Customization in a /etc/defaults/grub when using grub2

[mdujava]

When I try to use predefined config + credentials file, I do not see a way how to customize grub or (mkinicpio) to include lvm2 and set serial for grub+kernel.

I need to update /etc/default/grub with:

GRUB_CMDLINE_LINUX_DEFAULT="... console=ttyS0,115200n8"
GRUB_TERMINAL_INPUT=serial
GRUB_TERMINAL_OUTPUT=serial
GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1"

before grub-mkconfig is run, is there a way how to update the config.json to do it automated?

using: configuration.json:

{
    "app_config": {},
    "archinstall_language": "English",
    "auth_config": {},
    "bootloader_config": {
        "bootloader": "Grub",
        "removable": false,
        "uki": false
    },
    "custom_commands": [],
    "disk_config": {
        "btrfs_options": {
            "snapshot_config": null
        },
        "config_type": "default_layout",
        "device_modifications": [
            {
                "device": "/dev/sda",
                "partitions": [
                    {
                        "btrfs": [],
                        "dev_path": null,
                        "flags": [
                            "boot"
                        ],
                        "fs_type": "fat32",
                        "mount_options": [],
                        "mountpoint": "/boot",
                        "obj_id": "7072658d-e36d-4fe5-b469-61b1f96bc118",
                        "size": {
                            "sector_size": {
                                "unit": "B",
                                "value": 512
                            },
                            "unit": "B",
                            "value": 830472192
                        },
                        "start": {
                            "sector_size": {
                                "unit": "B",
                                "value": 512
                            },
                            "unit": "MiB",
                            "value": 1
                        },
                        "status": "create",
                        "type": "primary"
                    },
                    {
                        "btrfs": [],
                        "dev_path": null,
                        "flags": [],
                        "fs_type": "ext4",
                        "mount_options": [],
                        "mountpoint": "/",
                        "obj_id": "88d58ae8-37b5-4440-a123-7f193a10c395",
                        "size": {
                            "sector_size": {
                                "unit": "B",
                                "value": 512
                            },
                            "unit": "B",
                            "value": 5608833024
                        },
                        "start": {
                            "sector_size": {
                                "unit": "B",
                                "value": 512
                            },
                            "unit": "B",
                            "value": 831520768
                        },
                        "status": "create",
                        "type": "primary"
                    }
                ],
                "wipe": true
            }
        ],
        "lvm_config": {
            "config_type": "default",
            "vol_groups": [
                {
                    "lvm_pvs": [
                        "88d58ae8-37b5-4440-a123-7f193a10c395"
                    ],
                    "name": "arch26vg",
                    "volumes": [
                        {
                            "btrfs": [],
                            "fs_type": "ext4",
                            "length": {
                                "sector_size": {
                                    "unit": "B",
                                    "value": 512
                                },
                                "unit": "MiB",
                                "value": 4608
                            },
                            "mount_options": [],
                            "mountpoint": "/",
                            "name": "root",
                            "obj_id": "e242042d-086f-42ea-8779-23521044f23b",
                            "status": "create"
                        },
                        {
                            "btrfs": [],
                            "fs_type": "linux-swap",
                            "length": {
                                "sector_size": {
                                    "unit": "B",
                                    "value": 512
                                },
                                "unit": "MiB",
                                "value": 660
                            },
                            "mount_options": [],
                            "mountpoint": null,
                            "name": "swap",
                            "obj_id": "34035106-75ba-4502-b023-d684d6b84131",
                            "status": "create"
                        }
                    ]
                }
            ]
        }
    },
    "hostname": "fast-vm-arch",
    "kernels": [
        "linux"
    ],
    "locale_config": {
        "console_font": "default8x16",
        "kb_layout": "us",
        "sys_enc": "UTF-8",
        "sys_lang": "en_US.UTF-8"
    },
    "mirror_config": {
        "custom_repositories": [],
        "custom_servers": [],
        "mirror_regions": {},
        "optional_repositories": []
    },
    "network_config": {
        "type": "manual"
    },
    "ntp": false,
    "packages": ["lvm2"],
    "pacman_config": {
        "color": true,
        "parallel_downloads": 5
    },
    "profile_config": {
        "gfx_driver": null,
        "greeter": null,
        "profile": {
            "custom_settings": {
                "sshd": {}
            },
            "details": [
                "sshd"
            ],
            "main": "Server"
        }
    },
    "script": null,
    "services": [],
    "swap": {
        "algorithm": "zstd",
        "enabled": true
    },
    "timezone": "Europe/London",
    "version": "4.4"
}

[h8d13]

LVM im pretty sure you do not even need to add to packages as it will get added auto

For grub specifically you'll likely want to add to this def (or use plugins but im not familiar with that)

archinstall/archinstall/lib/installer.py

Line 1327 in e24af61

def _add_grub_bootloader(