Familiar rituals of grief marked the seventh anniversary of Sept. 11 on Thursday as thousands paid tribute at the attack sites, the presidential candidates laid flowers at ground zero and children mourned parents they can barely remember.Sens. John McCain and Barack Obama called off their campaigns for the day, and in the late afternoon descended the long ramp into the pit of the World Trade Center site, bowing their heads and leaving the flowers in a reflecting pool.At the Pentagon, 15,000 people turned out for the dedication of the first permanent memorial built at any of the three sites where hijacked planes crashed. It includes 184 benches that will glow at night, one for each victim there."Thanks to the brave men and women, and all those who work to keep us safe, there has not been another attack on our soil in 2,557 days," President Bush said at the outdoor dedication.In New York, the crowd fell silent in a park just east of the trade center site at 8:46, 9:03, 9:59 and 10:29 a.m. — the times when two hijacked jets slammed into the buildings and the twin towers fell.Family members of the trade center dead and students representing the more than 90 countries that lost citizens in the attack — Azerbaijan to Zambia to Vietnam — read the names of the 2,751 victims killed in New York.Others descended seven stories below street level to pay respects where the towers once stood. A giant crane, an American flag hanging from a hook, overlooked the anniversary ceremony from ground zero, where office towers, a memorial and transit hub are under construction.The New York memorial is years away from completion. Some of the mourners worried the progress on it would prevent them from being allowed to pay respects next Sept. 11 on the ground where their loved ones died.Obama, in a statement, recalled that after the attacks, "Americans across our great country came together to stand with the families of the victims, to donate blood, to give to charity, and to say a prayer for our country. Let us renew that."In New York, relatives of victims began arriving at dawn for the memorials, wearing their loved ones' pictures on T-shirts and holding signs saying, "We miss you,""We love you" or "You will never be forgotten."info: SFGate