fill_fstab.py

import argparse
import subprocess
import sys
import os


def run_cmd(cmd, check=True):
    """
    Helper to run a command using subprocess.
    If check=True, raises an exception on nonzero return.
    """
    print(f"[CMD] {' '.join(cmd)}")
    subprocess.run(cmd, check=check)


def get_uuid(device):
    """
    Retrieve the UUID of a device using blkid.
    """

    result = subprocess.run(
        ["blkid", "-s", "UUID", "-o", "value", device],
        capture_output=True,
        text=True,
        check=True,
    )
    return result.stdout.strip()


def append_fstab_entries(mount_path, device_uuid):
    """
    Append btrfs subvolume entries and swapfile entry to /mnt/etc/fstab
    """

    etc_dir = os.path.join(mount_path, "etc")
    os.makedirs(etc_dir, exist_ok=True)

    fstab_path = os.path.join(etc_dir, "fstab")

    # We assume user wants stadnard default mounts
    # We may want to add other options like

    fstab_entries = f"""
    # BTRFS subvolume mounts
    UUID={device_uuid}      /               btrfs defaults,subvol=@                 0 0
    UUID={device_uuid}      /boot           btrfs defaults,subvol=@boot             0 0
    UUID={device_uuid}      /swap           btrfs defaults,subvol=@swap             0 0
    UUID={device_uuid}      /snapshots      btrfs defaults,subvol=@snapshots        0 0
    UUID={device_uuid}      /var            btrfs defaults,subvol=@var              0 0
    UUID={device_uuid}      /home           btrfs defaults,subvol=@home             0 0
    UUID={device_uuid}      /tmp            btrfs defaults,subvol=@tmp              0 0

    # Swap file
    /swap/swapfile          none            swap    sw                              0 0

    """

    print("Appending the following to /mnt/etc/fstab:\n")
    print(fstab_entries)

    with open(fstab_path, "a") as f:
        f.write(fstab_entries)


def main():
    parser = argparse.ArgumentParser(
        description="Get the UUID of the device and append to /etc/fstab."
    )

    parser.add_argument(
        "--device", required=True, help="Path to the partition (e.g. /dev/nvme0n1p1)."
    )
    args = parser.parse_args()

    device = args.device

    print("Retrieving UUID of the device & Updating fstab entries...")
    device_uuid = get_uuid(device)
    append_fstab_entries("/mnt", device_uuid)


if __name__ == "__main__":
    if os.geteuid() != 0:
        print("This script must be run as root (sudo). Exiting.")
        sys.exit(1)
    main()