When to Perform Keriah if the Death Occurs During Chol Hamoed

A person whose one of the seven close relatives passed away during Chol Hamoed, should they perform keriah at the burial during Chol Hamoed, or wait until after the festival when they sit shiva?

This ruling depends on custom. The custom of Ashkenazim (and also Sephardim in Israel) is to perform keriah only for one's father and mother during Chol Hamoed, and not for other relatives. In places where there is no established custom, all relatives are required to perform keriah during Chol Hamoed. (They are permitted to change into simple clothing before performing keriah.)

Gemara Moed Katan, page 24b: "One does not tear, nor remove shoes, nor provide a meal, except for the relatives of the deceased." This is also stated in Shulchan Aruch, Yoreh De'ah, Siman 340, Paragraph 31, and in Orach Chaim, Siman 547, Paragraph 7, as the ruling of the Gemara to tear for all obligatory keriah during Chol Hamoed (and what is written "except for the relatives of the deceased" excludes tearing due to sorrow, and Beit Yosef brings that there are those who disagree and hold that the Mishnah excludes one standing at the time of the soul's departure and a righteous person who is not a relative). The Rema brings the custom of the Maharil (Laws of Chol Hamoed, page 198, Siman 16) that one does not tear during the festival except for one's father and mother. This is the custom in Ashkenaz, and Mishnah Berurah writes that in Poland this was not the custom, and they would tear for all relatives. The Rema writes that in places where there is no custom, one tears for all.