How to determine whether I run a 32bit or 64bit Ubuntu install

"Did you try uname -m ?

It seems like the uname -m actually gives

x86_64 when it is an kernel 64 bits
i686 for 32 bits kernel

Otherwise, not for the Linux kernel, but for the CPU, you type:

cat /proc/cpuinfo

or:

grep flags /proc/cpuinfo

Under ""flags"" parameter, you will see various values. Among them, one is named ""tm(transparent mode)"" or ""rm(real mode)"" or ""lm(long mode)""

rm means: 16 bit processor
tm means: 32 bit processor
lm means: 64 bit processor

Note: you can have a 64-bit CPU with a 32-bit kernel installed""

Source."