First show system events. Second command show events inherent to the process of booting kernel.
tail /var/log/messages tail /var/log/dmesg
View first two lines of a file
head -2 file tail -2 file # for last 2 lines
View in real time what is added to a file. -f stands for Follow
tail -f /var/log/messages
This command will let you watch a log file for changes as soon as they happen.
tail -f log/development.log