The key to solving Linux related server problems is to know where the log files are stored and to be able to get to them as quickly as possible. Linux log file storage is configurable but there are some fairly standard locations on most servers where one can find the logs.. Some of the most often one used are:
Operating system log file:
/var/log/messages
Email (mail*, e.g. mail, or maillog, etc):
/var/log/mail
Security log:
/var/log/security
Generally speaking the parent directory /var/log is your best bet when looking for a log file so go and look there first.
To see what happening with a log file in real time do:
tail -f /var/log/message
In the above example the -f switch means “follow” the log, thus show in real time what is happening.
For more hints on possible locations see this Webmin article:
https://doxfer.webmin.com/Webmin/System_Logs