VMManager not staring |Job for ovmm.service failed because the control process exited with error code. See "systemctl status ovmm.service" and "journal ctl -xe" for details.

 If Oracle VMManager not start due to disk full

# /sbin/service ovmm start

Starting ovmm (via systemctl): Job for ovmm.service failed because the control process exited with error code. See "systemctl status ovmm.service" and "journal ctl -xe" for details.

Solution

Try 

1. Check to see if ovmm_mysql service is running on Manager server:

# service ovmm_mysql status

2. If found not to be running correctly, stop it and the ovmm services:

# service ovmm_mysql stop

# service ovmm stop

3. Start ovmm_mysql:

# service ovmm_mysql start

4. Once this completes, start ovmm service:

# service ovmm start

If not working 

Check disk 

df -h

If it showing root location is full like below ,

/dev/mapper/ol_<your hostname>-root 40G 40G 20K 100% /

du -h -s /*

du -h -s /var/*

du -h -s /u01/app/oracle/ovm-manager-3/domains/ovm_domain/servers/AdminServer/logs

du -h -s /var/cache/*

du -h -s /u01/app/oracle/ovm-manager-3/domains/ovm_domain/servers/AdminServer/logs/*

Then 

1. clean up yum:

# yum clean all

# df /

2. mov /u01/app/oracle/ovm-manager-3/domains/ovm_domain/servers/AdminServer/logs/AdminServer.out to a backup location or delete it.

Then restart the ovmm service

# service ovmm_mysql start

# service ovmm start

Done :)