Add a doc about appending kernel parameters to boot instances

Close-Bug: #1569189
Change-Id: I3395e635a5c4f45e00ee809dceb63c1755b9e66a

doc/source/deploy/install-guide.rst

@@ -2298,6 +2298,72 @@ but in order to use it we should follow some rules:
 
 .. _`expected format`: http://docs.openstack.org/user-guide/cli_config_drive.html#openstack-metadata-format
 
+
+Appending kernel parameters to boot instances
+=============================================
+
+The Bare Metal service supports passing custom kernel parameters to boot instances to fit
+users' requirements. The way to append the kernel parameters is depending on how to boot instances.
+
+Network boot
+------------
+Currently, the Bare Metal service supports assigning unified kernel parameters to PXE
+booted instances by:
+
+* Modifying the ``[pxe]/pxe_append_params`` configuration option, for example::
+
+    [pxe]
+
+    pxe_append_params = quiet splash
+
+* Copying a template from shipped templates to another place, for example::
+
+    https://git.openstack.org/cgit/openstack/ironic/tree/ironic/drivers/modules/pxe_config.template
+
+  Making the modifications and pointing to the custom template via the configuration
+  options: ``[pxe]/pxe_config_template`` and ``[pxe]/uefi_pxe_config_template``.
+
+Local boot
+----------
+For local boot instances, users can make use of configuration drive
+(see `Enabling the configuration drive (configdrive)`_) to pass a custom
+script to append kernel parameters when creating an instance. This is more
+flexible and can vary per instance.
+Here is an example for grub2 with ubuntu, users can customize it
+to fit their use case:
+
+    .. code:: python
+
+     #!/usr/bin/env python
+     import os
+
+     # Default grub2 config file in Ubuntu
+     grub_file = '/etc/default/grub'
+     # Add parameters here to pass to instance.
+     kernel_parameters = ['quiet', 'splash']
+     grub_cmd = 'GRUB_CMDLINE_LINUX'
+     old_grub_file = grub_file+'~'
+     os.rename(grub_file, old_grub_file)
+     cmdline_existed = False
+     with open(grub_file, 'w') as writer, \
+            open(old_grub_file, 'r') as reader:
+            for line in reader:
+                key = line.split('=')[0]
+                if key == grub_cmd:
+                    #If there is already some value:
+                    if line.strip()[-1] == '"':
+                        line = line.strip()[:-1] + ' ' + ' '.join(kernel_parameters) + '"'
+                    cmdline_existed = True
+                writer.write(line)
+            if not cmdline_existed:
+                line = grub_cmd + '=' + '"' + ' '.join(kernel_parameters) + '"'
+                writer.write(line)
+
+     os.remove(old_grub_file)
+     os.system('update-grub')
+     os.system('reboot')
+
+
 .. _BuildingDeployRamdisk:
 
 Building or downloading a deploy ramdisk image