A new OpenVZ VPS does not start: Can't open /sys/fs/cgroup/ve/101/ve.ip_allow for writing: No such file or directory

Symptoms 

• A new OpenVZ 7 VPS does not start:

  CONFIG_TEXT: Can't open /sys/fs/cgroup/ve/101/ve.ip_allow for writing: No such file or directory
  Unable to add ip 203.0.113.2: No such file or directory
  Cancel init execution

• When trying to list VPSes with prlctl utility the following error is generated:

  CONFIG_TEXT: Login failed: Unable to connect to Virtuozzo. You may experience a connection problem or the server may be down. Contact your Virtuozzo administrator for assistance.

Cause

prl-disp-* packages are missing on the node.

Resolution

1. Connect to OpenVZ node via SSH
2. Install missing packages:

   # yum install prl-disp-*

3. Enable and start prl-disp service:

   # systemctl enable prl-disp.service
   # systemctl start prl-disp.service

4. Restart vz service:

   # systemctl restart vz