New session rejected because of 50 session limit

SELECT SET_CONFIG_PARAMETER ('MaxClientSessions', 100);

More info can be found in the Admin Guide under the "General Parameters" 
and "Managing Sessions" pages.

Hi

We are NOT able to connect to Vertica for running below command. we are getting vsql: FATAL 4060: New session rejected due to limit, already 155 sessions active error when we try to connect to Vertica from AWS EC2 session manager.

SELECT SET_CONFIG_PARAMETER ('MaxClientSessions', 1000);

Please let me know what should be done in this case.

I also got location of the file where these session values are being stored

/proc/sys/fs/file-nr

This file is related to file-max and holds three values:

• Number of allocated file handles
• Number of used file handles
• Maximum number of file handles

Let me know whether it can be manually changed ?

You should be able to connect as dbadmin (administrator user), which can connect even when session limit is reached. If this is not the case, you may need to log onto a node and connect using vsql from a cluster node in order to raise the session limit with SET_CONFIG_PARAMETER.
The other setting for file handles in /proc can be set with ulimit as shown in the documentation, where we recommend increasing the user and system max file limits: https://docs.vertica.com/12.0.x/en/setup/set-up-on-premises/before-you-install/automatically-configured-os-settings/system-max-open-files-limit/