I'm using Plesk 12.5.30 on Ubuntu 14.04.
Trying to access Plesk panel, I get a 502 Bad Gateway since this morning.
/var/log/sw-cp-server/error_log has
/etc/init.d/psa stopall && /etc/init.d/psa startall results in
/etc/init.d/sw-engine start gives me
/var/log/sw-cp-server/sw-engine.log...