How can I get log messages from the LAMP server on Ubuntu 10.04?

Using cat is not a good idea, especially if logs grow large. Instead, try tailing.

sudo tail /var/log/apache2/error.log

tail will only show the last N lines of a file. If you want to keep monitoring the last lines, use the -F command-line option . Use Ctrl + C to close the monitoring.

sudo tail -F /var/log/apache2/error.log

To enable the logging, you must do that in the php.ini (look for error-logging). AFAIK that is no longer on by default in Ubuntu 10.04.

If you have to watch multiple files I'd suggest multitail. It lets you divide the screen and watch multiple files: