To troubleshoot an issue with your VPS, use the following resources.

cPanel Service Daemons

cpsrvd - cPanel Main daemon
cpanellogd - Stats processing daemon
tailwatchd - Daemon that handles eximstats - cPBandwd - chksrvd - antirelayd
cpdavd - webdav daemon
cPHulkd - pam based brute force protection (does not use iptables, blocks are user based)
mailman - qrunner
queuprocd - queue processing daemon - handles queuing of httpd and named restarts.
httpd - Apache daemon
imap - Imap daemon
pop3 - Pop3 daemon
pure-ftpd - FTP Server daemon
named - Bind DNS daemon 
 

Error Logs

cPanel

/usr/local/cpanel/logs/error_log
/usr/local/cpanel/logs/access_log
/usr/local/cpanel/logs/license_log (cPanel License update log) 

Apache

/usr/local/apache/logs/error_log (Apache Error Log)
/usr/local/cpanel/logs/easy/apache/ (easyapache update logs) 

System

/var/log/messages (FTP, Suhosin, Kernel Logs)
/var/log/boot.log
/var/log/cron 

Security

/var/log/secure (Login Log)
/usr/local/apache/logs/audit_log 

Mail

/var/log/exim_mainlog (Exim SMTP Log)
/var/log/maillog (IMAP, POP3 Log)

cPanel Update Logs

/var/cpanel/updatelogs/ (UPCP Logs) 

MySQL

/var/lib/mysql/your.hostname.com.err 

Backups

/usr/local/cpanel/logs/cpbackup