Since old Ubuntu LTS doesn’t update package anymore,
some patches need add by yourself,
like munin if_ error.

: plugins/node.d.linux/if_

    # iwlist first)
    if [[ -r /sys/class/net/$INTERFACE/speed ]]; then
            SPEED=$(cat /sys/class/net/$INTERFACE/speed 2>/dev/null)
-           if [[ "$SPEED" -gt 0 ]]; then
+           if [ -n "$SPEED" -a "$SPEED" -gt "0" ]; then
                echo $SPEED
                return
            fi