正如here和here所述，我正在尝试（在Ubuntu 16.04上）在端口80上启动Tomcat 9.0.2，让systemd预先初始化套接字特权端口，然后将其传递给作为非特权用户“tomcat”运行的Tomcat（我知道还有其他解决方案，但我有兴趣使这个工作）。为此，我有以下套接字单元（“port”设置已在server.xml上更改为80）：
/etc/sytemd/system/tomcat.socket
[Unit]
Description=Tomcat server socket
[Socket]
ListenStream=80
以下服务单位：
/etc/sytemd/system/tomcat.service
[Unit]
Description=Apache Tomcat Web Application Container
After=syslog.target network.target
[Service]
Type=forking
Environment=CATALINA_PID=/opt/tomcat/9.0.2/temp/tomcat.pid
Environment=CATALINA_HOME=/opt/tomcat/9.0.2
ExecStart=/opt/tomcat/9.0.2/bin/startup.sh
ExecStop=/opt/tomcat/9.0.2/bin/shutdown.sh
User=tomcat
Group=tomcat
UMask=0007
[Install]
Requires=tomcat.socket
运行sudo systemctl start tomcat.service时，该命令不会输出任何错误消息，但systemctl status tomcat.service显示失败状态：
tomcat.service - Apache Tomcat Web Application Container
Loaded: loaded (/etc/systemd/system/tomcat.service; static; vendor preset: enabled)
Active: failed (Result: exit-code) since Tue 2017-12-19 21:46:53 -05; 45min ago
Process: 10207 ExecStop=/opt/tomcat/9.0.2/bin/shutdown.sh (code=exited, status=1/FAILURE)
Process: 10175 ExecStart=/opt/tomcat/9.0.2/bin/startup.sh (code=exited, status=0/SUCCESS)
Main PID: 10189 (code=exited, status=0/SUCCESS)
从下面的journald日志中可以看出，Tomcat确实已启动，但shutdown.sh会立即运行并退出。显然，Tomcat仍尝试在端口80上创建一个套接字，该套接字失败，因为用户tomcat不是超级用户，并立即退出。
systemd[1]: Starting Apache Tomcat Web Application Container...
startup.sh[10175]: Existing PID file found during start.
startup.sh[10175]: Removing/clearing stale PID file.
startup.sh[10175]: Tomcat started.
systemd[1]: Started Apache Tomcat Web Application Container.
sudo[10172]: pam_unix(sudo:session): session closed for user root
shutdown.sh[10207]: PID file found but no matching process was found. Stop aborted.
systemd[1]: tomcat.service: Control process exited, code=exited status=1
systemd[1]: tomcat.service: Unit entered failed state.
systemd[1]: tomcat.service: Failed with result 'exit-code'.
如果Tomcat 9能够从systemd接收预初始化的套接字，我该如何使其工作？或者Tomcat无法这样做？