time == 2 sec, then it is successful. The ZapDelayTime parameter should be set to several values (0, 5, 100) and verified that the behavior is delayed by that amount of time. |
To test the implementation the keypress should be held, and X should not restart. |
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| Previous discussion has been taken into account with this version of the spec, and is archived at ["XorgCtrlAltBackspace/Discussion"]. | Previous discussion has been taken into account with this version of the spec, and is archived at [[XorgCtrlAltBackspace/Discussion]]. |
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| * http://bugs.freedesktop.org/show_bug.cgi?id=10507 -- Ctrl-Alt-Backspace should request confirmation before killing Xorg * http://bugs.freedesktop.org/show_bug.cgi?id=10510 -- Xorg should use a more unlikely key combination than Control-Alt-Backspace as the server zap key |
* http://bugs.freedesktop.org/show_bug.cgi?id=10507 -- Ctrl-Alt-Backspace should request confirmation before killing Xorg * http://bugs.freedesktop.org/show_bug.cgi?id=10510 -- Xorg should use a more unlikely key combination than Control-Alt-Backspace as the server zap key == Alternatives == For people coming here because they are missing the nice functionality of being able to kill the X server in case nothing else works anymore in the GUI, it might be interesting to know that x can now be killed with {{{"AltGr" - "SysReq" - K}}} ({{{AltGr}}} is the right Alt key. {{{SysReq}}} also labeled "Print, or "Druck" in Germany)! Found [[http://webupd8.blogspot.com/2009/04/ctrl-alt-backspace-disabled-in-most.html | here]]. |
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Please check the status of this specification in Launchpad before editing it. If it is Approved, contact the Assignee or another knowledgeable person before making changes.
Launchpad Entry: xorg-ctrl-alt-backspace
Packages affected:
Summary
The Ctrl-Alt-Backspace key combination currently "zaps" (hard-restarts) the X server, and thus loses any unsaved data in applications, etc. This key combination is also largely undocumented, so users (probably ex-Windows users) may press this key combination without expecting data loss. This spec proposes to follow upstream's lead and disable this key combination by default in order to prevent this usability issue from occurring in normal installs.
Release Note
The key combination of Ctrl-Alt-Backspace, which previously immediately exited X (and thus reset the graphics system back to the login screen), has been changed to disabled by default. It can be re-enabled by setting the DontZap xorg.conf option to False or by using the AltGr-SysReq-K key combination instead. This should help reduce the frequency of unexpected data loss and activity interruption for users unaware of its function that strike it accidentally.
Rationale
The key combination of Ctrl-Alt-Backspace terminates the user's current graphical shell, which can cause data loss if invoked accidentally. For some keyboards, backspace is in a location that can lead to accidentally hitting Ctrl-Alt-Backspace when using other Ctrl-Alt- key combinations. This can cause unexpected data loss and workflow interruption. It could also be seen as a form of local denial of service attack when people have access to the keyboard.
Upstream has recently disabled this key combination by default, for many of the same reasons above. It makes sense for Ubuntu to follow their lead on this change.
Historically, it has been one mechanism for users to exit/restart X. Of course, there are other ways to restart. For "normal" logouts, the logout button on the panel or the ctrl-alt-delete combo is the preferred mechanism, as unlike ctrl-alt-backspace they are designed to shut down apps nicely and give the user several options on how to logout (hibernate, suspend, etc.) Ctrl-alt-delete includes a timeout mechanism so can work even if the display is not visible.
Another use case for ctrl-alt-backspace is to restart a locked up X session. In many of these situations, ctrl-alt-delete will work as well. In some situations where ctrl-alt-delete won't work, neither will ctrl-alt-backspace, and so the power button will be the only recourse. For many non-technical users, the power button will be the most obvious mechanism anyway.
Some users will not prefer this change. For these users, the DontZap option is available in xorg.conf to re-enable it.
Use Cases
Brian is a relatively new Ubuntu user working on a large image file in the GIMP, but also has Blender open on a different workspace which he used to render the image. Brian wants to close Blender as he is finished with it and needs to free up some memory for the GIMP. He remembers in Windows he could bring up an application list via Ctrl-Alt-Delete, but that doesn't work so he tries pressing Ctrl-Alt-Backspace. The key combination does nothing so he decides to open the System Monitor from the System > Administration menu instead. Once Blender is closed he continues to work on his image in the GIMP, saving it when he is finished.
- Elisee presses ctrl + alt + left or right to change from one workspace to another, and realizes that he wants to erase what he was writing on his IM program just before switching workspace, and accidentally hits backspace before releasing Ctrl and Alt. Thankfully, this didn't result in X exiting as it used to. He breaths a sigh of relief.
Joel's computer interface has frozen due to a graphics driver problem. He still has daemons running which need to remain open, so he cannot reboot. He remembered that Ctrl-Alt-Backspace would restart X, and is surprised that it doesn't restart immediately. Instead, he switches to a terminal console and restarts the gdm process and is back in business. After reading up on the change, he decides to re-enable DontZap in his xorg.conf to make things work the way he's accustomed to in the future.
Assumptions
This spec assumes that users do not use the Ctrl-Alt-Backspace functionality regularly, and that those who do will be able to change it back on in xorg.conf.
Design
The DontZap option is changed to be True by default.
Implementation
1. We simply merge the upstream xserver codebase, with no Ubuntu changes required.
2. We search through our documentation for any instances where we are using ctrl+alt+backspace. We shouldn't be recommending this anywhere.
3. As part of the Xorg.conf Options Editor specification, GUI tools will be implemented that permit re-enabling this. Tools must be available for both GNOME and KDE.
Test/Demo Plan
To test the implementation the keypress should be held, and X should not restart.
Discussion
Previous discussion has been taken into account with this version of the spec, and is archived at XorgCtrlAltBackspace/Discussion.
External links
See also:
http://bugs.freedesktop.org/show_bug.cgi?id=10507 -- Ctrl-Alt-Backspace should request confirmation before killing Xorg
http://bugs.freedesktop.org/show_bug.cgi?id=10510 -- Xorg should use a more unlikely key combination than Control-Alt-Backspace as the server zap key
Alternatives
For people coming here because they are missing the nice functionality of being able to kill the X server in case nothing else works anymore in the GUI, it might be interesting to know that x can now be killed with "AltGr" - "SysReq" - K (AltGr is the right Alt key. SysReq also labeled "Print, or "Druck" in Germany)! Found here.
XorgCtrlAltBackspace (last edited 2010-06-12 04:57:24 by dhcp198-158)