It very important to have clear understanding and reference to location of your cPanel VPS log files. This is the case in case of web attacks , security relayed issues or just good old troubleshooting. This is very basic overview of all log files used by cPanel and where they are locate.
Exim is the MTA(Mail Transfer Agent) that cPanel utilizes.
The exim_mainlog contains ALL interactions that exim handles, so both incoming and outgoing mail transactions.
The exim_rejectlog contains all connection attempts that were denied. This information is also logged in the exim_mainlog.
Cpanel http traffic to WHM, webmail, and cPanel access.
All cPanel logs are located in the /usr/local/cpanel/logs directory.
This access_log contains all traffic to WHM, cPanel, and webmail over http.
This error_log contains all errors that occur when accessing a cPanel related site over http or https.
Each site has its own traffic log.
The access_log is used to log all http requests to ether the hostname of the server, requests directed at the servers IPs, or sites that resolve to the server but are no longer hosted on it.
On cPanel servers all Apache errors, regardless of site, are logged in the error_log.
Within the domlogs folder each site on the server will have its own log file. These files will be the fully qualified domain name for the domain, ie domain.com, liquidweb.com. All http traffic to a site will be logged in this log file.
All ftp log files located here.