Artists put the finishing touches on the Perry's Stage sign at Lollapalooza in Chicago's Grant Park (Photo by Steve C. Mitchell/Invision/AP).

Music fans enter the Lollapalooza music festival in Chicago's Grant Park (Photo by Steve Mitchell/Invision/AP).

Ozzy Osbourne of Black Sabbath performs aLollapalooza on opening day in Chicago's Grant Park (Photo by Steve C. Mitchell/Invision/AP).

Dan Auerbach from The Black Keys performs at Lollapalooza in Chicago's Grant Park (Photo by Sitthixay Ditthavong/Invision/AP).

Dan Auerbach from The Black Keys performs at Lollapalooza in Chicago's Grant Park (Photo by Sitthixay Ditthavong/Invision/AP).

Fans dance their way between stages at Lollapalooza in Chicago's Grant Park (Photo by Sitthixay Ditthavong/Invision/AP).

Yolandi Vi$$er from Die Antwoord performs at Lollapalooza in Chicago's Grant Park (Photo by Sitthixay Ditthavong/Invision/AP).

Yolandi Vi$$er from Die Antwoord performs at Lollapalooza in Chicago's Grant Park (Photo by Sitthixay Ditthavong/Invision/AP).

Members of the crowd dance at Lollapalooza in Chicago's Grant Park (Photo by Sitthixay Ditthavong/Invision/AP)

James Mercer from The Shins performs at Lollapalooza in Chicago's Grant Park (Photo by Sitthixay Ditthavong/Invision/AP)

James Mercer from The Shins performs at Lollapalooza in Chicago's Grant Park (Photo by Sitthixay Ditthavong/Invision/AP)

Jessica Dobson from The Shins performs at Lollapalooza in Chicago's Grant Park (Photo by Sitthixay Ditthavong/Invision/AP)

Alex Schaaf from Yellow Ostrich performs at Lollapalooza in Chicago's Grant Park (Photo by Sitthixay Ditthavong/Invision/AP)

Fans watch a performance by Yellow Ostrich at Lollapalooza in Chicago's Grant Park (Photo by Sitthixay Ditthavong/Invision/AP)