NSFileManager & NSFilePosixPermissions

First, NSFilePosixPermissions is the name of a constant. Its value may also be the same, but that’s not guaranteed. The value of the NSFilePosixPermissions constant could change between framework releases, e. g. from @"NSFilePosixPermissions" to @"posixPermisions". This would break your code. The right way is to use the constant as NSFilePosixPermissions, not @"NSFilePosixPermissions".

Also, the NSFilePosixPermissions reference says about NSFilePosixPermisions:

The corresponding value is an NSNumber object. Use the shortValue method to retrieve the integer value for the permissions.

The proper way to set POSIX permissions is:

// chmod permissions 777

// Swift
attributes[NSFilePosixPermissions] = 0o777

// Objective-C
[attributes setValue:[NSNumber numberWithShort:0777] 
             forKey:NSFilePosixPermissions];

Solution in Swift 3

let fm = FileManager.default

var attributes = [FileAttributeKey : Any]()
attributes[.posixPermissions] = 0o777
do {
    try fm.setAttributes(attributes, ofItemAtPath: path.path)
}catch let error {
    print("Permissions error: ", error)
}