When I open one project ,apache shows the 500 page. But other links work fine.
After check the logs , I found nothing useful.
What I ’ve done these days:
(1)create a new vhost in Apache,serving a PHP site
(2)update my ubuntu 14.04,installed some updates

the version of openproject is 5.0.10

sorry for this question.The reason is this one :
(2)update my ubuntu 14.04,installed some updates

I didn’t restart ubuntu and after the update, ruby has gone.
everyting is ok after restart ubuntu.