I justed updated to the newest version of Dokuwiki. It worked for a day, and then when try to login I get a 500 error. My apache log shows:
[Fri Feb 24 16:15:59.980384 2017] [:error] [pid 1169] [client 192.168.1.28:55317] PHP Fatal error: Call to undefined function random_bytes() in /var/www/html/dokuwiki/inc/auth.php on line 333, referer:
http://IP/dokuwiki/doku.php
running PHP v7.0.3
Ubuntu 14.04.5