Q. If someone always makes a seuda with meat on every Rosh Chodesh, can he also do so on Rosh Chodesh Av? Especially when it falls, as in this year on Friday and Tisha Beav is nidche?
A. Many Poskim maintain that one should abstain from eating meat on Rosh Chodesh Av (Maharil, 551, Mogen Avrohom (ibid 26), Maamar Mordechai (ibid. 9), Mishna Berura (ibid. 56) and others.
However, some permit for those who do so on every Rosh Chodesh (Chavas Daas, 26, Chida – More Baetzva 8: 233, Kaf Hachaim 26, mentions that this was the tradition of the Sefaradim in Yerushalaim.
Shulchan Aruch (O.H. 580) counts Rosh Chodesh Av as a day of fasting and Taanis Tzadikim, since it is the day of the petirah of Aharon Hacohen,
Horav Shlomo Miller’s Shlit’a opinion is that one should follow the minhag of his family or community.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a