Where are all the major log files located?

All log files are located in /var/log directory. In that directory, there are specific files for each type of logs. For example, system logs, such as kernel activities are logged in syslog file.

• Some of the most common log files in that directory is : 
• In directory apt there is a file history.log which saves all the package installation and removal information even the initial system build as Live CD. You can open this file to see this very interesting file. 
• In directory dist-upgrade there is a file apt.log which logs the information during distribution upgrades 
• In directory installer the log files which are created during installation can be found. 
• There is an apport.log file which saves information about crashes in your system and reporting them. 
• The file auth.log includes information about the authentication activities such as when you authenticate as root user via sudo. 
• The file dpkg.log saves the low level details of package installation and removal related with dpkg. You might be aware that, Apt system depends on dpkg for package installation and removal. 
• boot.log includes information of each booting. 
• kern.log saves kernel information such as warnings, errors etc. 
• alternatives.log includes the history of all the alternatives set by various packages and there removal via update-alternatives command. 
• Another important log file is Xorg.log which include information about the graphics driver, it's failures, warnings etc. 

Some other types of Log files may be there depending on your installed packages. For example, My system also includes a log files epoptes.log which will only be there if you install epoptes package.