Comment 48 for bug 1205384

echo $PATH
/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games

so /usr/local/bin is before /usr/bin in my user's path.

But what about root's path? Maybe /usr/bin/lxlock will be used that way?
-----
 /usr/bin/lxlock:
...
# Try to lock the screen with thos applications (in this order) :
# lighdtm, xscreensaver, gnome-screensaver, slock, slock, i3lock and xdg-screensaver

if test x"`which dm-tool 2>/dev/null`" != x""; then
    dm-tool switch-to-greeter
elif `dbus-send --system --print-reply --dest=org.freedesktop.DBus /org/freedesktop/DBus org.freedesktop.DBus.GetNameOwner string:org.freedesktop.DisplayManager > /dev/null 2>&1` ; then
    seat="$XDG_SEAT_PATH"
    dbus-send --system --print-reply --dest=org.freedesktop.DisplayManager "$seat" org.freedesktop.DisplayManager.Seat.SwitchToGreeter \
              2> /dev/null
elif test x"`which xscreensaver-command 2>/dev/null`" != x""; then
    xscreensaver-command -lock
elif test x"`which gnome-screensaver-command 2>/dev/null`" != x""; then
    gnome-screensaver-command --lock
elif test x"`which slock 2>/dev/null`" != x""; then
    slock
elif test x"`which xlock 2>/dev/null`" != x""; then
    xlock $*
elif test x"`which i3lock 2>/dev/null`" != x""; then
    i3lock -d
# In the end, try to fallback to xdg-screensaver. Don't do at the first try,
# because if lxlock is called by xdg-screensaver, we may enter a loop.
else
    xdg-screensaver lock
fi
exit 0