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+Linux:Manual Restart with sysrq-trigger
+=======================================
+:author: Aaron Ball
+:email: nullspoon@oper.io
+:revdate: February 15, 2016
+
+
+== {doctitle}
+
+A little over a week ago I decided it would be fun to try to write my own
+multi-threaded init system in c. Without going into too much detail (I'll write
+a blog post that introduces it once it's further along), I needed to find a way
+to shutdown and restart my system from c (init 0 and 6, respectively).
+
+I looked around the internet and had a surprisingly difficult time finding what
+I was looking for. Every post I found indicated I should use the system
+function to call "shutdown -h -P now". While not a wrong or a bad answer, it
+wasn't the answer I was looking for. I wanted to know how the shutdown and
+reboot commands worked, or how my current init system executed runlevels 0 and
+6, respectively.
+
+Remembering something I found a ways back about kernel triggers found in and
+/sys/power/ for controlling acpi states, I started searching for something
+similar. After a bit of time, I found */proc/sysrq-trigger*. For further
+reading beyond this post, please see the
+https://en.wikipedia.org/wiki/Magic_SysRq_key[Wikipedia Article].
+
+
+
+Simple Usage
+------------
+
+The usage of sysrq-trigger is fairly simple. Before we get into exact usage for
+the purposes of shutting down or rebooting though, please note that output from
+/proc/sysrq-trigger can only be seen from an actual tty, and not from within a
+terminal emulator.
+
+That said, execute the following command to find out all of the options
+available to you from sysrq.
+
+    # echo h > /proc/sysrq-trigger
+
+If you don't see output from that, either sysrq isn't enabled, or you aren't
+executing from within a tty.
+
+To check if it is enabled, ensure that the following command yields a *1*.
+
+    # cat /proc/sys/kernel/sysrq
+
+
+
+Reboot and Shutdown Sequences
+-----------------------------
+
+If you executed the _echo h_ statement above, you likely saw the output of
+supported commands. Among them you should havE seen *b* and *o*, for reboot and
+poweroff, respectively. _Note that it is a bad idea to execute either of these
+right now._
+
+If you read around the internet for what these two do, you'll see that both
+cause a hard stop. Neither polietly asks processes to exit. They are roughly
+equivelant to the hardware reset and power buttons. If rebooting or powering
+off, *we want b or o to be the last command sent* to have as graceful a stop as
+possible.
+
+
+Here is the list of commands that should be sent to sysrq-trigger, in order,
+for both a shutdown and a reboot.
+
+echo r > /proc/sysrq-trigger:: (un*R*aw) Takes back control of keyboard from X
+
+echo e > /proc/sysrq-trigger:: (t*E*rminate) Send SIGTERM to all processes. If
+                               you aren't familiar with process signals, this
+                               is basically a friendly kill command for every
+                               process.
+
+echo i > /proc/sysrq-trigger:: (k*I*ll) Send SIGKILL to all processes. If you
+                               aren't familiar with process signals, this is
+                               basically a kill -9 command for every remaining
+                               process.
+
+echo s > /proc/sysrq-trigger:: (*S*nc) Sync all cached disk operations to disk
+
+echo u > /proc/sysrq-trigger:: (*U*mount) Umounts all mounted partitions
+
+
+The previous commands all get us to a ready to shutdown or reboot state. To
+shutdown or reboot, execute one of the following.
+
+echo o > /proc/sysrq-trigger:: (p*O*weroff) Powers off the system
+
+echo b > /proc/sysrq-trigger:: (re*B*oot) Reboots the system
+
+
+The entire list in order, using the reboot command...
+
+    # echo r > /proc/sysrq-trigger
+    # echo e > /proc/sysrq-trigger
+    # echo i > /proc/sysrq-trigger
+    # echo s > /proc/sysrq-trigger
+    # echo u > /proc/sysrq-trigger
+    # echo b > /proc/sysrq-trigger
+
+
+[role="datelastedit"]
+Last edited: {revdate}
+// vim: set syntax=asciidoc: