How to view system log messages in unix?

Q. where are the log files are  located under redhat or  Debian or Cento OS Linux server? How do I open or view log files? 

 Almost all log files are located under /var/log directory (and subdirectory). You can change to this directory using cd command. You can use less, more, cat or tail command to see the logs.  To Go to /var/logs directory:

# cd  /var/log/

# ls

To View common log file /var/log/messages using any one of the following command: 


# tail -f /var/log/messages, used in real time, it will show last 10 logs

# less /var/log/messages

# more /var/log/messages, we can see page page, press Tab to toggle between pages.

# vi /var/log/messages , to see in vi editor


# cat /var/log/messages


 Q. what is the use of log messages?

• logs are used to see the status of your system. which provides the error messages and services return messages
• with the help of logs we can trouble shoot the system erors

Linux Log files and usage

/var/log/dmesg  --> used for kernel boot messages

/var/log/messages  --> stores the standard system error messages

/var/log/maillog  --> mail system messages


/var/log/secure -->  security , authentication messages

/var/log/audit/audit.log -->  kernel auditing messages

var/log/debug -->Debugging log messages

 /var/log/faillog --> User failed login log file

/var/log/kern.log --> Kernel log file

 /var/log/lpr.log -->Printer log file

 /var/log/mail.* : All mail server message log files

 /var/log/mysql.* : MySQL server log file

 /var/log/user.log : All userlevel logs

 /var/log/xorg.0.log : X.org log file

/var/log/apache2/* : Apache web server log files directory

 /var/log/lighttpd/* : Lighttpd web server log files directory

/var/log/fsck/* : fsck command log

/var/log/apport.log : Application crash report