Current reputation systems for peer-to-peer (P2P) file sharing systems either fail to utilize existing trust within social networks or suffer from certain attacks (e.g., free-riding and collusion). To handle these problems, we introduce a trust management system, called SocialLink, that utilizes social network and historical transaction links. SocialLink manages file transactions through both the social network and a novel weighted transaction network, which is built based on previous file transaction history. First, SocialLink exploits the trust among friends in social networks by enabling two friends to share files directly. Second, the weighted transaction network is utilized to 1) deduce the trust of the client on a server in reliably providing the requested file and 2) check the fairness of the transaction. In this way, SocialLink prevents potential misbehaving transactions (i.e., providing faulty files), encourages nodes to contribute file resources to non-friends, and avoids free-riding. Furthermore, the weighted transaction network helps SocialLink resist whitewashing, collusion and Sybil attacks. Extensive simulation demonstrates that SocialLink can efficiently ensure trustable and fair P2P file sharing and resist the aforementioned attacks.