org.apache.catalina.startup.ContextConfig.beforeStart Exception fixing docBase for context [/demo]

idea在启动tomcat的时候报以下错误:

04-Mar-2020 15:56:19.381 SEVERE [RMI TCP Connection(2)-127.0.0.1] org.apache.catalina.startup.ContextConfig.beforeStart Exception fixing docBase for context [/demo]
    java.io.IOException: Unable to create the directory [/opt/tomcat8.5/webapps/demo]
        at org.apache.catalina.startup.ExpandWar.expand(ExpandWar.java:115)
        at org.apache.catalina.startup.ContextConfig.fixDocBase(ContextConfig.java:616)
        at org.apache.catalina.startup.ContextConfig.beforeStart(ContextConfig.java:749)
        at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:301)
        at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:123)
        at org.apache.catalina.util.LifecycleBase.setStateInternal(LifecycleBase.java:423)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:182)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:743)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:719)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:705)
        at org.apache.catalina.startup.HostConfig.manageApp(HostConfig.java:1720)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:287)
        at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
        at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
        at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:479)
        at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:428)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:287)
        at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
        at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
        at com.sun.jmx.remote.security.MBeanServerAccessController.invoke(MBeanServerAccessController.java:468)
        at javax.management.remote.rmi.RMIConnectionImpl.doOperation(RMIConnectionImpl.java:1468)
        at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:76)
        at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1309)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1408)
        at javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:829)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:357)
        at sun.rmi.transport.Transport$1.run(Transport.java:200)
        at sun.rmi.transport.Transport$1.run(Transport.java:197)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.Transport.serviceCall(Transport.java:196)
        at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:573)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:834)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:688)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:687)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

原因是在linux中读写tomcat文件夹需要root权限，解决方法有两种

1. 以root用户启动idea
2. 修改tomcat文件夹的权限

# 可以直接修改tomcat的文件夹
sudo chmod 777 $CATALINA_HOME
# 也可以只修改tomcat下的webapps文件夹
sudo chmod 777 $CATALINA_HOME/webapps