Archive for March, 2016

Using Linux SysRq

On x86   - You press the key combo 'ALT-SysRq-<command key>'. Note - Some
           keyboards may not have a key labeled 'SysRq'. The 'SysRq' key is
           also known as the 'Print Screen' key. Also some keyboards cannot
	   handle so many keys being pressed at the same time, so you might
	   have better luck with "press Alt", "press SysRq", "release SysRq",
	   "press <command key>", release everything.

*  What are the 'command' keys?
'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 not
	  panic 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

'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 info :

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