6 ms·

Indeed the feature is undocumented, but it's been known for some time - its goal is to mimic as much as possible the reset button, for those situations when you

by dend 4y ago

Indeed the feature is undocumented, but it's been known for some time - its goal is to mimic as much as possible the reset button, for those situations when your computer freezes up to a point where Ctrl+Alt+Del works, but literally no other process responds. Think "Background process locked up my OS, and I can't do anything short of unplugging the computer." Especially helpful on a laptop where the physical reset button is not available.

forgotpwd16 4y ago
What always found impressive on Windows is C-A-Del will always work.
- hammyhavoc 4y ago
  I can name hundreds of occasions from first-hand experience where it hasn't worked in the past 26 years for me on a variety of machines in various environments.
  - memcg 4y ago
    Me too.
  - beebmam 4y ago
    Blue screen of death, for example.
  - nyanpasu64 4y ago
    One prominent example I've seen multiple times, is hanging in the shutdown screen where no text appears under the spinning dots, and Ctrl-Alt-Del does nothing.
- jkingsman 4y ago
  Ctrl+Alt+Del invokes WinLogon, the highest priority process, that then delivers the task manager. I believe this is a kernel invocation, so regardless of user land dysfunction, it will always work. Tthis is possibly attributable as much to convenience as it is to security -- the Secure Attention Sequence[1] is intended as a login-spoofind protection which will suspend other tasks (like a spoofed login screen) before continuing forward with user auth. [1]: https://en.wikipedia.org/wiki/Secure_attention_key https://en.wikipedia.org/wiki/Secure_attention_key
  - theevilsharpie 4y ago
    > I believe this is a kernel invocation, so regardless of user land dysfunction, it will always work. It may always work from the kernel's standpoint, but this doesn't necessarily make it usable. Anything that blocks the display of WinLogon (e.g., the GPU has crashed and is unresponsive) would render this emergency restart mechanism unusable, and typically, situations like this are usually the only time I would need such a feature.
  - rzzzt 4y ago
    A group policy can be enabled on most variants of Windows (dating back to around NT 4 or Windows 2000, I think) to start with a dialog saying "Press Ctrl-Alt-Delete to begin", and pretty much nothing else, exactly for the reasons you describe.
    - WorldMaker 4y ago
      Though Microsoft's current security recommendation is against setting that policy for accessibility reasons. [0] Windows since 8 has worked on hardening/strengthening the "Secure Desktop" that login flows (and UAC prompts) happen on so that as much as possible malware shouldn't be able to run in those sandboxes. [0] https://docs.microsoft.com/en-us/windows/security/threat-protection/security-policy-settings/interactive-logon-do-not-require-ctrl-alt-del https://docs.microsoft.com/en-us/windows/security/threat-pro...
  - AllegedAlec 4y ago
    So what if the keypresses never get registered?
- WatchDog 4y ago
  I feel like it worked more reliably in XP and below, ever since vista I’ve had less success. With that said, system stability as a whole seems to have improved dramatically since those days, I don’t need to reach for it very often.
- ls612 4y ago
  I had a situation a month ago where my computer froze up (it was a couple months old at the time) and literally nothing would respond, even control-alt-delete, but my mouse cursor would still move around. I have no idea what caused that (it was a fresh restart after installing a GPU driver) but whatever drives the cursor display must be even higher priority than C-A-Del.
  - pretdl 4y ago
  - crdotson 4y ago
    Most graphics cards implement a hardware mouse cursor where the video card reads the current pointer location from memory and overlays the cursor on the screen. So I guess if the driver for the mouse and the video driver are both still running (the kernel hasn’t stopped completely) that will still work even if Winlogin is screwed to the point where it can’t show the CTRL-ALT-DEL screen. Happy to be corrected by someone who knows more about the windows kernel. :)
    - ls612 4y ago
      Interesting I didn’t know that. Some part of the kernel was fucked for sure as even the hardware sleep button in my keyboard didn’t work but I guess if the display driver was functioning that would be all that was needed.
malfist 4y ago
I wonder why microsoft never implemented the Magic SysRq keys like linux: https://en.wikipedia.org/wiki/Magic_SysRq_key https://en.wikipedia.org/wiki/Magic_SysRq_key It'd let you safely shutdown when the computer is locked up otherwise.
- kllrnohj 4y ago
  The times my Linux installs have locked up, those keys never worked.
  - malfist 4y ago
    They always worked for me, but it's been a long time since linux has locked up on me.
  - pengaru 4y ago
    They may be disabled by distros to enhance security against physical access attacks. It can also be challenging to actually input a magic-sysrq combo on many modern keyboards where sysrq isn't its own key, if it's labeled at all as some Fn-key contortion.
    - nyanpasu64 4y ago
      Personally I value being able to trigger oomkiller early when a process is eating up RAM, and being able to SIGKILL kwin_x11 on Nvidia or whatever other process is wedging Linux shutdown, instead of waiting multiple minutes for systemd to give up waiting and SIGKILL it directly. In terms of physical access attacks, it's just as viable and far more powerful to add a keylogger to my keyboard or Linux distro, or pull and image my hard drive, than to gasp kill processes or sync filesystem data to disk, oh the horror!
      - pengaru 4y ago
        WRT the physical security argument in favor of disabling sysrq, my assumption is it's more aimed towards defeating quick-n-dirty mischief style abuse. Ages ago I worked with a small team of young sysadmins who would often cause trouble for one another abusing things like sysrq, or poorly configured XFree86 instances without DontZap enabled (ctrl-alt-backspace termination, to a shell when startx/xinit is being used). Most of the time nothing malicious was actually done. But when you return to your screen-locked X desktop to find a fullscreen VC with a root shell blinking back at you and an empty history, guess what you'll at least have on the back of your mind for the rest of the workday?
deleted 4y ago
[deleted]
robonerd 4y ago
> Especially helpful on a laptop where the physical reset button is not available. Are there any where holding the power button for 10-15 seconds doesn't work? This has always been a reliable technique for me, when using linux on numerous different laptops from different manufacturers.
- Kwpolska 4y ago
  Remote access?
  - deleted 4y ago
    [deleted]
- WorldMaker 4y ago
  BIOS issues? Though Ctrl+Alt+Delete might not work with a BIOS acting up either.
- kkfx 4y ago
  That's ACPI shutdown, not OS-specific but motherboard specific AFAIK, it should work an all ACPI compliant systems...
  - netsharc 4y ago
    Indeed. And afaik, the specs say hold it for 4 seconds
- hulitu 4y ago
  15 seconds migh be a lotof time, depending on the situation.

by dend 4y ago

forgotpwd16 4y ago

What always found impressive on Windows is C-A-Del will always work.

hammyhavoc 4y ago
I can name hundreds of occasions from first-hand experience where it hasn't worked in the past 26 years for me on a variety of machines in various environments.
- memcg 4y ago
  Me too.
- beebmam 4y ago
  Blue screen of death, for example.
- nyanpasu64 4y ago
  One prominent example I've seen multiple times, is hanging in the shutdown screen where no text appears under the spinning dots, and Ctrl-Alt-Del does nothing.
jkingsman 4y ago
Ctrl+Alt+Del invokes WinLogon, the highest priority process, that then delivers the task manager. I believe this is a kernel invocation, so regardless of user land dysfunction, it will always work. Tthis is possibly attributable as much to convenience as it is to security -- the Secure Attention Sequence[1] is intended as a login-spoofind protection which will suspend other tasks (like a spoofed login screen) before continuing forward with user auth. [1]: https://en.wikipedia.org/wiki/Secure_attention_key https://en.wikipedia.org/wiki/Secure_attention_key
- theevilsharpie 4y ago
  > I believe this is a kernel invocation, so regardless of user land dysfunction, it will always work. It may always work from the kernel's standpoint, but this doesn't necessarily make it usable. Anything that blocks the display of WinLogon (e.g., the GPU has crashed and is unresponsive) would render this emergency restart mechanism unusable, and typically, situations like this are usually the only time I would need such a feature.
- rzzzt 4y ago
  A group policy can be enabled on most variants of Windows (dating back to around NT 4 or Windows 2000, I think) to start with a dialog saying "Press Ctrl-Alt-Delete to begin", and pretty much nothing else, exactly for the reasons you describe.
  - WorldMaker 4y ago
    Though Microsoft's current security recommendation is against setting that policy for accessibility reasons. [0] Windows since 8 has worked on hardening/strengthening the "Secure Desktop" that login flows (and UAC prompts) happen on so that as much as possible malware shouldn't be able to run in those sandboxes. [0] https://docs.microsoft.com/en-us/windows/security/threat-protection/security-policy-settings/interactive-logon-do-not-require-ctrl-alt-del https://docs.microsoft.com/en-us/windows/security/threat-pro...
- AllegedAlec 4y ago
  So what if the keypresses never get registered?
WatchDog 4y ago
I feel like it worked more reliably in XP and below, ever since vista I’ve had less success. With that said, system stability as a whole seems to have improved dramatically since those days, I don’t need to reach for it very often.
ls612 4y ago
I had a situation a month ago where my computer froze up (it was a couple months old at the time) and literally nothing would respond, even control-alt-delete, but my mouse cursor would still move around. I have no idea what caused that (it was a fresh restart after installing a GPU driver) but whatever drives the cursor display must be even higher priority than C-A-Del.
- pretdl 4y ago
- crdotson 4y ago
  Most graphics cards implement a hardware mouse cursor where the video card reads the current pointer location from memory and overlays the cursor on the screen. So I guess if the driver for the mouse and the video driver are both still running (the kernel hasn’t stopped completely) that will still work even if Winlogin is screwed to the point where it can’t show the CTRL-ALT-DEL screen. Happy to be corrected by someone who knows more about the windows kernel. :)
  - ls612 4y ago
    Interesting I didn’t know that. Some part of the kernel was fucked for sure as even the hardware sleep button in my keyboard didn’t work but I guess if the display driver was functioning that would be all that was needed.

malfist 4y ago

I wonder why microsoft never implemented the Magic SysRq keys like linux: https://en.wikipedia.org/wiki/Magic_SysRq_key https://en.wikipedia.org/wiki/Magic_SysRq_key It'd let you safely shutdown when the computer is locked up otherwise.

kllrnohj 4y ago
The times my Linux installs have locked up, those keys never worked.
- malfist 4y ago
  They always worked for me, but it's been a long time since linux has locked up on me.
- pengaru 4y ago
  They may be disabled by distros to enhance security against physical access attacks. It can also be challenging to actually input a magic-sysrq combo on many modern keyboards where sysrq isn't its own key, if it's labeled at all as some Fn-key contortion.
  - nyanpasu64 4y ago
    Personally I value being able to trigger oomkiller early when a process is eating up RAM, and being able to SIGKILL kwin_x11 on Nvidia or whatever other process is wedging Linux shutdown, instead of waiting multiple minutes for systemd to give up waiting and SIGKILL it directly. In terms of physical access attacks, it's just as viable and far more powerful to add a keylogger to my keyboard or Linux distro, or pull and image my hard drive, than to gasp kill processes or sync filesystem data to disk, oh the horror!
    - pengaru 4y ago
      WRT the physical security argument in favor of disabling sysrq, my assumption is it's more aimed towards defeating quick-n-dirty mischief style abuse. Ages ago I worked with a small team of young sysadmins who would often cause trouble for one another abusing things like sysrq, or poorly configured XFree86 instances without DontZap enabled (ctrl-alt-backspace termination, to a shell when startx/xinit is being used). Most of the time nothing malicious was actually done. But when you return to your screen-locked X desktop to find a fullscreen VC with a root shell blinking back at you and an empty history, guess what you'll at least have on the back of your mind for the rest of the workday?

deleted 4y ago

[deleted]

robonerd 4y ago

> Especially helpful on a laptop where the physical reset button is not available. Are there any where holding the power button for 10-15 seconds doesn't work? This has always been a reliable technique for me, when using linux on numerous different laptops from different manufacturers.

Kwpolska 4y ago
Remote access?
- deleted 4y ago
  [deleted]
WorldMaker 4y ago
BIOS issues? Though Ctrl+Alt+Delete might not work with a BIOS acting up either.
kkfx 4y ago
That's ACPI shutdown, not OS-specific but motherboard specific AFAIK, it should work an all ACPI compliant systems...
- netsharc 4y ago
  Indeed. And afaik, the specs say hold it for 4 seconds
hulitu 4y ago
15 seconds migh be a lotof time, depending on the situation.