"Too many open files" but what are they?

java.io.FileNotFoundException: /opt/tb55/s3/conf/web.xml (Too many open files) at java.io.FileInputStream.open(Native Method) at java.io.FileInputStream.<init>(FileInputStream.java:106)

this shows the open file limit has been reached.. you can check this by JMX

java.lang:type=OperatingSystem >  OpenFileDescriptorCount

but what are these files ? you can see this by linux shell script

lsof -u tomcat

solution: increase systems open file limit !!!

vi /etc/security/limits.conf

and edit the line to increase open file limit

* soft nofile 3072
* hard nofile 4048