/usr/share/ltsp/ltsp-server-vendor-functions is in ltsp-server 5.3.7-0ubuntu2.
This file is owned by root:root, with mode 0o644.
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 | # Debian-specific function overrides for the common functions
detect_arch() {
    if [ -x /usr/bin/dpkg ]; then
        echo $(dpkg --print-architecture)
    else
        echo "i386"
    fi
}
umount_marked() {
    [ -z "$MARKED_MOUNTS" ] && return
    echo "$MARKED_MOUNTS" | while read dir; do
        # binfmt_misc might need to be unmounted manually, see LP #534211
        if [ "$dir%/proc}" != "$dir" ] && 
            [ -d "$dir/sys/fs/binfmt_misc" ] && [ -f "$dir/mounts" ] &&
            grep -q "^binfmt_misc $dir/sys/fs/binfmt_misc" "$dir/mounts"; then
            if ! umount "$dir/sys/fs/binfmt_misc"; then
                echo "Couldn't unmount $dir/sys/fs/binfmt_misc." >&2
            fi
        fi
        if ! umount "$dir"; then
            echo "Couldn't unmount $dir." >&2
        fi
    done
}
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