Sonarqube upgrade from version 5.6.6 to 6.7.5 failed

While upgrading sonarqube from version 5.6.6 to 6.7.5, I am getting the below error:

sonar web.log:

2018.11.20 11:12:10 WARN web[o.s.p.ProcessEntryPoint] Fail to start web
java.lang.IllegalArgumentException: Unable to create shared memory :
at org.sonar.process.sharedmemoryfile.AllProcessesCommands.(AllProcessesCommands.java:100)
at org.sonar.process.sharedmemoryfile.DefaultProcessCommands.(DefaultProcessCommands.java:34)
at org.sonar.process.sharedmemoryfile.DefaultProcessCommands.secondary(DefaultProcessCommands.java:52)
at org.sonar.server.app.WebServer.isOperational(WebServer.java:68)
at org.sonar.server.app.WebServer.getStatus(WebServer.java:60)
at org.sonar.process.ProcessEntryPoint.waitForOperational(ProcessEntryPoint.java:145)
at org.sonar.process.ProcessEntryPoint.launch(ProcessEntryPoint.java:120)
at org.sonar.process.ProcessEntryPoint.launch(ProcessEntryPoint.java:100)
at org.sonar.server.app.WebServer.main(WebServer.java:91)
Caused by: java.io.FileNotFoundException: /opt/sonarqube-6.7.5/temp/sharedmemory (Too many open files in system)
at java.io.RandomAccessFile.open0(Native Method)
at java.io.RandomAccessFile.open(RandomAccessFile.java:316)
at java.io.RandomAccessFile.(RandomAccessFile.java:243)
at org.sonar.process.sharedmemoryfile.AllProcessesCommands.(AllProcessesCommands.java:97)
… 8 common frames omitted

I have configured all the Unix parameter as mentioned in the upgrade document, but don’t know what’s causing the issue. Also, I am running sonar application for the sonarqube user, not the root user.

OS: RHEL 6.9

$ sysctl vm.max_map_count
vm.max_map_count = 262144

$ sysctl fs.file-max
fs.file-max = 65536

$ ulimit -n
65536

$ ulimit -u
2048

grep SECCOMP /boot/config-(uname -r)
CONFIG_SECCOMP is not set

Could you please check and let me know, how to resolve the this issue and upgrade the sonarqube.