A VNC server is already running, but no lock file for that

Although there is no X11 lock on display 12, vncserver can not start that display number due to a "VNC server that is running on 12". # rm /tmp/.X12-lock rm: cannot remove ‘/tmp/.X12-lock’: No such file or directory # rm /tmp/.X11-unix/X12 rm: cannot remove ‘/tmp/.X11-unix/X12’: No such file or directory # ps aux | grep Xvnc | grep :12 # # su - metal3 -c "vncserver -geometry 1300x900 :12" A VNC server is already running as :12 New 'hpc.test.com:10 (metal3)' desktop is hpc.test.com:10 Starting applications specified in /home/metal3/.vnc/xstartup Log file is /home/metal3/.vnc/hpc.test.com:10.log Any more lock file that I have missed for killing?