原因：由于服务器异常重启，导致confluence无法启动服务，使用脚本startup.sh出现如下错误：

[root@swufe-application atlassian-confluence-6.15.9]# ./bin/startup.sh
If you encounter issues starting up Confluence, please see the Installation guide at http://confluence.atlassian.com/display/DOC/Confluence+Installation+Guide

Server startup logs are located in /srv/confluence/atlassian-confluence-6.15.9/logs/catalina.out
---------------------------------------------------------------------------
Using Java: /usr/local/bin/java/bin/java
2021-11-04 11:33:07,615 INFO [main] [atlassian.confluence.bootstrap.SynchronyProxyWatchdog] A Context element for ${confluence.context.path}/synchrony-proxy is found in /srv/confluence/atlassian-confluence-6.15.9/conf/s
erver.xml. No further action is required
---------------------------------------------------------------------------
Using CATALINA_BASE:   /srv/confluence/atlassian-confluence-6.15.9
Using CATALINA_HOME:   /srv/confluence/atlassian-confluence-6.15.9
Using CATALINA_TMPDIR: /srv/confluence/atlassian-confluence-6.15.9/temp
Using JRE_HOME:        /usr/local/bin/java
Using CLASSPATH:       /srv/confluence/atlassian-confluence-6.15.9/bin/bootstrap.jar:/srv/confluence/atlassian-confluence-6.15.9/bin/tomcat-juli.jar
Using CATALINA_PID:    /srv/confluence/atlassian-confluence-6.15.9/work/catalina.pid
Existing PID file found during start.
Tomcat appears to still be running with PID 11417. Start aborted.
If the following process is not a Tomcat process, remove the PID file and try again:
UID         PID   PPID  C STIME TTY          TIME CMD

其中有一句关键的话Tomcat appears to still be running with PID 11417. Start aborted.，意思是tomcat PID已经存在。但是你会发现无法查到11417的进程。

其实原因是因为服务器异常重启后，导致tomcat异常关闭，没有删除PID文件，所以在启动的时候会一直提示该PID已经存在，只需要将该PID文件删除即可，命令如下：

rm -f /srv/confluence/atlassian-confluence-6.15.9/work/catalina.pid