WASHINGTON - US President Barack Obama was sworn in for a second term in office on Sunday in a small, private ceremony in the White House's Blue Room.Chief Justice John Roberts, who leads the US Supreme Court, administered the oath of office to the president, repeating a role he took in 2009, when Obama became the first black president of the United States.Obama's swearing-in, witnessed by family, met the constitutional requirement that he take the oath on January 20. He will repeat the procedure in a public ceremony in front of the US Capitol on Monday.