install and configure
On Ubuntu, you'll need to install the minicom package:
$ sudo apt-get install minicom
By default, minicom will try to do all sorts of stuff for supporting modems. This wastes time and will send various characters down to the connected system's shell, so I recommend disabling all of it. You can do that via the menus but you can also write the following to ~/.minirc.dfl once before starting minicom:
# Machine-generated file - use setup menu in minicom to change parameters.
pu port /dev/ttyS0
pu rtscts No
Note that I typically use /dev/ttyS0 (the first serial port) and you may wish to change that. If you prefer to run minicom's setup manually, try:
$ sudo minicom -s
...and then save the configuration by selecting "Save setup as dfl" from the menu.
I like to have a little launcher icon for minicom which starts the terminal with certain settings. To make one, right-click on a Gnome panel, select "Add to panel..." and then create an "Application launcher". The command that I recommend for the launcher is:
gnome-terminal --title="minicom" -e "minicom -o -w -c on"
That starts minicom in a new gnome-terminal window (titled "minicom"), with additional modem stuff disabled (-o), line wrapping enabled (-w), and color output enabled (-c on). Alternately you can just run:
minicom -o -w -c on
from your shell. minicom accepts commands after you type control+a. Its menu-driven configuration interface is activated by pressing control+a and then "o". For example, to set the baud rate, press control+a and then "o" and navigate to "Serial port setup". To exit minicom, type control+a and then "x". Keep in mind that most Linux systems use 115200 8N1 (115200 baud, 8-bit, no parity) for their serial terminal. Note that, after typing control+a, you will see a red bar on the bottom of the minicom screen with information about the current serial port configuration.
useful features / issues
You can clear the minicom screen at any time by typing control+c. minicom has a handy logging feature that enables you to capture shell output to a file. To activate it, type control+a "l" (lower-case "L") and then enter the name of the destination file (log). After that, type control+a and then "l" again to start or pause logging.
minicom is not particularly graceful with multiple instances of the application. You can use "lsof" to see if someone has the serial port open, for example:
$ lsof /dev/ttyS0
...and stop or kill the offending processes if needed. Also keep in mind that, if you use a USB serial port dongle, the kernel may assign a new device between plugging/unplugging the dongle. Be sure to tell minicom about that (ex: /dev/ttyUSB1 vs. /dev/ttyUSB0). I prefer to use the physical RS232 port on my ThinkPad's docking station rather than dealing with USB dongles.