/lib/partman/update.d/21biosgrub_sync_flag is in ubiquity 18.04.14.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 | #! /bin/sh
# Remove the bios_grub flag for partitions whose method is not biosgrub, and
# set it for partitions whose method is biosgrub.
. /lib/partman/lib/base.sh
dev=$1
num=$2
id=$3
size=$4
type=$5
fs=$6
path=$7
name=$8
cd $dev
if [ "$fs" = free ]; then
exit 0
fi
method=
if [ -f "$id/method" ]; then
method="$(cat "$id/method")"
fi
has_biosgrub=no
flags=''
open_dialog GET_FLAGS "$id"
while { read_line flag; [ "$flag" ]; }; do
if [ "$flag" != bios_grub ]; then
flags="${flags:+$flags$NL}$flag"
else
has_biosgrub=yes
fi
done
close_dialog
if [ "$method" = biosgrub ] && [ "$has_biosgrub" = no ]; then
open_dialog SET_FLAGS "$id"
write_line "$flags"
write_line bios_grub
write_line NO_MORE
close_dialog
elif [ "$method" != biosgrub ] && [ "$has_biosgrub" = yes ]; then
open_dialog SET_FLAGS "$id"
write_line "$flags"
write_line NO_MORE
close_dialog
fi
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