/usr/lib/ubiquity/compat/linux-boot-prober is in ubiquity 2.18.7.
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 | #! /bin/sh
# A caching version of linux-boot-prober.
set -e
dev="$(echo "$1" | sed 's,/,=,g')"
cache="/var/lib/ubiquity/linux-boot-prober-cache/$dev"
if [ ! -e "$cache" ]; then
mkdir -p "${cache%/*}"
PATH=/usr/sbin:/sbin:/usr/bin:/bin linux-boot-prober "$1" >"$cache"
fi
cat "$cache"
exit 0
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