How can I know my Linux is running 32-bit or 64-bit?

[Stan Huang]

As title. Is there any command to know it? Can uname satisfy this question?

[Ken S]

My computer is running 64 bit Ubuntu. Here is the result of executing uname:
ken@COMPAQ-CQ57:~$ uname -p
x86_64
ken@COMPAQ-CQ57:~$

Notice x86_64. I'm not certain, but I think a 32bit machine will display i386. uname -p shows processor type. Any terminal you can open should be able to execute uname. The command arch will achieve the same.
Executing man uname will display all the options, spacebar will move on a page.