Lollapalooza weekend got off to a rough start in Chicago due to weather issues on opening night, but helping to even things out on the music scale Friday night was a Lollapalooza after show in the Windy City featuring Foo Fighters. The band wasn't on the official Lollapalooza bill, but their performance was sanctioned as an official after show and even featured a guest turn by Lolla's founder, Perry Farrell.

The Jane's Addiction vocalist popped up during the latter portion of the band's epic set at the iconic Metro club in Chicago, teasingly telling Dave Grohl there was something going on in Grant Park he should check out. Eventually Grohl coaxed Farrell to perform, as the band backed the singer on a performance of the Jane's Addiction classic "Mountain Song," which can be seen in the fan-shot video above.

"Mountain Song" was one of several covers the band pulled out during the night. Performances of the Rolling Stones' "Miss You," Queen and David Bowie's "Under Pressure," The Faces' "Stay With Me," Tom Petty and the Heartbreakers' "Breakdown" and AC/DC's "Let There Be Rock" also helped populate the early morning hours before the band eventually finished out their evening with frequent show closer "Everlong."

At the top of the show, Grohl told the audience they planned to try to break their record for their longest show ever, revealing that they were given a 4AM curfew to finish out the night. In total, the band played 32 songs during the three-and-a-half hour set, including "Run," "The Sky Is a Neighborhood," "La Dee Da" and "Sunday Rain," all from the band's upcoming Concrete and Gold disc. That album is due Sept. 15.

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