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Generate a grub.cfg that can boot Ubuntu ISO images.
Works with any Ubuntu ISO image that uses casper
(, which is every
desktop and live-server image.
Usage: -d path/to/directory/with/iso/images -o grub.cfg
import argparse
import os
import re
import sys
HEADER = """
# Notes for adding new entries:
# - run python3 -o grub.cfg
# Testing in KVM (assuming this USB drive is mounted as /dev/sdb1):
# - run sh kvmboot /dev/sdb1
# (if arrow keys don't work in the GRUB menu, use Ctrl-N/P)
'i386': 'x86',
'amd64': 'x86-64',
'desktop': 'desktop livecd',
'live-server': 'server livecd',
# if you wish to override a command line, or if the autodetection doesn't work,
# you can do it like this:
'ubuntu-16.04.6-server-amd64.iso': 'file=/cdrom/preseed/ubuntu-server.seed quiet ---',
# NB: this is pointless for ubuntu 16.04 LTS images, they're known not to work:
# they don't use casper, and debian-instaler doesn't know about iso-scan/filename=
# and so the installation fails a couple of steps in when it fails to find the .deb files
KVM_OK = "Tested in KVM, works"
KVM_DESKTOP_OK = "Tested in KVM, works (boots into live session)"
KVM_SERVER_OK = "Tested in KVM, works (boots, haven't tried to complete installation)"
# images I have tested personally
'ubuntu-20.04-desktop-amd64.iso': KVM_OK,
'ubuntu-20.04-live-server-amd64.iso': KVM_OK,
'ubuntu-20.04.1-desktop-amd64.iso': KVM_DESKTOP_OK,
'ubuntu-20.04.1-live-server-amd64.iso': KVM_SERVER_OK,
'ubuntu-19.10-desktop-amd64.iso': KVM_DESKTOP_OK,
'ubuntu-18.04.3-desktop-amd64.iso': KVM_DESKTOP_OK,
'ubuntu-18.04.4-desktop-amd64.iso': KVM_DESKTOP_OK,
'ubuntu-18.04.3-live-server-amd64.iso': KVM_OK,
'ubuntu-18.04.4-live-server-amd64.iso': KVM_OK,
'ubuntu-18.04.5-live-server-amd64.iso': KVM_SERVER_OK,
'ubuntu-16.04.6-desktop-i386.iso': KVM_DESKTOP_OK,
# and this is why overriding the command line can be futile, when autodetection doesn't work:
'ubuntu-16.04.6-server-amd64.iso': 'Does not work',
ENTRY = """
menuentry "{title}" {{
# {test_status}
set isofile="/ubuntu/{isofile}"
loopback loop $isofile
linux (loop){kernel} iso-scan/filename=$isofile {cmdline}
initrd (loop){initrd}
submenu "{title} >" {{
}} # end of submenu
FOOTER = """
menuentry "Memory test (memtest86+)" {
linux16 /boot/mt86plus
class Error(Exception):
def find_iso_files(where):
# We want to sort by Ubuntu version, in descending order, and then by image
# type, in ascending alphabetical order.
return sorted(
sorted(fn for fn in os.listdir(where) if fn.endswith('.iso')),
key=lambda fn: fn.split('-')[:2],
def group_files(files):
groups = []
current = []
current_prefix = None
for file in files:
prefix = file[:len('ubuntu-XX.YY')]
if prefix == current_prefix:
if len(current) == 1:
elif current:
current_prefix = prefix
current = [file]
if len(current) == 1:
elif current:
return groups
def make_grub_cfg(entries, isodir):
parts = [HEADER]
for entry_or_group in entries:
if isinstance(entry_or_group, list):
title = mkgrouptitle(entry_or_group)
parts.append(mksubmenu(title, [
mkentry(entry, isodir) for entry in entry_or_group
parts.append(mkentry(entry_or_group, isodir))
return ''.join(parts)
def mkgrouptitle(isofiles):
# ubuntu-XX.XX-variant-arch.iso
ubuntu, release, rest = isofiles[0].rpartition('.')[0].split('-', 2)
if is_lts(release):
release += ' LTS'
return f'Ubuntu {release}'
def mksubmenu(title, entries):
return SUBMENU.format(
def mkentry(isofile, isodir):
return ENTRY.format(
cmdline=mkcmdline(isofile, isodir),
initrd='/casper/initrd', # some older releases had initrd.gz
).replace('\n # \n', '\n') # remove empty comments
except Error as err:
print(f"skipping {isofile}: {err}", file=sys.stderr)
return ''
def mktitle(isofile):
# ubuntu-XX.XX-variant-arch.iso
ubuntu, release, rest = isofile.rpartition('.')[0].split('-', 2)
if ubuntu != 'ubuntu':
raise ValueError
variant, arch = rest.rsplit('-', 1)
if is_lts(release):
release += ' LTS'
except ValueError:
raise Error(f'filename does not look like ubuntu-XX.XX-variant-arch.iso')
return f'Ubuntu {release} ({ARCHS.get(arch, arch)} {VARIANTS.get(variant, variant)})'
def mkteststatus(isofile):
return '\n # '.join(get_test_status(isofile))
def get_test_status(isofile):
test_status = TEST_STATUS.get(isofile, 'Untested')
if not isinstance(test_status, list):
test_status = [test_status]
return test_status
def mkcmdline(isofile, isodir):
# too risky to guess
if isofile in KNOWN_COMMAND_LINES:
cmdline = KNOWN_COMMAND_LINES[isofile]
cmdline = extract_command_line_from_iso(os.path.join(isodir, isofile))
if isinstance(cmdline, dict):
cmdline = cmdline[None]
return cmdline
def extract_command_line_from_iso(isofile):
from parseiso import parse_iso, FormatError
with parse_iso(isofile) as walker:
grub_cfg ='/boot/grub/grub.cfg').decode('UTF-8', 'replace')
except (OSError, FormatError) as e:
raise Error(str(e))
return extract_command_line_from_grub_cfg(grub_cfg)
def extract_command_line_from_grub_cfg(grub_cfg_text):
rejected = []
for menuentry, linux, kernel, cmdline in extract_grub_menu(grub_cfg_text):
if (linux, kernel) == ('linux', '/casper/vmlinuz'):
return cmdline
rejected.append((menuentry, f"{linux} {kernel} {cmdline}"))
error = 'could not find a suitable kernel command line in grub.cfg inside the ISO image'
if rejected:
error += '\nrejected, because they use the wrong kernel (not /casper/vmlinuz):\n'
for menuentry, line in rejected:
error += f' menuentry "{menuentry}"\n {line}\n'
error += 'if you want to use one of these, edit and modify KNOWN_COMMAND_LINES'
raise Error(error)
def extract_grub_menu(grub_cfg_text):
menuentry_rx = re.compile(r'^\s*menuentry\s+"([^"]+)"')
linux_rx = re.compile(r'^\s*(linux|linux16)\s+(\S+)\s+(\S.*)')
menuentry = None
for line in grub_cfg_text.splitlines():
m = menuentry_rx.match(line)
if m:
menuentry =
m = linux_rx.match(line)
if m:
linux, kernel, cmdline = m.groups()
yield (menuentry, linux, kernel, cmdline)
def is_lts(release):
major, minor = map(int, release.split('.')[:2])
# 6.06 was the first LTS release; since then there's been an LTS every two
# years: 8.04, 10.04, 12.04, 14.04, 16.04, 18.04 and 20.04.
# we can ignore the past and focus on the current pattern.
return major % 2 == 0 and minor == 4
def print_groups(groups):
for group in groups:
if not isinstance(group, list):
group = [group]
print(f'# {mkgrouptitle(group)}')
for isofile in group:
width = 40
test_status = f'{" ":<{width}} # '.join(get_test_status(isofile))
print(f'{isofile:<{width}} # {test_status}')
def main():
parser = argparse.ArgumentParser(description="create a grub.cfg for Ubuntu ISO images")
parser.add_argument("--list", action='store_true', help='list found ISO images')
parser.add_argument("-d", "--iso-dir", metavar='DIR', default="../../ubuntu",
help="directory with ISO images (default: %(default)s)")
parser.add_argument("-o", metavar='FILENAME', dest='outfile', default="-",
help="write the generated grub.cfg to this file (default: stdout)")
args = parser.parse_args()
iso_files = find_iso_files(args.iso_dir)
groups = group_files(iso_files)
if args.list:
grub_cfg = make_grub_cfg(groups, args.iso_dir)
if args.outfile != '-':
with open(args.outfile, 'w') as f:
print(grub_cfg, end="")
except Error as e:
if __name__ == "__main__":