The command tail -f will display the last 10 lines of a file, and then continuously wait for new lines, and display them as they appear.
$ tail -f /var/log/messages
If you want to see more than ten lines at the outset, specify the new number (say 50 lines) like this:
$ tail -50 -f /var/log/messages
The tail command is fast and simple. But if you want more than just following a file (e.g., scrolling and searching), then less may be the command for you.
$ less /var/log/messages
Press Shift-F. This will take you to the end of the file, and continuously display new contents. In other words, it behaves just like tail -f.
To start less in the tail mode (thanks to Seth Milliken for this tip), execute:
$ less +F /var/log/messages
To scroll backwards, you must first exit the follow mode by pressing Control-c. Then, you can scroll back by pressing b. In fact, all the less commands are available to you once you are in the regular less mode. You can start a search by typing / followed by the string you want to search for.
Happy Log Watching !!!
Related articles on tailing files:
Tail multiple files
Two additional ways to tail a log file