In Mac OS X, I could use the Activity Monitor program to see if a running program/process is 64-bit. How do I do that in a Linux OS, regardless of flavour? 
How to tell if a running program is 64-bit in Linux?
process;64bit
You can use the file command to check out what format the executable file has.eg:$ file /bin/bash/bin/bash: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.9, stripped