Raising Elephants Is So Utterly Boring

You Linux stooped. Ctrl+Alt+Backspace does nothing, And f-keys dont respond . You installed wrong driver or overflow memory don wory Remember quote

Raising Elephants Is So Utterly Boring”, “Reboot Even If System Utterly Broken

This is very old magic spell  give you control when another lost hope REISUB


What is SysRq

It is a ‘magical’ key combo you can hit which the kernel will respond to
regardless of whatever else it is doing, unless it is completely locked up.(*1)


First step check we need check how many sysqrt is aceptablem in you system

cat /proc/sys/kernel/sysrq

Sys commands required configure in compilation process CONFIG_MAGIC_SYSRQ most part of linux system have right configure this.

How to use magic SysRq
x86 : ALT+SysRq + <command key>
Sparc: ALT+STOP +<command key>
by ssh: echo <command key> > /proc/sysrq-trigger

Char Action
‘b’ Will immediately reboot the system without syncing or unmounting your disks.
‘c’ Will perform a system crash by a NULL pointer dereference.A crashdump will be taken if configured.
‘d’ Shows all locks that are held.
‘e’ Send a SIGTERM to all processes, except for init.
‘f’ Will call the oom killer to kill a memory hog process, but do notpanic if nothing can be killed.
‘g’ Used by kgdb (kernel debugger)
‘h’ Will display help (actually any other key than those listed here will display help. but ‘h’ is easy to remember 🙂
‘i’ Send a SIGKILL to all processes, except for init.
‘j’ Forcibly “Just thaw it” – filesystems frozen by the FIFREEZE ioctl.
‘k’ Secure Access Key (SAK) Kills all programs on the current virtual console. NOTE: See important comments below in SAK section.
‘l’ Shows a stack backtrace for all active CPUs.
‘m’ Will dump current memory info to your console.
‘n’ Used to make RT tasks nice-able
‘o’ Will shut your system off (if configured and supported).
‘p’ Will dump the current registers and flags to your console.
‘q’ Will dump per CPU lists of all armed hrtimers (but NOT regular timer_list timers) and detailed information about all clockevent devices.
‘r’ Turns off keyboard raw mode and sets it to XLATE.
‘s’ Will attempt to sync all mounted filesystems.
‘t’ Will dump a list of current tasks and their information to your console.
‘u’ Will attempt to remount all mounted filesystems read-only.
‘v’ Forcefully restores framebuffer console
‘v’ Causes ETM buffer dump [ARM-specific]
‘w’ Dumps tasks that are in uninterruptable (blocked) state.
‘x’ Used by xmon interface on ppc/powerpc platforms. Show global PMU Registers on sparc64. Dump all TLB entries on MIPS.
‘y’ Show global CPU Registers [SPARC-64 specific]
‘z’ Dump the ftrace buffer
‘0’-‘9’ Sets the console log level, controlling which kernel messages will be printed to your console. (‘0’, for example would make It so that only emergency messages like PANICs or OOPSes would make it to your console.)

More about sysrq


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