VNC server won't start on my CentOS 7

I had to ask my boss to power down and power up the desktop in my office this morning. After the desktop came back, I could not access the vncserver because it failed to start. And I got this error when I run systemctl.

$ sudo systemctl start vncserver@\:2

Job for vncserver@:2.service failed because a configured resource limit was exceeded. See "systemctl status vncserver@:2.service" and "journalctl -xe" for details.

And I also found a Xvnc process started on :1 every time when I start the service.

I did find that `/usr/lib/systemd/system/vncserver@:2.service was missing and restored it like below:

[Unit]
Description=Remote desktop service (VNC)
After=syslog.target network.target

[Service]
Type=forking
User=bwang

# Clean any existing files in /tmp/.X11-unix environment
ExecStartPre=-/usr/bin/vncserver -kill %i
ExecStart=/usr/bin/vncserver %i -nolisten tcp -localhost -geometry 1920x1080 -de
pth 24 
PIDFile=/home/bwang/.vnc/%H%i.pid
ExecStop=-/usr/bin/vncserver -kill %i

[Install]

WantedBy=multi-user.target

And I ran systemctl daemon-reload, systemctl disable vncserver@\:2.service, systemctl enable vncserver@\:2.service multiple times, but got the same error again and again.

I also tried using vncserver\@\:2 or vncserver@:2 for service name, it won’t fix it.

Finally when I ran vncserver from the command line, it showed this message

$ vncserver :2 -nolisten tcp -localhost -geometry 1920x1080 -depth 24

Warning: bwang.corp.rhapsody.com:2 is taken because of /tmp/.X11-unix/X2
Remove this file if there is no X server bwang.corp.rhapsody.com:2
A VNC server is already running as :2

New 'bwang.corp.rhapsody.com:1 (bwang)' desktop is bwang.corp.rhapsody.com:1

Starting applications specified in /home/bwang/.vnc/xstartup
Log file is /home/bwang/.vnc/bwang.corp.rhapsody.com:1.log

Obviously, when the deskotp was powered down, /tmp/.X11-unix/X2 was left on the hard drive, and it blocked vncserver from starting on display 2 again.

Removing /tmp/.X11-unix/X2 fix the problem.

NOTE: using vncserver@:2 without escaping : is ok when running systemctl.

​