Can one use the same Shamash to light other Menorahs or does one have to have his own Shamash?

There is no obligation to use a Shamash altogether, however the custom is to use it for the following purposes: 1. In order to light the Chanukah candles. 2. We place the Shamash that was used for lighting or a different additional candle near the Menorah in order not to use the light of the Chanukah candles. Therefore it is permitted to use one Shamash to light as many Menorahs as you wish. As far as the candle that is placed near the Menorah, it depends; if the Menorahs are far apart, as is proper, then one should place a special Shamash by each Menorah so he should not use its light, but if the Menorahs are concentrated in one area then one Shamash suffices for all the Menorahs. [שו"ע ורמ"א סימן תרעג ומ"ב ס"ק יד-כ].