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What is the difference between the two? In a Linux 2.6.x kernel.

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If you are kernel development you could have sudden kernel panic, SysRq key will be very valuable. The magic SysRq key is a key combination in the Linux kernel which allows the user to perform various low level commands regardless of the system’s state.

normally when you do Alt+SysRQ+b system reboots without umounting or sync

This command is often used to recover from freezes, or to reboot a computer without affecting the current file system.

Enabling SysRq is much similar to attempting reset button physically on server.

No daemons will be shut down gracefully, no filesystem sync will occur, but you may get the wrath of a fsck (or worse, a non-booting server) upon reboot.

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  • Understood thanks. How does this differ from pressing the reset switch on a server or issuing a reset via the drac/system management bus? Commented Mar 14, 2016 at 16:52
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    The physical reset switch effectively kills the power to hardware devices momentarily. Using magic SysRq to reboot is in effect still entirely in software. As such, if the integrated electronics on your hard drive are still executing a cached write to the medium, a hard reset will interrupt this, virtually guaranteeing data corruption. A reset through Magic SysRq is less likely to have this side-effect.
    – DopeGhoti
    Commented Mar 14, 2016 at 18:07

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