Linux log files location and how do I view logs files?

Q. I am new to Linux and I would like to know where are the log files located under Debian or Cento OS Linux server? How do I open or view log files?

A. Almost all logfiles are located under /var/log directory (and subdirectory). You can change to this directory using cd command but you need to be the root user. You can use less, more, cat or tail command to see the logs.

Go to /var/logs directory:# cd /var/logsView common log file /var/log/messages using any one of the following command:# tail -f /var/log/messages
# less /var/log/messages
# more -f /var/log/messages
# vi /var/log/messagesOutput:

Jul 17 22:04:25 router  dnsprobe[276]: dns query failed
Jul 17 22:04:29 router last message repeated 2 times
Jul 17 22:04:29 router  dnsprobe[276]: Primary DNS server Is Down... Switching To Secondary DNS server
Jul 17 22:05:08 router  dnsprobe[276]: Switching Back To Primary DNS server
Jul 17 22:26:11 debian -- MARK --
Jul 17 22:46:11 debian -- MARK --
Jul 17 22:47:36 router  -- MARK --
Jul 17 22:47:36 router  dnsprobe[276]: dns query failed
Jul 17 22:47:38  debian kernel: rtc: lost some interrupts at 1024Hz.
Jun 17 22:47:39  debian kernel: IN=eth0 OUT= MAC=00:0f:ea:91:04:07:00:08:5c:00:00:01:08:00 SRC=61.4.218.24 DST=192.168.1.100 LEN=60 TOS=0x00 PREC=0x00 TTL=46 ID=21599 DF PROTO=TCP SPT=59297 DPT=22 WINDOW=5840 RES=0x00 SYN URGP=0

Common Linux log files name and usage

• /var/log/message: General message and system related stuff
• /var/log/auth.log: Authenication logs
• /var/log/kern.log: Kernel logs
• /var/log/cron.log: Crond logs (cron job)
• /var/log/maillog: Mail server logs
• /var/log/qmail/ : Qmail log directory (more files inside this directory)
• /var/log/httpd/: Apache access and error logs directory
• /var/log/lighttpd: Lighttpd access and error logs directory
• /var/log/boot.log : System boot log
• /var/log/mysqld.log: MySQL database server log file
• /var/log/secure: Authentication log
• /var/log/utmp or /var/log/wtmp : Login records file
• /var/log/yum.log: Yum log files

In short /var/log is the location where you should find all Linux logs file. However some applications such as httpd have a directory within /var/log/ for their own log files. You can rotate log file using logrotate software and monitor logs files using logwatch software.