It is sufficient to greet the dead with salaam once when first entering the graveyard
Question

                Is it sufficient to greet the dead with salaam once when first entering the graveyard?
Praise be to Allah.That is sufficient, and that achieves the purpose of visiting 
          the graves. If the graves are far away and one visits them from all 
          directions, that is OK. 
 Kitaab Majmoo’ Fataawa wa Maqaalaat Mutanawwi’ah 
          li Samaahat al-Shaykh ‘Abd al-‘Azeez ibn ‘Abd-Allaah ibn Baaz (may Allaah 
          have mercy on him), vol. 13, p. 335. 
 The shaykh (may Allaah have mercy on him) was also 
          asked: 
When visiting the graves, is it prescribed for the visitor to go to 
          the particular grave that he wants to visit? 
 He (may Allaah have mercy on him) answered: 
It is sufficient for him (to say salaams) at the first graves he comes 
          to, but if he wants to go to the grave of the person that he wants to 
          visit and say salaams to him, then that is OK.