Merge pull request #34 from rebortg/add/bootsteps

add boot steps

docs/troubleshooting.rst

@@ -297,8 +297,45 @@ to clear counters on firewall rulesets or single rules
   vyos@vyos:~$ clear firewall ipv6-name <ipv6 ruleset name> counters
   vyos@vyos:~$ clear firewall ipv6-name <ipv6 ruleset name> rule <rule#> counters
 
-  
 
+Basic System Information
+------------------------
+
+Boot steps
+^^^^^^^^^^
+
+VyOS 1.2.0+ uses `Debian Jessie`_ as the base Linux operating system.
+Jessie was the first version of Debian that uses `systemd`_ as the default init system.
+
+These are the boot steps for VyOS 1.2.0+
+
+1. The BIOS loads Grub (or isolinux for the Live CD)
+2. Grub then starts the Linux boot and loads the Linux Kernel ``/boot/vmlinuz``
+3. Kernel Launches Systemd ``/lib/systemd/systemd``
+4. Systemd loads the VyOS service file ``/lib/systemd/system/vyos-router.service``
+5. The service file launches the VyOS router init script ``/usr/libexec/vyos/init/vyos-router`` - this is part of the `vyatta-cfg`_ Debian package
+
+  1. Starts FRR_ - successor to `GNU Zebra`_ and `Quagga`_
+
+  2. Initialises the boot configuration file - copies over ``config.boot.default`` if there is no configuration
+  3. Runs the configuration migration, if the configuration is for an older version of VyOS
+  4. Runs The pre-config script, if there is one ``/config/scripts/vyos-preconfig-bootup.script``
+  5. If the config file was upgraded, runs any post upgrade scripts ``/config/scripts/post-upgrade.d``
+  6. Starts **rl-system** and **firewall**
+  7. Mounts the ``/boot`` partition
+  8. The boot configuration file is then applied by ``/opt/vyatta/sbin/vyatta-boot-config-loader /opt/vyatta/etc/config/config.boot``
+
+    1. The config loader script writes log entries to ``/var/log/vyatta-config-loader.log``
+
+  10. Runs ``telinit q`` to tell the init system to reload ``/etc/inittab``
+  11. Finally it runs the post-config script ``/config/scripts/vyos-postconfig-bootup.script``
+
+.. _Quagga: http://www.quagga.net/
+.. _`GNU Zebra`: https://www.gnu.org/software/zebra/
+.. _FRR: https://frrouting.org/
+.. _vyatta-cfg: https://github.com/vyos/vyatta-cfg
+.. _systemd: _https://freedesktop.org/wiki/Software/systemd/
+.. _`Debian Jessie`: https://www.debian.org/releases/jessie/
 .. _mtr: http://www.bitwizard.nl/mtr/
 .. _tshark: https://www.wireshark.org/docs/man-pages/tshark.html
 .. _`PCAP filter expressions`: http://www.tcpdump.org/manpages/pcap-filter.7.html