Log file is a file which stores all the information of all files that are accessed, and they also have errors which help a system administrator to troubleshoot issues and fixing them to make the web server stable. Few logs can be found below:

Apache web server

path:/usr/local/apache/logs/access_log
path: /usr/local/apache/logs/error_log
path: /usr/local/apache/domlogs/domain.com

MySQL database server

/path:var/lib/mysql/server.hostname.com.err

Exim mail server

/path:var/log/exim_mainlog
path: /var/log/exim_paniclog
path: /var/log/exim_rejectlog

Courier-IMAP

/path:var/log/maillog

cPanel control panel

/path:usr/local/cpanel/logs/error_log
path: /usr/local/cpanel/logs/access_log
path: /usr/local/cpanel/logs/license_log
path: /usr/local/cpanel/logs/login_log
path: /usr/local/cpanel/logs/stats_log

FTP server

/path:var/log/messages
path: /var/log/xferlog

System logs

/path:var/log/messages
path: /var/log/boot.log
path: /var/log/cron
path: /var/log/dmesg

Security logs

path:/var/log/secure
path: /var/log/messages