OpenNebula

systemctl start opennebula-novnc.service
Job for opennebula-novnc.service failed because the control process exited with error code. See "systemctl status opennebula-novnc.service" and "journalctl -xe" for details.

this is because of the following:

E, [2016-06-29T11:47:00.296084 #820] ERROR -- : No such file or directory @ rb_sysopen - /var/lock/one/.novnc.lock

In the opennebula-novnc.service there is a reference to a PIDFile:

PIDFile=/var/lock/one/.novnc.lock

but the directory /var/lock/one does not exist, and hence the process can not be started. Manually creating the directory, making it owner/group oneadmin and restarting opennebula-novnc.service fixes this issue (until next reboot).

Systemd manual says the following about PIDFile:

PIDFile=

Takes an absolute file name pointing to the PID file of this daemon. Use of this option is recommended for services where Type= is set to forking. systemd will read the PID of the main process of the daemon after start-up of the service. systemd will not write to the file configured here, although it will remove the file after the service has shut down if it still exists.

So it should be created before starting novnc proxy ....

This all has been tested on Ubuntu 16.04 with Sunstone running under Apache passenger