I came across a problem recently, I needed to configure a Cisco switch and all I had was a Ubuntu machine that had a serial port. Since then I've got a Cisco 2511, with octal cable, which is very handy when configuring many devices, but that is for another post.
I found a program called 'minicom' which is available as far as I'm aware in all the main repositories. This post is a brief explanation on how to find your serial port and setup / use minicom.
1. First of all lets start with finding the computers serial ports, make sure you have your device powered on and connected:
dmesg | grep tty
This shows in my example that the physical serial port is at ttyS0, where as usb > serial converters will show as ttyUSB0
2. Time to open up minicom, I believe the later versions will allow running as an unprivileged user, but this will mean that you can not save configurations. Better to run as root if you have the option.
3. Checking the options available is very easy, to put minicom in to command mode control+a needs to be pressed, with a following 'z' to show the options. For example, control+a then x will close minicom.
4. Now it is time to setup minicom, as you can see from the help page you need to use control+a then o (for options). Scroll down to "Serial port setup" and hit enter.
5. From there is is pretty straight forward to follow the prompts to change to your required settings. Typically Cisco networking equipment uses 9600 Bps/Par/Bits, "8-N-1", Yes to Hardware Control Flow and no to Software Control Flow. Also set your serial device to the one you found in the first step.
6. Now save your configuration for quicker access in the future, personally I save it as "Cisco".
7. Now close minicom with control+a then x will prompt you the option to close the program or simply scroll to "Exit".
8. If you saved a configuration within minicom, it can be used to open minicom directly in to those settings. For example, "minicom cisco".
9. Everything should be ready for using your serial device.