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Add --grab-reboot option to trigger system reboot via keyboard shortcut#176

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kdj0c merged 3 commits intokmscon:mainfrom
jtollet:feature/grab-reboot
Dec 17, 2025
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Add --grab-reboot option to trigger system reboot via keyboard shortcut#176
kdj0c merged 3 commits intokmscon:mainfrom
jtollet:feature/grab-reboot

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@jtollet
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@jtollet jtollet commented Dec 13, 2025 •
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Summary

This PR adds a new --grab-reboot option that allows users to configure a keyboard shortcut to reboot the system directly from kmscon.

Features

  • Disabled by default: Users must explicitly configure a key combination
  • Direct system call: Uses reboot(RB_AUTOBOOT) for reliability
  • Configurable: Supports any key combination (e.g., <Ctrl><Alt>Delete)

Implementation

  • Added grab_reboot field to kmscon_conf_t configuration structure
  • Implemented seat_trigger_reboot() function using reboot(RB_AUTOBOOT)
  • Integrated into seat-level input event handling in seat_input_event()
  • Updated kmscon.1.xml.in and kmscon.conf.1.xml.in man pages

Usage

# Command line
kmscon --grab-reboot='<Ctrl><Alt>Delete'

# Configuration file
grab-reboot=<Ctrl><Alt>Delete

Modified Files

  • src/kmscon_conf.h - Configuration structure
  • src/kmscon_conf.c - Option definition and help text
  • src/kmscon_seat.c - Reboot trigger implementation
  • docs/man/kmscon.1.xml.in - Command-line option documentation
  • docs/man/kmscon.conf.1.xml.in - Configuration file documentation

@jtollet jtollet force-pushed the feature/grab-reboot branch from 373f8ea to 23f6c8e Compare December 13, 2025 17:37
michael-oberpriller
michael-oberpriller reviewed Dec 14, 2025
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@jtollet
Add --grab-reboot option to trigger system reboot via keyboard shortcut
e0d135a 
This commit adds a new configurable keyboard shortcut option --grab-reboot
that allows users to reboot the system directly from kmscon.

Features:
- Disabled by default (user must explicitly configure a key combination)
- Uses direct reboot() system call for reliability
- Calls sync() before reboot to ensure data safety
- Independent of --session-control flag
- Fully configurable key combination (e.g., <Ctrl><Alt>Delete)
- Includes comprehensive documentation in man pages

Implementation details:
- Added grab_reboot field to kmscon_conf_t structure
- Added seat_trigger_reboot() function using reboot(RB_AUTOBOOT)
- Integrated into seat-level input event handling
- Updated both kmscon.1 and kmscon.conf.1 man pages

Usage example:
  kmscon --grab-reboot='<Ctrl><Alt>Delete'
@jtollet jtollet force-pushed the feature/grab-reboot branch from 23f6c8e to e0d135a Compare December 14, 2025 07:16
@kdj0c
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kdj0c commented Dec 14, 2025

I'm a bit skeptical about this feature, but the code looks good, and it doesn't introduce complexity, so if no other comments I will merge it soon.

@jtollet
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jtollet commented Dec 14, 2025 via email

@jtollet
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jtollet commented Dec 14, 2025 via email

@kdj0c kdj0c merged commit 9f9a8ec into kmscon:main Dec 17, 2025
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@kdj0c kdj0c mentioned this pull request Jan 2, 2026
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@satmandu
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satmandu commented Jan 7, 2026

Thanks for this! I was just complaining to myself about ctrl-alt-del not being capable of rebooting my machine this morning.

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jtollet commented Jan 7, 2026 •
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@satmandu that quite common... And that's why linux vt supports it too. TY !

@Karlson2k
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Karlson2k commented Jan 24, 2026

Cool!
I was missing this really useful feature.

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Karlson2k commented Jan 28, 2026

While the feature is very useful, this implementation is quite dangerous.
With this implementation, a syscall (via a libc wrapper) is called to perform the reboot directly.
In contrast, when Ctrl-Alt-Del is pressed in the Linux console, SIGINT is sent to PID 1, and then the init process performs a clean reboot.
I think people who are using this feature are expecting the same behaviour as with the standard Linux console, and they can be surprised by data loss or a damaged filesystem due to an unclean shutdown.

I suggest either replacing this hard reboot with a proper SIGINT to PID 1, or at least making this configurable.
In the meantime, a BIG FAT warning could be added to the configuration example to avoid unpleasant surprises for users.

@Karlson2k Karlson2k mentioned this pull request Jan 28, 2026
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jtollet added a commit to jtollet/kmscon that referenced this pull request Jan 28, 2026
@jtollet
docs: Add warnings about hard reboot mode and clarify soft mode behavior
2bf9401 
Following Karlson2k's feedback on PR kmscon#176, this commit adds clear warnings
about the dangers of "hard" mode (immediate reboot without proper shutdown)
which can cause data loss and filesystem corruption.

The documentation now explicitly states that:
- "soft" mode (default) sends SIGINT to PID 1 for a clean reboot,
  matching the standard Linux console Ctrl-Alt-Del behavior
- "hard" mode performs an immediate reboot via reboot(RB_AUTOBOOT)
  with sync() but without proper shutdown sequence

Changes:
- Updated man pages (kmscon.1 and kmscon.conf.1) with detailed warnings
- Updated kmscon.conf.example with prominent DATA LOSS warning
- Clarified that soft mode matches Linux console behavior users expect

Tested on real hardware with both modes:
- soft mode: clean shutdown via SIGINT to PID 1 ✓
- hard mode: immediate reboot via RB_AUTOBOOT ✓
jtollet added a commit to jtollet/kmscon that referenced this pull request Jan 28, 2026
@jtollet
docs: Add warnings about hard reboot mode and clarify soft mode behavior
89637d5 
Following Karlson2k's feedback on PR kmscon#176, this commit adds clear warnings
about the dangers of "hard" mode (immediate reboot without proper shutdown)
which can cause data loss and filesystem corruption.

The documentation now explicitly states that:
- "soft" mode (default) sends SIGINT to PID 1 for a clean reboot,
  matching the standard Linux console Ctrl-Alt-Del behavior
- "hard" mode performs an immediate reboot via reboot(RB_AUTOBOOT)
  with sync() but without proper shutdown sequence

Changes:
- Updated man pages (kmscon.1 and kmscon.conf.1) with detailed warnings
- Updated kmscon.conf.example with prominent DATA LOSS warning
- Clarified that soft mode matches Linux console behavior users expect

Tested on real hardware with both modes:
- soft mode: clean shutdown via SIGINT to PID 1 ✓
- hard mode: immediate reboot via RB_AUTOBOOT ✓
@jtollet jtollet mentioned this pull request Jan 28, 2026
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@jtollet
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jtollet commented Jan 28, 2026

@Karlson2k Thank you for the excellent feedback!

You're absolutely right about the concerns with hard reboot. I've addressed all your suggestions in PR #260:

What was implemented:

  • SIGINT to PID 1 (soft mode) is now the default behavior, matching the standard Linux console Ctrl-Alt-Del
  • Hard mode is optional via --grab-reboot-mode=hard
  • BIG FAT warnings added to all documentation (man pages and config example) about data loss and filesystem corruption risks with hard mode
  • Clear documentation that soft mode matches what users expect from the Linux console

Testing:
Both modes have been tested on real hardware:

  • ✅ Soft mode: clean shutdown via SIGINT to PID 1 (default)
  • ✅ Hard mode: sync() + immediate reboot via RB_AUTOBOOT (optional, with warnings)

The implementation follows your recommendation to make this configurable while defaulting to the safe behavior users expect.

See PR #260 for the documentation updates: #260

@jtollet
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jtollet commented Jan 28, 2026

@Karlson2k Thank you for the excellent feedback!

You're absolutely right about the concerns with hard reboot. I've addressed all your suggestions in PR #260:

What was implemented:

  • SIGINT to PID 1 (soft mode) is now the default behavior, matching the standard Linux console Ctrl-Alt-Del
  • Hard mode is optional via --grab-reboot-mode=hard
  • BIG FAT warnings added to all documentation (man pages and config example) about data loss and filesystem corruption risks with hard mode
  • Clear documentation that soft mode matches what users expect from the Linux console

About hard mode:
Even in hard mode, sync() is called before reboot(RB_AUTOBOOT) to flush disk buffers. However, this doesn't prevent potential data loss since the system doesn't perform proper shutdown of services, unmounting filesystems, etc. This is why we added prominent warnings.

Testing:
Both modes have been tested on real hardware:

  • ✅ Soft mode: clean shutdown via SIGINT to PID 1 (default)
  • ✅ Hard mode: sync() + immediate reboot via RB_AUTOBOOT (optional, with warnings)

The implementation follows your recommendation to make this configurable while defaulting to the safe behavior users expect.

See PR #260 for the documentation updates: #260

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