ironic/install-guide/source/include/kernel-boot-parameters.rst

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 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:

#!/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')