How to use grub2-extra-lua module

Question

I googled for grub2-lua, but found very few information on it. I can't find an official website for grub2-lua (i.e official source code tarball download link), except for a git clone link.

Moreover, I can't find any documentation about grub lua. So I don't know how to use it.

I managed to compile grub2 along with lua module, then I boot into grub and type "help lua" to try to get some help info. But it only says that I can use command "lua script_file.lua" to execute the lua script. So I just want to learn the details on how to use lua module. For example, how to execute lua commands in grub.cfg file, how to return the lua execution result to the grub.cfg file, and what APIs does grub provide to the lua module.

The reason why I use lua module is that I have the need of file system operations in grub (i.e. mv, cp, cd, pwd, mkdir, rm, nano commands). grub2 itself doesn't provide this functionality. Some posts said grub-extra-lua module may provide this feature.

So I just want to know how to use grub lua module to operate on files and directories.

Answer 1

I found a blog about using grub2-lua http://linux.xvx.cz/2010/03/using-grub2-and-lua-installed-on-usb.html

it seems to me you could load the lua script directly from grub.cfg by adding

insmod vbe (or insmod vbeinfo)

# Uncomment for a different ISO files search path
#set isofolder="/boot/isos"
#export isofolder

# Uncomment for a different live system language
#set isolangcode="us"
#export isolangcode

lua /boot/grub/bootiso.lua

i copied the bootiso.lua script here. which is for automatically booting ISO images with changing versions/filenames

#!lua
-- Detects the live system type and boots it
function boot_iso (isofile, langcode)
  -- grml
  if (dir_exist ("(loop)/boot/grml64")) then
    boot_linux (
      "(loop)/boot/grml64/linux26",
      "(loop)/boot/grml64/initrd.gz",
      "findiso=" .. isofile .. " apm=power-off quiet boot=live nomce"
    )
  -- Parted Magic
  elseif (dir_exist ("(loop)/pmagic")) then
    boot_linux (
      "(loop)/pmagic/bzImage",
      "(loop)/pmagic/initramfs",
      "iso_filename=" .. isofile ..
        " edd=off noapic load_ramdisk=1 prompt_ramdisk=0 rw" ..
        " sleep=10 loglevel=0 keymap=" .. langcode
    )
  -- Sidux
  elseif (dir_exist ("(loop)/sidux")) then
    boot_linux (
      find_file ("(loop)/boot", "vmlinuz%-.*%-sidux%-.*"),
      find_file ("(loop)/boot", "initrd%.img%-.*%-sidux%-.*"),
      "fromiso=" .. isofile .. " boot=fll quiet"
    )
  -- Slax
  elseif (dir_exist ("(loop)/slax")) then
    boot_linux (
      "(loop)/boot/vmlinuz",
      "(loop)/boot/initrd.gz",
      "from=" .. isofile .. " ramdisk_size=6666 root=/dev/ram0 rw"
    )
  -- SystemRescueCd
  elseif (grub.file_exist ("(loop)/isolinux/rescue64")) then
    boot_linux (
      "(loop)/isolinux/rescue64",
      "(loop)/isolinux/initram.igz",
      "isoloop=" .. isofile .. " docache rootpass=xxxx setkmap=" .. langcode
    )
  -- Tinycore
  elseif (grub.file_exist ("(loop)/boot/tinycore.gz")) then
    boot_linux (
      "(loop)/boot/bzImage",
      "(loop)/boot/tinycore.gz"
    )
  -- Ubuntu and Casper based Distros
  elseif (dir_exist ("(loop)/casper")) then
    boot_linux (
      "(loop)/casper/vmlinuz",
      find_file ("(loop)/casper", "initrd%..z"),
      "boot=casper iso-scan/filename=" .. isofile ..
        " quiet splash noprompt" ..
        " keyb=" .. langcode ..
        " debian-installer/language=" .. langcode ..
        " console-setup/layoutcode?=" .. langcode ..
        " --"
    )
  -- Xpud
  elseif (grub.file_exist ("(loop)/boot/xpud")) then
    boot_linux (
      "(loop)/boot/xpud",
      "(loop)/opt/media"
    )
  else
    print_error ("Unsupported ISO type")
  end
end
-- Help function to show an error
function print_error (msg)
  print ("Error: " .. msg)
  grub.run ("read")
end
-- Help function to search for a file
function find_file (folder, match)
  local filename
  local function enum_file (name)
    if (filename == nil) then
      filename = string.match (name, match)
    end
  end
  grub.enum_file (enum_file, folder)
  if (filename) then
    return folder .. "/" .. filename
  else
    return nil
  end
end
-- Help function to check if a directory exist
function dir_exist (dir)
  return (grub.run("test -d '" .. dir .. "'") == 0)
end
-- Boots a Linux live system
function boot_linux (linux, initrd, params)
  if (linux and grub.file_exist (linux)) then
    if (initrd and grub.file_exist (initrd)) then
      if (params) then
        grub.run ("linux " .. linux .. " " .. params)
      else
        grub.run ("linux " .. linux)
      end
      grub.run ("initrd " .. initrd)
    else
      print_error ("Booting Linux failed: cannot find initrd file '" .. initrd .. "'")
    end
  else
    print_error ("Booting Linux failed: cannot find linux file '" .. initrd .. "'")
  end
end
-- Mounts the iso file
function mount_iso (isofile)
  local result = false
  if (isofile == nil) then
    print_error ("variable 'isofile' is undefined")
  elseif (not grub.file_exist (isofile)) then
    print_error ("Cannot find isofile '" .. isofile .. "'")
  else
    local err_no, err_msg = grub.run ("loopback loop " .. isofile)
    if (err_no ~= 0) then
      print_error ("Cannot load ISO: " .. err_msg)
    else
      result = true
    end
  end
  return result
end
-- Getting the environment parameters
isofile = grub.getenv ("isofile")
langcode = grub.getenv ("isolangcode")
if (langcode == nil) then
  langcode = "us"
end
-- Mounting and booting the live system
if (mount_iso (isofile)) then
  boot_iso (isofile, langcode)
end