Generally, 'uname -m' should report x86_64 for 64-bit (amd64) and i686
for 32-bit (x86).
... another check can be 'file /sbin/init' which will report as something along the lines of
"/sbin/init: ELF 64-bit LSB executable, x86-64, version 1 (SYSV),
dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for
GNU/Linux 2.6.32, stripped"