May one make a Matzeihvah ceremony during the 9 days e.g. this year on 2 Av?
It says in Shulchan Aruch, Orach Chaim 551,2; that from Rosh Chodesh Av until the fast one should lessen his business and any building of happiness etc. Building means a place of residential use. Setting up a gravestone is not building at all, and certainly is not happiness. Setting up a gravestone is in honor of the dead (and for other reasons see Sefer Kol-Bo on Avelut by Rabbi Yekutiel Yehuda Greenwald 5, 3a). Therefore it is clearly permitted to set up a gravestone and to practice all the related customs during the Nine Days. I found in Sefer Kitzur Hilchot Avelut from Sefer Nishmat Yisrael of Rabbi Yisrael David Harfenes (Brooklyn NY year 5764, end of chapter 35) that even on Tisha B'Av itself one is allowed to set up a gravestone [and after midday one can say the verses from Tehilim (Psalms) which are customarily said]. Regarding saying an eulogy at the setting up of a gravestone, one should not say too much words of eulogy but be focused on praises of the deceased. It is praiseworthy to talk about the destruction of the Temple, may it be built speedily in our times, Amen.