We are really sorry for continued issues with running iOS builds.
Due to a permissions change in iOS 8/Xcode 6, the iOS simulator is no longer starting when launched by a process that is run from SSHd. This issue has been reported to Apple but is unlikely to be fixed anytime soon. You can read more about it here: http://openradar.io/18321293
We are looking into a potential fix (bypassing SSH completely). If we don't get it out by today, we will roll back to Xcode 5. Unfortunately, due to our Mac infrastructure internals, we cannot have two VM images installed simultaneously, which is a separate issue we are trying to address as soon as possible.
Previously, we announced a rollback for last Friday, but did hold it back, since we had found a potential fix for the issue, only to discover it not working on the exact OS X version we have installed on our VMs.
We are also working on a full postmortem so we can share this information with all users and customers of travis-ci.org and travis-ci.com, as well as what we are doing to make sure this does not happen again.