The log files plays an important role in error trouble shooting process. Different control panels have different log files and location. Here is some important and commonly using log files for linux server which has Directadmin as control panel.
Default DirectAdmin log files:
# /var/log/directadmin/error.log
# /var/log/directadmin/errortaskq.log
# /var/log/directadmin/system.log
# /var/log/directadmin/security.log
Default webserver log files (Apache);
# /var/log/httpd/error_log
# /var/log/httpd/access_log
# /var/log/httpd/suexec_log
# /var/log/httpd/fpexec_log
# /var/log/httpd/domains/domain.com.error.log
# /var/log/httpd/domains/domain.com.log
# /var/log/messages (generic errors)
FTP:
Proftpd:
#/var/log/proftpd/access.log
#/var/log/proftpd/auth.log
#/var/log/messages (generic errors)
PureFTPd:
# /var/log/pureftpd.log
Dovecot and vm-pop3d:
# /var/log/maillog
# /var/log/messages
named (bind):
# /var/log/messages
exim:
# /var/log/exim/mainlog
# /var/log/exim/paniclog
# /var/log/exim/processlog
# /var/log/exim/rejectlog
mysqld:
RedHat:
# /var/lib/mysql/server.hostname.com.err
FreeBSD and Debian:
# /usr/local/mysql/data/server.hostname.com.err
crond:
# /var/log/cron
You can use the following commands to view log files:
less /log/location   : Static view 
tail -f Or tailf /log/location  Dynamic view
That’s it :-)