US government shutdown: What closes, what stays open?

If Congress fails to provide funding for the fiscal year starting October 1, many US government services would be disrupted and hundreds of thousands of federal workers would be furloughed without pay. Essential workers would remain on the job, but without pay. The military, law enforcement agencies, federal courts, airport security, and air-traffic control would continue to operate. However, museums, scientific research agencies, national parks, and social programs such as Head Start and nutrition benefits could be affected. The White House and the US Postal Service would be unaffected.